By the Light of the Pony

Light-emitting organs have evolved in many different species of marine fish. For the greater part, they are associated with inhabitants of the deep sea, the twilight and midnight zones beyond the reach of celestial light. Light production by species found in shallow waters is much less common. Nevertheless, one particularly notable radiation of near-surface glowers is the ponyfishes of the family Leiognathidae.

Leiognathus equulus, copyright Sahat Ratmuangkhwang.

Ponyfishes are small, mostly silvery fishes found in coastal and brackish waters in tropical regions of the Indo-West Pacific. The largest ponyfishes grow to about 25 cm in length but most species are much smaller (Woodland et al. 2002). They live in large schools that forage near the surface at night, descending close to the bottom sediment during the day. Why these animals are referred to as 'ponyfishes', I have no idea (perhaps the head is meant to look a bit pony-like?) An alternative vernacular name of 'slipmouth' makes a lot more sense as these fish have highly extensible jaws that can be used to snipe prey out of the water. A groove along the top of the skull allows for reception of a long, mobile premaxilla, supporting the mouth as an elongate tube when extended. Most ponyfishes are planktivores with simple, minute teeth in the jaw and the mouth extending horizontally. Species of the genus Deveximentum have the mouth tilted obliquely at rest so that it stretches upwards when extended. Members of the genus Gazza are piscivores when mature, feeding on other fish, and possess a pair of large caniniform teeth in each of the upper and lower jaws to hold their prey (James 1975).

Ponyishes are also notable for their elaborate light-producing organs. In most bioluminescent fishes, the photophores sit on or close to the skin surface but in leiognathids it is an internal outgrowth of the gut. A cavity around the end of the oesophagus houses colonies of bioluminescent bacteria, usually the species Photobacterium leiognathi. This light organ sits alongside or projects into the gas bladder which has a reflective internal coating. In many species, patches of scale-less, translucent skin allow the transmitted light to shine forth brightly. Muscular 'shutters' associated with the light organ allow the fish to control light transmission more directly (Woodland et al. 2002).

Photopectoralis bindus, copyright D. G. R. Wiadnya.

In a review of ponyfish taxonomy by James (1975), no mention was made of the light-emitting organ or many of its associated structures (though reference was made to the absence of scales on certain parts of the body). With the exceptions of the distinctive genera Gazza and Deveximentum, ponyfishes were assigned to a broad genus Leiognathus. Since then, variations in the structure of the light organ have been recognised as taxonomically significant, allowing the recognition of several genera divided between two subfamilies Leiognathinae and Gazzinae (Chakrabarty et al. 2011). Leiognathinae is defined by plesiomorphic characters and is likely to be paraphyletic to Gazzinae (Sparks & Chakrabarty 2015).

Because of the nocturnal habits of ponyfish and the delicacy of the light-emitting structures, our understanding of how light production functions in Leiognathidae remains somewhat limited. In Leiognathinae and females of Gazzinae, the light organ is relatively small and the external body surface lacks translucent patches. For the most part, light is expressed in these individuals as a uniform ventral glow that probably functions as counter-illumination (the light from the venter prevents the fish from appearing as a silhouette against light from the water surface to predators swimming below). Alternatively, light may be flashed to warn school-mates of danger. In males of Gazzinae, conversely, the light organ is enlarged relative to females and associated with translucent 'windows'. The shape of the organ and the arrangement of the 'windows' is a primary factor in distinguishing genera. Rhythmic flashing of light has been observed in males of many gazzine species and is probably characteristic of the group as a whole. Woodland et al. (2002) observed a school of several hundred Eubleekeria splendens flashing their lights synchronously shortly after nightfall. The exact function of such displays is uncertain, whether in courtship displays, co-ordinating school movements, attracting prey or dissuading predators. The sexually dimorphic nature of the light organ system, together with its species-specific expression, might seem to favour the first of these options but it should be noted that they are not all mutually exclusive.

Despite their small size, ponyfishes are often significant food fish for people living in areas where they are found. Thanks to their schooling behaviour, they are often a major component of dredge catches. In the Philippines, they are used for making bagoong, a fermented fish paste. In other places, they may be cooked whole after cleaning. The glow, sadly, does not survive the process.

REFERENCES

Chakrabarty, P., M. P. Davis, W. L. Smith, R. Berquist, K. M. Gledhill, L. R. Frank & J. S. Sparks. 2011. Evolution of the light organ system in ponyfishes (Teleostei: Leiognathidae). Journal of Morphology 272: 704–721.

James, P. S. B. R. 1975. A systematic review of the fishes of the family Leiognathidae. J. Mar. Biol. Ass. India 17 (1): 138–172.

Sparks, J. S., & P. Chakrabarty. 2015. Description of a new genus of ponyfishes (Teleostei: Leiognathidae), with a review of the current generic-level composition of the family. Zootaxa 3947 (2): 181–190.

Woodland, D. J., A. S. Cabanban, V. M. Taylor & R. J. Taylor. 2002. A synchronized rhythmic flashing light display by schooling Leiognathus splendens (Leiognathidae: Perciformes). Marine and Freshwater Research 53: 159–162.

Steatocranus gibbiceps, the Rapid River Bumphead

The cichlid fishes of the Great Lakes of Africa are rightly renowned as one of the world's most spectacular species radiations. Hundreds of species, occupying a wide range of ecological niches, have evolved in what is, geologically speaking, a short period of time. However, cichlids in Africa are not a phenomenon of the Great Lakes alone and many interesting species may be found in other parts of the continent, some of them belonging to local radiations of their own. Consider, for instance, the Congo River rapids endemic Steatocranus gibbiceps.

Male Steatocranus gibbiceps, copyright Polypterus.

The Congo is one of the largest African rivers with a drainage basin covering one-eighth of the continent (Schwarzer et al. 2011). Downstream of Kinshasa, the river gets funneled into an intermittently deep, narrow channel for a distance of some 300 km before broadening as it approaches the sea. The result is the world's longest stretch of river rapids. Many fish species are found only in this unique region of fast-flowing waters, among them multiple species of the cichlid genus Steatocranus including S. gibbiceps. The genus as a whole is restricted to the Congo basin; a single species previously recognised from the Volta River has since been transferred to its own genus (Weiss et al. 2019). The names Steatocranus and gibbiceps both basically mean the same thing: 'fat head', in reference to a fleshy swelling atop the fish's noggin. The exact size of this swelling varies between individuals, being most prominent in large males. Vernacular names given to Steatocranus species generally reflect this feature, such as bumphead cichlid or buffalo-head cichlid. Half a dozen species have been named within Steatocranus with several more being recognised but not yet formally described, most of them belonging to the radiation within the rapids. Schwarzer et al. (2012) found evidence for extensive historical cross-breeding between species and suggested that hybridisation may have been a significant factor in the genus' diversification.

Steatocranus gibbiceps is the largest species in this genus of moderately-sized fishes, growing up to about nine centimetres in length (Roberts & Stewart 1976). Its fast-current habitat is reflected in its slender body form. It is olive brown in coloration with the scales being light in colour at the centre and darker around the margins. Steatocranus gibbiceps is most clearly distinguished from other described species in its genus by its teeth: the front teeth of both the upper and lower jaws are conspicuously large and truncate. It also has a shorter gut than its congeners. This species appears to be specialised in feeding on freshwater snails which it scoops up and swallows whole, though it will take a broader range of food in captivity. Other species of Steatocranus mostly feed on algae.

Steatocranus species are not buoyant and tend to sit at the bottom of the water (Chase Klinesteker describes their behaviour as 'hopping around the bottom like a goby'). They escape the current by spending time in the hollows and crevices among rocks. Breeding happens within such hollows with dedicated pairs forming and females affixing their eggs to the rocks. Like many other cichlids, Steatocranus gibbiceps are dedicated parents after the eggs hatch. Tending of the fry is mostly the responsibility of the female while the male patrols the territory on the watch for danger. In this way, the baby bumpheads are given the best possible start at life.

REFERENCES

Roberts, T. R., & D. J. Stewart. 1976. An ecological and systematic survey of fishes in the rapids of the lower Zaïre or Congo River. Bulletin of the Museum of Comparative Zoology 147 (6): 239–317.

Schwarzer, J., B. Misof, S. N. Ifuta & U. K. Schliewen. 2011. Time and origin of cichlid colonization of the lower Congo rapids. PLoS One 6 (7): e22380.

Schwarzer, J., B. Misof & U. K. Schliewen. 2012. Speciation within genomic networks: a case study based on Steatocranus cichlids of the lower Congo rapids. Journal of Evolutionary Biology 25: 138–148.

Weiss, J. D., F. D. B. Schedel, A. I. Zamba, E. J. W. M. N. Vreven & U. K. Schliewen. 2019. Paragobiocichla, a new genus name for Gobiochromis irvinei Trewavas, 1943 (Teleostei, Cichlidae). Spixiana 42 (1): 133–139.

Of Hawks and Marble

The acanthomorph fishes (a major clade of fishes mostly characterised by the presence of spines at the front of the dorsal fin) have long been recognised as a particularly thorny problem for higher-level systematics. Morphological relationships between many of the large number of families recognised in this clade have been almost impossible to unravel, and it is only in recent years that molecular analyses have been able to start making sense of the rapid divergences. Nevertheless, there are some subgroups of the acanthomorphs that have been recognised for a long time and which recent analyses have continued to support. One such group is the cirrhitoids.

Spottedtail morwong Goniistius zonatus, copyright Joi Ito.

Variously referred to in recent sources as the Cirrhitoidea, the Cirrhitoidei, or the Cirrhitiformes, the cirrhitoids include about eighty known species usually divided between five families. These are the hawkfishes of the Cirrhitidae, the trumpeters and morwongs of the Latridae, the Cheilodactylus fingerfins, the Chironemus kelpfishes and the Aplodactylus marblefishes (the morwongs were historically placed with the fingerfins in the Cheilodactylidae but have recently been transferred based on molecular data—Ludt et al. 2019). The largest cirrhitoid is the dusky morwong Dactylophora nigricans of western and southern Australia, growing to 1.2 metres in length, but most species are only a fraction of this size. Some of the largest species are of note to fisheries. Cirrhitoids are generally inhabitants of reefs, mostly feeding on benthic invertebrates such as crustaceans. They have long been recognised as a coherent group owing to their distinctive fin structure. The lower rays of the pectoral fins are not branched, and in a number of species they are thickened and protrude past the fin membrane (observant readers of this post may have already noticed a theme in many of the genus names given to cirrhitoids, relating to this feature). The pelvic fins are set well behind the pectoral fins. Other notable features of the clade include a relatively high number of vertebrae, a relatively low number of rays in the caudal fin, and the presence in juveniles of a fatty sac running along the fish's underside (Greenwood 1995).

Coral hawkfish Cirrhitichthys oxycephalus, copyright Aquaimages.

Both morphological and molecular studies have agreed that the hawkfishes of the Cirrhitidae represent the sister clade to the remaining cirrhitoids. Hawkfishes are brightly coloured inhabitants of the tropics, usually well under a foot in length. They are distinguished by bundles of trailing filaments emerging from the ends of the spines on the dorsal fin. Perhaps the most familiar member of the group is the longnose hawkfish Oxycirrhites typus, a regular in marine aquaria. However, this is also perhaps the most atypical member of the family as other species do not have the elongate snout. Hawkfishes commonly perch atop corals on the uppermost part of the reef, protected by the coral's sting and able to maintain a clear view of their surrounds. Wikipedia suggests that this behaviour is the inspiration for the name of 'hawkfish', but I'm not sure I buy this. I mean, it sounds plausible, but it also sounds like the sort of thing you would have to be diving below the reef to see. Vernacular names for fish tend to more often refer to things you might observe while hauling them onto a boat.

Marblefish Aplodactylus arctidens, copyright Peter Southwood.

The remaining cirrhitoids are all found in cooler waters, mostly in the Southern Hemisphere. Two species of Latridae, the redlip morwong Goniistius zebra and the spottedtail morwing G. zonatus, are found in the northern Pacific off the coast of eastern Asia (the kind of distribution shown by the genus Goniistius, where species are found in northern and southern temperate waters but not in the intervening tropics, is known as 'anti-tropical' and it's an interesting question how such a distribution would come to be). They are mostly found among rocky reefs, with the kelpfishes Chironemus and marblefishes Aplodactylus being particularly associated with patches of seaweed. The marblefishes feed on algae (particularly reds) as well as on some invertebrates and are characterised by a transverse mouth that is little or not protractible (Regan 1911). As noted above, the family Latridae has been inflated recently by the inclusion of most of the species previously included in the Cheilodactylidae. Cheilodactylus itself is now restricted to two species found around southern Africa. They differ from the remaining species in the latrids by the absence of a gas bladder as well as by elements of the skeleton. Many of the latrids are favourites of anglers, being well regarded as eating fish. By contrast, the herbivorous marblefishes are maligned as very poor fare and avoided. There's something to be said for eating your greens.

REFERENCES

Greenwood, P. H. 1995. A revised familial classification for certain cirrhitoid genera (Teleostei, Percoidei Cirrhitoidea), with comments on the group's monophyly and taxonomic ranking. Bulletin of the Natural History Museum of London (Zoology) 61 (1): 1–10.

Ludt, W. B., C. P. Burridge & P. Chakrabarty. 2019. A taxonomic revision of Cheilodactylidae and Latridae (Centrarchiformes: Cirrhitoidei) using morphological and genomic characters. Zootaxa 4585 (1): 121–141.

Nelson, J. S., T. C. Grande & M. V. H. Wilson. 2016. Fishes of the World 5^th ed. Wiley.

Regan, C. T. 1911. On the cirrhitiform percoids. Journal of Natural History, series 8, 7: 259–262.

Tuskfish

The reefs of the Indo-west Pacific Oceans are one of the most species-rich regions of the entire marine environment. A complex geological history and high geographical complexity have contributed to drive speciation, resulting in a number of local radiations. One such radiation is the tuskfishes of the genus Choerodon.

Orange-dotted tuskfish Choerodon anchorago, copyright Bernard Dupont.

Choerodon is a genus of the wrasse family Labridae, most diverse around the islands of south-east Asia and northern Australasia where they inhabit coastal reefs or sea-grass beds. A revision of the genus by Gomon (2017) recognised 27 species, varying in size from a little over ten centimetres in length to half a metre or more. LIke other members of the wrasse family, they are often brightly coloured, with juveniles in particular of a number of species being patterned with bold vertical stripes. The vernacular name of 'tuskfish', as well as the zoological name of the genus (which translates as 'pig-tooth'), refers to the possesion of a pair of prominent, protruding incisors at the front of each of the upper and lower jaws. Other characteristic features of Choerodon include a dorsal fin with twelve spiny rays and eight soft rays, or thirteen spines and seven soft rays, and a lack of scales on the lower part of the cheek and lower jaw. Choerodon species, like most other wrasses, are protogynous hermaphrodites, starting their lives as females before eventually transforming into males.

Baldchin groper Choerodon rubescens, copyright Katherine Cure.

Diet-wise, tuskfishes are predators, feeding on animals such as crustaceans or mollusks. Larger species may even take other vertebrates. A kind of tool use has been observed for the genus, with difficult prey such as clams (Jones et al. 2011) or young turtles (Harborne & Tholan 2016) being grasped in the mouth and hammered against rocks to subdue them and/or break open shells. Multiple species of tuskfish may be found in close proximity though they will often differ in their preferred habitat. A study of five Choerodon species found around Shark Bay in Western Australia by Fairclough et al. (2008) found that the baldchin groper C. rubescens was found only on exposed marine reefs whereas the other four species preferred more sheltered habitats further inside the bay. The blue tuskfish C. cyanodus and blackspot tuskfish C. schoenleinii were both found in a range of habitats in this region but C. cyanodus was most abundant along rocky shores whereas C. schoenleinii preferred coral reefs (C. schoenleinii also differed from other species in the region in constructing burrows at the base of reefs that it used as a retreat). The purple tuskfish C. cephalotes was almost exclusively found among seagrass meadows. Finally, the bluespotted tuskfish C. cauteroma spent the early part of its life among seagrasses but moved onto reefs as it matured to adulthood.

Tuskfish and other wrasses are highly prized as eating fishes. However, it would be remiss to refer to the reefs of the Indo-west Pacific without mentioning that many of them are highly endangered. Heavy fishing, often using destructive methods, have combined with the effects of changing climate to cause a dramatic reduction in reef cover in recent decades. Should the decline continue at current rates, the lives of millions of people stand to be dangerously impacted.

REFERENCES

Fairclough, D. V., K. R. Clarke, F. J. Valesini & I. C. Potter. 2008. Habitat partitioning by five congeneric and abundant Choerodon species (Labridae) in a large subtropical marine embayment. Estuarine, Coastal and Shelf Science 77: 446–456.

Gomon, M. F. 2017. A review of the tuskfishes, genus Choerodon (Labridae, Perciformes), with descriptions of three new species. Memoirs of Museum Victoria 76: 1–111.

Harborne, A. R., & B. A. Tholan. 2016. Tool use by Choerodon cyanodus when handling vertebrate prey. Coral Reefs 35: 1069.

Jones, A. M., C. Brown & S. Gardner. 2011. Tool use in the tuskfish Choerodon schoenleinii? Coral Reefs 30 (3): 865.

Strike up the Bandfish

The diversity of fishes can be absolutely overwhelming and, as a result, there a some distinctive groups that fail to get their time in the spotlight. For this post, I'm briefly highlighting one of the lesser-known fish families, the bandfishes of the Cepolidae.

Australian bandfish Cepola australis at home in its burrow, copyright Rudie H. Kuiter.

Cepolids are small fish (growing to about 40 cm at most with many species much smaller) that are widespread in the eastern Atlantic and the Indo-Pacific but nowhere common. They have a laterally compressed, tapering body and a lanceolate caudal (tail) fin. They have an angled mouth that is relatively large compared to their size and pelvic fins with a single spine and five segmented rays, four of which are branched (Smith-Vaniz 2001). Two subfamilies are recognised, the Cepolinae and Owstoniinae. The Cepolinae are particularly elongate in body form and have the dorsal and anal fins connected by membranes to the caudal fin; these three fins are all distinctly separate in the Owstoniinae. Cepolines are divided between two genera: Acanthocepola species have scaly cheeks and spines on the preopercular margin whereas Cepola have naked cheeks and no such spines. Classification of Owstoniinae has been a bit less settled. A recent revision of the subfamily recognised only a single genus Owstonia (Smith-Vaniz & Johnson 2016), synonymising the genus Sphenanthias previously distinguished by features of the lateral line. As an indication of how little-known cepolids are, Smith-Vaniz & Johnson's revision more than doubled the number of known species of owstoniine from fifteen to 36 .

Male Owstonia hawaiiensis, from Smith-Vaniz & Johnson (2016).

Cepolids are most commonly found in relatively deep water, up to about 475 m. They are not targeted by any significant fisheries though Wikipedia claims that the oldest known recipe from a named author is for the cooking of bandfish. Cepolinae live on sandy or muddy bottoms on continental shelves where they excavate burrows in which they insert themselves with the head protruding above the substrate. Owstonia species are free-swimming, more commonly found near rocky bottoms on upper slopes or around atolls. The diet, where known, appears to be composed of zooplankton though Smith-Vaniz & Johnson (2016) suggested on the basis of tooth morphology that Owstonia were detritivores for at least part of their life cycle.

REFERENCES

Smith-Vaniz, W. F. 2001. Cepolidae. Bandfishes. In: Carpenter, K. E., & V. H. Niem (eds) FAO Species Identification Guide for Fishery Purposes. The Living Marine Resources of the Western Central Pacific vol. 5. Bony fishes part 3 (Menidae to Pomacentridae) pp. 3331–3332. Food and Agriculture Organization of the United Nations: Rome.

Smith-Vaniz, W. F., & G. D. Johnson. 2016. Hidden diversity in deep-water bandfishes: review of Owstonia with descriptions of twenty-one new species (Teleostei: Cepolidae: Owstoniinae). Zootaxa 4187 (1): 1–103.

Sweepers

It's time to meet the sweepers.

Smallscale bullseyes Pempheris compressa, copyright John Turnbull.

Sweepers, Pempheridae, are a group of moderately sized marine fish (usually about fifteen to twenty centimetres in length) found around tropical reefs in the Indo-Pacific and western Atlantic. I don't know why they're called sweepers, but in some areas they may be among the most abundant fish on the reef. Distinctive features of the group include a short, high dorsal fin and a long anal fin. The lateral line is also distinctively long, extending past the end of the tail right onto the caudal fin. Perhaps the feature that most stands out about sweepers is their large eyes. The eyes are so big because sweepers are nocturnal; during the day they retreat into protected crevices and caves, emerging at night to feed on minute crustaceans and other small animals (Mooi 2001).

Pygmy sweeper Parapriacanthus ransonneti, from here.

Sweepers are divided between two quite distinct genera. Members of the genus Parapriacanthus have a more 'average fish-like' elongate profile with the body less deep than the head is long. The other genus, Pempheris, has a distinctively deep profile, deeper than the head is long. The exact number of species of pempherid appears to still be uncertain. Pempherids lack the striking markings of other tropical fish and species can appear very similar to each other. What is more, they have two layers of scales on the body, with the outer scales being larger than the inner and deciduous (easily shed), and loss of the outer scales has the potential to change an individual's superficial appearance. Early descriptions of pempherid species are often inadequate for their reliable identification, and new species continue to be described at a quite rapid pace. A recent publication by Randall & Victor (2015), for instance, described no less than thirty-four new species of Pempheris from various locations in the Indian Ocean, close to doubling the number of species in the genus at a stroke. The genus Parapriacanthus is much less diverse, with only about five recognised species.

Orange-striped bullseyes Pempheris ornata in hiding during the day, copyright Peter Southwood.

Because of their relatively small size and retiring habits, sweepers are mostly not that significant economically. At least one species, Pempheris xanthoptera, is fished off the coast of Japan and mostly eaten as fish paste; it is supposed to be quite tasty. Some have appeared in aquaria.

When foraging at night, sweepers communicate with each other by producing popping noises through muscular flexing of the swim bladder wall. Noise production increases in the presence of potential threats, perhaps to warn other members of the school. At least some pempherid species also have bioluminescent glands associated with the posterior part of the gut. The bioluminescent compound is not directly produced by the fish itself but obtained by consuming bioluminescent ostracods. I haven't found whether the function of this bioluminescence is specifically known for pempherids, but similar ventral glows in other fish provide camouflage by breaking up the fish's silhouette when seen from below.

REFERENCES

Mooi, R. D. 2001. Pempheridae. Sweepers (bullseyes). FAO Species Identification Guide for Fishery Purposes. The Living Resources of the Western Central Pacific vol. 5. Bony fishes part 3 (Menidae to Pomacentridae) pp. 3201–3204. Food and Agriculture Organization of the United Nations: Rome.

Randall, J. E., & B. C. Victor. 2015. Descriptions of thirty-four new species of the fish genus Pempheris (Perciformes: Pempheridae), with a key to the species of the western Indian Ocean. Journal of the Ocean Science Foundation 18: 77 pp.

Leucicorus: FAKE EYES!

In an earlier post, I told you about the fishes known as brotulas. These are one of the most prominent groups of fish in the deep sea. They tend not to be attractive fish: their lack of outstanding dorsal and tail fins makes them look like something between an eel and a cod, and like many deep-sea fishes they look somewhat flabby and lumpish. There are numerous genera of brotulas out there; the individual in the photo below represents the genus Leucicorus.

Leucicorus atlanticus, from Okeanos Explorer.

Leucicorus belongs to the brotula family Ophidiidae, commonly known as the egg-laying brotulas though Leucicorus' own reproduction has (so far as I have found) not been directly observed. The feature that most immediately sets Leucicorus apart from other brotulas is the eyes: Leucicorus species have very large eyes but the actual lenses are rudimentary or absent (Cohen & Nielsen 1978). It almost looks like they grew bigger and bigger to cope with the low light of the deep sea before they just kind of gave up at some point.

Two species of Leucicorus are currently recognised, each known from separate parts of the world. Leucicorus lusciosus is found in the eastern Pacific, whereas L. atlanticus is known from around the Caribbean. The two species differ in meristic characters and proportions: for instance, L. lusciosus has more dorsal and anal fin rays, but fewer vertebrae and gill rakers, and has a deeper body (Nielsen & Møller 2007). Leucicorus has also been found in the vicinity of the Solomon Islands, but interestingly enough Nielsen & Møller (2007) identified the specimen found as L. atlanticus rather than L. lusciosus, despite the latter species' more proximate distribution. One wonders if perhaps a third species is involved, yet to be recognised.

REFERENCES

Cohen, D. M., & J. G. Nielsen. 1978. Guide to identification of genera of the fish order Ophidiiformes with a tentative classification of the order. NOAA Technical Report NMFS Circular 417.

Nielsen, J. G., & P. R. Møller. 2007. New and rare deep-sea ophidiiform fishes from the Solomon Sea caught by the Danish Galathea 3 Expedition. Steenstrupia 30 (1): 21–46.

The Violet Demoiselle

Meet the violet demoiselle Neopomacentrus violascens (shown above in a photo by J. E. Randall). This little fish (adults get up to about 7.5 cm in length) is found in tropical waters of the western Pacific, from Japan in the north, south and east to northern Australia and Vanuatu. They usually associate in large schools around inshore reefs, and can commonly be found hanging around outcropping structures over soft bottoms such as coral or rocky outcrops, or wharf pilings (Koh et al. 1997). Violet demoiselles feed on small plant or animal plankton, such as copepods or algae.

The genus this species belongs to, Neopomacentrus, is one of the more recently recognised genera of the damselfish family Pomacentridae. It is similar to two larger genera in the family, Abudefduf and Pomacentrus, but differs from the former in having the hind margin of the preopercle (the anterior one of the bones making up the operculum or gill cover) crenulate or serrate rather than smooth. Pomacentrus has a similar preopercle, but has the suborbital region at least partially naked whereas Neopomacentrus has that region entirely scaly. Neopomacentrus violascens has a distinctive colour pattern, which is mostly a purplish brown, with bright yellow on the caudal fin and the rear of the dorsal fin.

According to Fishbase, individuals of this species form pairs when mating, and the females lay eggs that sink to the bottom and stick to the substrate. The eggs are then guarded and aerated by the males. I have come across reference to this species having been bred in captivity though I get the impression that they are not one of the most commonly kept aquarium fish. This may be because they are somewhat dull in coloration compared to related species, and they are fairly retiring in character. A recent blog post at Zoo Volunteer noted that damselfish species are rarely bred commercially due to the difficulty of providing suitable conditions. Instead, the market for species of this family is usually supplied with wild-caught individuals, commonly collected through the use of cyanide to essentially suffocate the fish until they lose conciousness. Not particularly pleasant for the fish, and arguably not that pleasant for the aquarist either as fish obtained in this method tend to have a much reduced lifespan.

REFERENCES

Koh, J. R., J. G. Myoung & Y. U. Kim. 1997. Morphological study on the fishes of the family Pomacentridae. I. A taxonomical revision of the family Pomacentridae (Pisces; Perciformes) from Korea. Korean Journal of Systematic Zoology 13 (2): 173–192.

Fishes be Crazy

Despite how it may look, there is absolutely nothing wrong with this fish. Butis butis is a moderately sized species of fish (up to about 14 cm in length) widespread in warmer waters around the Indian and western Pacific Oceans. They are found in shallow bays and mangrove swamps, often entering into estuaries and lower reaches of rivers. It is known by a range of vernacular names, including crimson-tipped gudgeon or duckbill sleeper. In the aquarium trade, it often goes by the name of crazy fish, in reference to its distinctive habit of swimming hanging vertically head-down or even swimming upside-down. Its predilection for such unusual angles assists it in remaining concealed from both predators and prey; Ryan (1981) noted that the addition of anaesthetic for collection purposes to a pool resulted in the sudden appearance of several specimens of which no sign had been previously seen. Their camouflage abilities are further enhanced by the ability to change colour to a certain degree, from pale to dark. Butis butis are ambush predators of smaller fish and invertebrates that they engulf in their broad jaws with rapid lunges.

Drawing of Butis butis, coloured from an original in Herre (1927) by M. L. Nievera.

The genus Butis belongs among the gobies, a somewhat notorious group of fish from a taxonomic perspective. In the words of the South African ichthyologist J. L. B. Smith, "The Gobioid fishes are one of the major trials of ichthyologists, and when general regional collections are worked up, these fishes tend to be pushed aside, and are apparently often identified with some impatience by those not specially interested" (Smith 1958). This notoriety is mostly due to the small size of many gobies, together with a tendency to the reduction of diagnostic features. Earlier authors classified Butis within the Eleotridae, a group of gobies (commonly known as sleepers, presumably due to their benthic habits) distinguished by having the pelvic fins separate from each other (in other gobies, the pelvic fins are united into a ventral sucker or disc). This, however, is a primitive feature only, and more recent molecular phylogenies have confirmed the paraphyly of Eleotridae in the broad sense. As a result, Butis and some of its nearest and dearest have been separated out into a separate family Butidae (Thacker 2011). However, while the separation of Eleotridae and Butidae seems to be fairly widely accepted, the two groups are still not clearly defined morphologically. Characteristic features of Butis relative to other gobies include (among others) the presence of a complete covering of scales, and a bony ridge above each eye (Smith 1958). In a number of species of the genus, including B. butis, the head is low and long, and the lower jaw distinctly protruding; however, the mudsleeper B. koilomatodon has a shorter, rounder head (this latter species, though originally native to a similar range to B. butis, has become invasive in more recent years in west Africa and Brazil, presumably carried in ballast water). Butis butis differs from other species in the genus in having small secondary scales at the base of most scales on the trunk, and the bony ridges above its eyes are more or less smooth (Herre 1927).

REFERENCES

Herre, A. W. 1927. Gobies of the Philippines and the China Sea. Philippine Bureau of Science Monographic Publications on Fishes 23: 1–352, 26 pls.

Ryan, P. A. 1981. Records of three new freshwater fishes from the Fiji Islands. Pacific Science 35 (1): 93–95.

Smith, J. L. B. 1958. The fishes of the family Eleotridae in the western Indian Ocean. Ichthyological Bulletin 11: 137–163.

Thacker, C. 2011. Systematics of Butidae and Eleotridae. In: Patzner, R. A., J. L. Van Tassell, M. Kovačić & B. G. Kapoor (ed.) The Biology of Gobies pp. 79–85. CRC Press.

In a Pufferfish's Garden

Bullseye puffer Sphoeroides annulatus, copyright Geoffrey W. Schultz.

I don't know if it applies in other parts of the world, but one animal that you are guaranteed to see in the estuary here in Perth is pufferfish. One of the most instantly recognisable fish families, pufferfish (Tetraodontidae) are of course famed for their high toxicity, the determination of some people to eat them despite aforementioned toxicity, and their habit of swallowing air or water when threatened to inflate their distendible bellies. That last feature makes them a favourite of children (or at least of yours truly as a child), because their slow swimming style makes them one of the few fish that can be easily captured by hand (you just have to make sure you don't allow the fish to give you a nasty bite with their beak). The first feature makes them a lot less popular with fishermen who have to experience the frustration of reeling in a line to find that the bait has been taken by a puffer, then trying to remove the puffer from the hook while avoiding the aforementioned beak.

Oceanic puffer Lagocephalus lagocephalus, from Baino96.

There are a little under 200 known pufferfish species worldwide. Most of them are found in coastal marine and brackish waters, but there are also several species found in fresh water in South America, Africa and southeast Asia. Some marine species are also resistant to fresh water and may spend extended periods away from the sea. Some southeast Asian brackish-water Tetraodon species even make regular appearances in the the aquarium trade labelled as 'freshwater' puffers (Yamanoue et al. 2011), though their long-term survival requires more appropriate water conditions. The toxin associated with pufferfishes is not produced by the fish itself, but accumulated through its diet. As such, the exact level of toxicity of a pufferfish may vary according to season.

Grass puffer Takifugu niphobles, copyright OpenCage.

A molecular phylogenetic analysis of pufferfish by Yamanoue et al. (2011) identified four main clades in the family. These clades were also supported by a subsequent analysis by Santini et al. (2013), though the deeper relationships between the clades differed between the analyses. Yamanoue et al. (2011) identified a small number of freshwater clades (only one for each continent with freshwater taxa) and inferred that the transition from marine to fresh water had happened only rarely. Santini et al. (2013), in contrast, supported a higher number of transitions in tetraodontid history, though at least some of the difference between the two studies can be explained by differing definitions of 'freshwater'. For instance, some species of Takifugu usually live in brackish water but spawn in fresh water; Santini et al. counted these as freshwater species, but Yamanoue et al. did not.

Papuan toby Canthigaster papua, photographed by Dwayne Meadows.

One of the major clades identified within the Tetraodontidae includes the genus Lagocephalus, a group of relatively long-bodied puffers including some of the few pelagic puffer species. This genus may be the sister taxon of the remaining puffers (as found by Yamanoue et al.), or it may have a more nested position as sister to a clade including the mostly West Atlantic-East Pacific genera Sphoeroides and Colomesus (as found by Santini et al.). This latter clade includes South America's only freshwater puffer, the Amazon species Colomesus asellus. Santini et al. identified the basalmost tetraodontid clade as an Indo-West Pacific assemblage including the genus Takifugu and related taxa, which Yamanoue et al. had found as sister to the final clade including taxa related to the genus Tetraodon. This last clade includes the African and southeast Asian freshwater puffers (except for a few members of the Takifugu clade that cross into fresh water at times). It also includes the genus Canthigaster, the sharpnose pufferfish. In contrast to the more or less globular form of all other puffers, sharpnose puffers have a laterally compressed body form that superficially looks a bit more like a triggerfish than a puffer. Most Canthigaster species are reef-dwellers, a somewhat unusual habitat for a puffer (the other main group of reef-dwelling puffers being the genus Arothron, also in the Tetraodon clade).

Circular underwater 'nest' constructed by a pufferfish, from Spoon & Tamago.

One of the most remarkable characteristics of any puffer, though, was not discovered until quite recently. In 2012, it was announced that large structures observed off the coast of Japan by underwater photographer Yoji Ookata were in fact the work of pufferfish. These structures, circular and regular geometric patterns in the sea bed about 1.5 metres in diameter, were made by male puffers swimming against the sand. The structures are believed to function in attracting females, and also function as nests in which the females lay their eggs. Rather frustratingly, I haven't found any indication exactly which species of puffer is involved!

Puffer in the process of building a nest, also from Spoon & Tamago.

REFERENCES

Santini, F., M. T. T. Nguyen, L. Sorenson, T. B. Waltzek, J. W. Lynch Alfaro, J. M. Eastman & M. E. Alfaro. 2013. Do habitat shifts drive diversification in teleost fishes? An example from the pufferfishes (Tetraodontidae). Journal of Evolutionary Biology. doi: 10.1111/jeb.12112.

Yamanoue, Y., M. Miya, H. Doi, K. Mabuchi, H. Sakai & M. Nishida. 2011. Multiple invasions into freshwater by pufferfishes (Teleostei: Tetraodontidae): a mitogenomic perspective. PLoS ONE 6 (2): e17410. doi:10.1371/journal.pone.0017410.

Book Review: The Amazing World of Flyingfish, by Steve N. G. Howell

In June of last year, I was standing on the deck of a ferry in Taiwan, headed for the island of Lüdao (commonly known as Green Island), keeping an eye out for any interesting sights. I was particularly intrigued by the seabirds that I kept seeing flying away from the ferry. For some time, I couldn't make out exactly what kind of bird they were: they were small, and flew very quickly. Most oddly, they never seemed to rise very far above the water; I kept waiting for one to get higher so that I could get a better idea of its shape, but every time I tried to keep an eye on one individual, it would seem to disappear, as if it had re-entered the water. Eventually, understanding dawned: what I was seeing were not birds at all, but flying fish.

Flyingfish (Exocoetidae) are prominent members of the pelagic ecosystem in tropical waters. For some tropical seabirds (actual birds this time, such as boobies or frigatebirds), they are among the primary source of food. Steve Howell, author of The Amazing World of Flyingfish (Princeton University Press, who were kind enough to send me a review copy), put together a guide to flyingfish after travelling from New Zealand to Australia on the Spirit of Enderby as part of a cruise that was primarily supposed to be for bird-watching. But, as Howell explains, "birds tend to be few in the blue equatorial waters (remember, it's a desert, even though it's full of water), and attention sooner or later shifts to flyingfish".

The Amazing World of Flyingfish is not a large book: all up, it barely makes it over 50 pages. But almost every one of those pages is adorned with spectacular photographs that capture the grace and variety of flyingfish. The images chosen work wonders in expressing the liveliness of their subjects. My favourite image technically doesn't even show the fish at all: on p. 16, a triptych of photographs showing the process of re-entering the water shows first the fish in flight, then closing its fins as it approaches the water's surface, and then simply the splash as it disappears below. The text, geared towards a younger or a lay audience, provides a general overview of flyingfish, with chapters given self-explanatory titles such as, "What is a flyingfish?", "How big are they?", "How do they fly?"

And yet, I also found Howell's book frustrating. The numerous different flyingfish varieties depicted are labelled with vernacular names largely of his own creation, such as Atlantic patchwing, sargassum midget, Pacific necromancer. Zoological names are, for the most part, not provided. As Howell explains, most field guides to marine fish are written for biologists or fisherman, and are oriented around identifying a specimen after it has been caught, often relying on features (such as scale counts) that are not discernible in photographs of live individuals. As a result, the identity of most of Howell's 'field varieties' remains uncertain. But then, in another section of the book, we are told that one juvenile morph "was examined genetically and proved to be a young Atlantic Necromancer" (capitalisation Howell's), implying that the zoological identity of this species, at least, is known.

As Howell points out, "there remains an unfilled niche for a field guide that portrays flyingfish as observers see them in the air". Howell has produced an attractive and engaging introduction to the world of flyingfish, and it should provide an inspiration to fill that niche.

The Sweetest of Lips

Oblique-banded sweetlips Plectorhinchus lineatus, copyright Richard Ling.

In an earlier post on this site, I referred to a fish of the family Lethrinidae being known by the name of "sweetlips". However, as is usually the way with fish vernacular names, there is more than one family of fishes to which this name can be applied. 'Sweetlips' is also the vernacular name for fishes in the Plectorhinchinae.

The Plectorhinchinae is most commonly treated as a subfamily within the family Haemulidae, the grunts (some sources will place 'Plectorhynchidae' as a separate family, and no, that wasn't a typo: read on). Plectorhinchines are distinguished from other subfamily of haemulids, the Haemulinae, by characters including a longer dorsal fin and the presence of at least four prominent lateral line pores under the chin (Johnson 1980). The name 'sweetlips' refers to the prominent lips of mature individuals of two of the genera of plectorhinchines, Plectorhinchus and Diagramma, which are often a distinct colour from the rest of the head. Members of the third genus, Parapristipoma, have the lips not quite so prominent, and are commonly referred to as 'grunts' like the remaining haemulids.

African striped grunts Parapristipoma octolineatum, copyright Juan Cuetos.

The plectorhinchines are found around tropical reefs in the Indo-West Pacific and East Atlantic, with a single species, the rubberlip grunt Plectorhinchus mediterraneus, being found in the in the Mediterranean and Black Seas. No plectorhinchines are found on either side of the Americas. They are nocturnal predators of benthic invertebrates, emerging at night from the secluded crevices and overhangs where they spend the day. Most are medium-sized fish, though the painted sweetlips Diagramma pictum can get up to 90 cm. They are popular with fishers; Smith (1962) referred to them as "among the best if not the best eating fishes of the reef-haunting species". Many species can go through significant changes in coloration as they mature: spotted juveniles may become unicoloured adults, or blotchy babies may mature into stripes. The differences are great enough that juveniles and adults have often been mistaken for separate species.

Juvenile oriental sweetlips Plectorhinchus vittatus, copyright Jan Messersmith. The adult form of this species resembles the oblique-banded sweetlips in the top photo on this post.

But failure to associate parents with their children is not the only way in which this group has been dogged by confusing taxonomy. The name of the type genus has been variously spelled Plectorhinchus or Plectorhynchus, with the family name varying accordingly (it seems that 'Plectorhinchus' is the correct spelling). A surprising number of sources (e.g. Tavera et al. 2012) seem to have it both ways, with the genus being called Plectorhinchus but the higher taxon being called Plectorhynchinae (R. van der Laan et al. confirm the correct family-name spelling). Meanwhile, Smith (1962) argued for the use of the name Gaterin in place of Plectorhinchus, and called the family Gaterinidae. And if you have any interest in the vagaries of taxonomy, settle in: this is going to be a whole thing.

The name 'Gaterin' dates from what is usually known as Forsskål's (1775) Descriptiones animalium, which Fricke (2008) argued should be attributed to Niebuhr (see, right from the first sentence it's confusing). Peter Simon Forsskål and Carsten Niebuhr were members of a Danish scientific expedition in 1761 to 1763 to the Red Sea (though Forsskål himself was Swedish, but that's another story). Forsskål was the expedition's naturalist, while Niebuhr was there as a geographer. The history of the expedition, and of the composition of Descriptiones animalium, has been summarised by Fricke (2008). The expedition was particularly ill-fated; of six original members, Niebuhr was the only one to make it back to Denmark alive. After returning to Denmark, Niebuhr started preparing Forsskål's notes for publication. However, he found this no easy task. Forsskål had not prepared a single manuscript, but made notes on various scraps of paper; in the end, Niebuhr suspected that many of these scraps had gone missing. As an engineer, Niebuhr knew little Latin and even less biology, so he obtained the services of an academic adviser. The identity of this adviser was not divulged in the final publication by Niebuhr himself, but he has since been identified as the Danish naturalist Johann Christian Fabricius. The relationship between Niebuhr and Fabricius was not entirely positive (Niebuhr later stated that his adviser on Descriptiones animalium had been a 'strange fellow'), and Fabricius does not seem to have spent any more time on the Forsskål notes than he absolutely had to. As a result, the final publication that emerged was partly Forsskål, partly Niebuhr, partly Fabricius, and all dog's breakfast.

The name 'Gaterin' is listed by Forsskål/Niebuhr/Fabricius as one of the sub-divisions of the genus Sciaena, and Smith's (1962) revival of the name was based on the assumption that Forsskål intended these subdivisions to represent what we would now call subgenera. As such, Gaterin published in 1775 would clearly be an earlier name than Plectorhinchus published in 1802. Smith further supported this interpretation by pointing out that two names listed by 'Forsskål' as subdivisions of Chaetodon, Acanthurus and Abudefduf, had since been widely accepted as names for separate fish genera. There were no grounds, he claimed, for taking Abudefduf as valid but refusing Gaterin.

As it happens, Forsskål probably never intended either Gaterin or Abudefduf to represent generic names of any kind. It seems that his notes had used local Arabic names to refer to taxa to which he had not yet supplied formal Latin names. When Fabricius compiled these notes, he simply used the Arabic names as formal names, probably because he just didn't care. When 'Forsskål' referred to 'Gaterin' in his introductory paragraph for Sciaena, he was probably referring to the individual species known in Arabia as gaterin rather than any formal group. 'Abudefduf' may have been similarly inadvertent, but long usage as a genus name means that it should probably be retained whatever its original status. No such argument can be marshalled in favour of 'Gaterin', whose usage in place of Plectorhinchus has been minimal.

And I can think of no better response to all that than the expression of this painted sweetlips Diagramma pictum. Copyright John Natoli.

REFERENCES

Fricke, R. 2008. Authorship, availability and validity of fish names described by Peter (Pehr) Simon Forsskål and Johann Christian Fabricius in the ‘Descriptiones animalium’ by Carsten Niebuhr in 1775 (Pisces). Stuttgarter Beiträge zur Naturkunde A, Neue Serie 1: 1–76.

Johnson, G. D. 1980. The limits and relationships of the Lutjanidae and associated families. Bulletin of the Scripps Institution of Oceanography 24: 1–114.

Smith, J. L. B. 1962. Fishes of the family Gaterinidae of the western Indian Ocean and the Red Sea with a resume of all known Indo Pacific species. Ichthyological Bulletin 25: 469-502.

Tavera, J. J., A. Acero P., E. B. Balart & G. Bernardi. 2012. Molecular phylogeny of grunts (Teleostei, Haemulidae), with an emphasis on the ecology, evolution, and speciation history of New World species. BMC Evolutionary Biology 12: 57. http://www.biomedcentral.com/1471-2148/12/57.

Sleepers

Hawaiian sleeper Eleotris sandwicensis, from the Hawaii Biological Survey.

Fishes of the genus Eleotris are a group of gobioids commonly known as the spinycheek sleepers. I haven't found a definite statement as to why they're called sleepers, but presumably it's because, as sit-and-wait ambush predators, they spend a lot of time lying around on the bottom. Eleotris species are found in tropical and subtropical waters around the world, mostly in estuaries and freshwater. They are smallish fish, with most species seeming to be in the ten to twenty centimetre size range. The 'spinycheek' part of the vernacular name refers to the presence of a hook-like spine on the lower corner of the preoperculum (the bone running between the cheek and the gill cover on the side of the head). This spine may be covered with tissue and so not always readily visible, but Pusey et al. (2004) note that it 'can be easily detected by running a thumbnail lightly, and carefully, along the preoperculum margin'. Carefully, I think, is the operative word here.

Eleotris oxycephala, from Chinese Academy of Fishery Sciences.

The species of Eleotris are mostly a conservative bunch appearance-wise, and the genus seems to have gotten a reputation for being difficult to work with taxonomically (it doesn't help matters that for a long time 'Eleotris' was something of a dumping ground for generalised gobioids). The Japanese species were revised in 1967 by Akihito (yes, that Akihito), the West African species have been revised by Miller (1998), and the North and South American species by Pezold & Cage (2002), but species from the remainder of the Indo-Pacific remain unrevised. There has been some disagreement over the status of a group of New World species classified in the genus Erotelis, which resemble Eleotris species but are generally more elongate and have higher numbers of fin rays (Pezold & Cage 2002). Miller (1998) felt that this genus should be synonymised with Eleotris, but Pezold & Cage (2002) argued that its members were distinct enough to be kept separate. A molecular phylogenetic analysis of the gobioids by Thacker & Hardman (2005) suggested that 'Erotelis' is nested within Eleotris, which may support their synonymisation.

Dusky sleeper Eleotris fusca, photographed by C. Appleby.

The sleepers are amphidromous, meaning they spend part of their life in the sea. Sleepers enter the sea as larvae, returning to fresher waters as they mature. As a result of this marine stage in the life cycle, individual species of Eleotris may be widespread and can often be found in places such as oceanic islands that lack populations of permanently freshwater species. It has even been suggested they may cross oceans: Miller (1998), noting similarities between species on either side of the Atlantic, suggested that this may be the result of trans-Atlantic dispersal. Among the evidence cited in favour of this possibility was the record in 1987 of a specimen of the northern South American species Eleotris pisonis from the island of St Helena in the mid-Atlantic. However, Miller also noted that the amount of time it would take to disperse across the Atlantic is greater that the time it would take for the larva to develop to maturity (and mature Eleotris are not known from the open sea). Pezold and Cage (2002) were more skeptical about the possibility of trans-Atlantic dispersal, even though they admitted to being unable to identify any characters distinguishing the Caribbean E. amblyopsis from the West African E. daganensis. They queried whether the St Helena record may have been an individual transported in ship ballast water, rather than an unaided dispersal.

REFERENCES

Miller, P. J. 1998. The West African species of Eleotris and their systematic affinities (Teleostei: Gobioidei). Journal of Natural History 32 (2): 273-296.

Pezold, F., & B. Cage. 2002. A review of the spinycheek sleepers, genus Eleotris (Teleostei: Eleotridae), of the western hemisphere, with comparison to the West African species. Tulane Studies in Zoology and Botany 31: 19–63.

Pusey, B., M. Kennard & A. Arthington. 2004. Freshwater Fishes of North-eastern Australia. CSIRO Publishing: Collingwood.

Thacker, C. E., & M. A. Hardman. 2005. Molecular phylogeny of basal gobioid fishes: Rhyacichthyidae, Odontobutidae, Xenisthmidae, Eleotridae (Teleostei: Perciformes: Gobioidei). Molecular Phylogenetics and Evolution 37: 858-871.

Into the Labyrinth

Climbing perch Anabas testudineus emerging from water, as illustrated by Richard Lydekker.

Amongst the unholy mess that is the Percomorpha, one group that has long been recognised is the labyrinth fishes of the Anabantoidei. The anabantoids are a group of freshwater fishes found in southern Asia and Africa (but not Madagascar) that get their vernacular name from their possession of a distinctive respiratory organ called the labyrinth. This organ, found in a cavity above the gills, is derived from part of the first gill arch; the bone has become expanded and much-folded, and is covered with a layer of respiratory epithelium. So long as the gills do not actually dry out, the labyrinth allows these fish to take in oxygen directly from the air, and they can survive in warm, low-oxygen waters. They can even survive for limited periods entirely out of water (a feature that has helped make some of the larger species popular food fish, due to the greater ease of keeping them fresh in a tropical environment). Recent phylogenetic studies (e.g. Li et al. 2009) have agreed in placing labyrinth fishes as related to a number of other freshwater Indo-Australian fishes, such as the snakeheads of the Channidae and the swamp eels of the Synbranchidae, many of which are also tolerant of air-breathing.

Kissing gouramis Helostoma temminckii, from Peter Bus.

Labyrinth fishes can be divided between three families (Rüber et al. 2006). One of these contains a single species, the kissing gourami Helostoma temminckii of south-east Asia. Kissing gouramis are primarily specialised filter feeders, though they may also graze on algae or insects. The vernacular name refers to their enlarged lips, making them look permanently puckered up. Kissing gouramis even 'kiss', pressing their smackers against one another, though this is regarded as an act not of affection but of aggression (kind of like a 1930s Hollywood melodrama) as the fish push against one another.

A rather unfortunate Cape kurper Sandelia capensis, photographed by Darryl Lampert.

The climbing perches of the Anabantidae include the south Asian Anabas and the African Ctenopominae. These short-bodied carnivores have serrated edges to their gill covers that the Asian species use to pull themselves over land when travelling between water bodies (imagine lying on your stomach and pulling yourself along with your chin). You can see video of some climbing perch Anabas testudineus emerging from water here.

Giant gourami Osphronemus goramy, photographed by E. Naus.

The most diverse subgroup of the Anabantoidei is the gouramis of the Osphronemidae, another south Asian group. The largest of the Osphronemidae, the giant gourami Osphronemus goramy, grows up to 70 cm, but most species are quite a bit smaller. A number of gourami species (as well as the kissing gourami) are popular aquarium fishes; the most popular by far is the Siamese fighting fish Betta splendens, males of which have been bred to exhibit much longer and more ornamental fins than found in the wild. The gouramis are generally omnivorous, with species varying in the extent to which they prefer plant or animal food. The most specialised carnivore of the Osphronemidae is the pikehead Luciocephalus pulcher, a small but elongate species that has been described as having the most protrusible mouth of any fish (and that, by the way, is no small claim). You can see the pikehead in action below:

The pikehead is so divergent from other labyrinth fishes that past authors have regarded it as its own family, possibly the sister taxon to all other anabantoids, or even questioned whether it was a labyrinth fish at all. However, as confirmed by Rüber et al. (2006), Luciocephalus is not only a true anabantoid but nested well within the Osphronemidae as sister to the chocolate gouramis of the genus Sphaerichthys. These and two other genera, Ctenops and Parasphaerichthys, form what is known as the 'spiral egg' clade, named after the presence of spiraling ridges on the egg leading to the micropyle, that have been suggested to act as guides for the sperm.

Siamese fighting fish Betta splendens mating below a bubble-nest, photographed by Stephen & John Downer.

The anabantoids are also known for the bubble-nests constructed by a number of species, in which the eggs are contained within a floating nest of bubbles that is guarded by the male parent (both parents in the Ceylonese combtail Belontia signata). Bubble-nesting has evolved at least twice among the anabantoids: once in the Osphronemidae, and once in the ctenopomine genus Microctenopoma (other anabantids and Helostoma are free spawners that do not construct nests or guard their eggs; the ctenopomine Sandelia capensis digs a nest in the bottom substrate) (Rüber et al. 2006). Though bubble-nesting is probably the ancestral behaviour for Osphronemidae, it has been modified in a number of sublineages. Osphronemus species build submerged nests from vegetation, while members of the 'spiral egg' clade (except Parasphaerichthys) and a number of Betta species are mouthbrooders. Usually the male broods the fry in these species, but the female is the brooder in a couple of Sphaerichthys species.

REFERENCES

Li, B. A. Dettaï, C. Cruaud, A. Couloux, M. Desoutter-Meniger & G. Lecointre. 2009. RNF213, a new nuclear marker for acanthomorph phylogeny. Molecular Phylogenetics and Evolution 50: 345-363.

Rüber, L., R. Britz & R. Zardoya. 2006. Molecular phylogenetics and evolutionary diversification of labyrinth fishes (Perciformes: Anabantoidei). Systematic Biology 55 (3): 374-397.

Empire of the Sunfish

Do you remember when this particular nightmare was vomited forth from the jaws of pop culture hell?


Yes, this was the execrable Billy the Bass, just one more reason we can all be glad that the 90s aren't around any more. But what was it supposed to be?

Smallmouth bass Micropterus dolomieu, photographed by Eric Engbretson.

The bass and sunfishes of the family Centrarchidae are a group of more than thirty species of freshwater fish mostly native to North America east of the Rocky Mountains. A single species, the Sacramento perch Archoplites interruptus, is native to northern California. The family was more widely distributed in the past: the Oligocene–Miocene genera Plioparchus and Boreocentrarchus hail from Alaska, Oregon and the Dakotas (Near & Koppelman 2009). They will also be much more widely distributed in the future: species of the genera Lepomis and Micropterus have been introduced to numerous places around the world as sportfish. The centrarchids are all carnivorous, though the nature of their prey varies from zooplankton to insects to other fish.

White crappie Pomoxis annularis, photographed by D. Ross Robertson.

The molecular analysis of the Centrarchidae by Near et al. (2005) identified the mud sunfish Acantharchus pomotis as sister to all other centrarchids, contrary to its previous inclusion in the subfamily Centrarchinae with other centrarchids possessing more than three spines in the anal fin (Near & Koppelman 2009). Instead, the two genera whose species possess only three anal spines, Lepomis and Micropterus, form a clade that is sister to the remaining 'centrarchine' genera. These are the aforementioned Archoplites, the flier Centrarchus macropterus, the banded sunfishes Enneacanthus, the rock basses Ambloplites and the somewhat unfortunately named crappies of the genus Pomoxis. These are mostly deep-bodied feeders on small invertebrates, though the larger species may also take small fish. Archoplites is a more dedicated piscivore. This latter species is also notable for having less elaborate mating behaviour than other centrarchids: in contrast to the elaborate courtship rituals and nests of other centrarchids, Archoplites males do little more than use the tail fin to dig a small depression (Berra 2007). One can't resist wondering if Archoplites' lax behaviour is connected with its geographic isolation from other species.

Pumpkinseed Lepomis gibbosus, photographed by Cliff.

The genera Micropterus and Lepomis are each more diverse than the centrarchine genera. The black basses of the genus Micropterus are relatively long-bodied compared to other centrarchids, and are all piscivores. Lepomis, with twelve species, is the most diverse centrarchid genus both numerically and ecologically; as well as numerous insectivorous species, it contains the piscivorous warmouth Lepomis gulosus, the specialised planktivorous bluegill L. macrochirus, and two molluscivorous species, the redear sunfish L. microlophus and the pumpkinseed L.gibbosus. Phylogenetic relationships within Lepomis indicate a certain dynamism of ecology as well: a number of species pairs can be identified connecting large and small species, while the two molluscivores are not immediate relatives within the genus (Near et al. 2005).

REFERENCES

Berra, T. M. 2007. Freshwater Fish Distribution. University of Chicago Press.

Near, T. J., D. I. Bolnick & P. C. Wainwright. 2005. Fossil calibrations and molecular divergence time estimates in centrarchid fishes (Teleostei: Centrarchidae). Evolution 59 (8): 1768-1782.

Near, T. J., & J. B. Koppelman. 2009. Species diversity, phylogeny and phylogeography of the Centrarchidae. In: Cooke, S. J., & D. P. Philipp (eds) Centrarchid Fishes: Diversity, biology and conservation, pp. 1-38. Blackwell Publishing.

The Live-Bearing Brotulas

Black brotula Stygnobrotula latebricola, photographed by Thomas W. Doeppner.

The subject of today's post is the Bythitidae, a family of mostly marine fishes referred to as the live-bearing brotulas. Bythitids belong to the Ophidiiformes, a group of more or less elongate fishes with long soft dorsal and anal fins. They differ from most other ophidiiforms in that the males have an external intromittent organ and they are mostly live-bearers rather than egg-layers (though at least one species, Didymothallus criniceps, is potentially an egg-layer: Schwarzhans & Møller 2007). Bythitids do share these features with the deep-water Aphyonidae, which are however particularly elongate, lack scales and a swim bladder, and have loose translucent skin in contrast to the firm skin of bythitids (Nielsen et al. 1999).

Bahamian cave fish Lucifuga spelaeotes, photographed by Joe Dougherty.

Bythitids are often thought of as deep-water fishes, but there is also a reasonable diversity of them in shallower habitats such as coral reefs. The shallower-living species are mostly very cryptic in their habits and may be only rarely encountered; deeper-water species may occupy more open habitats or be found in association with hydrothermal vents. Some species of the genera Lucifuga and Ogilbia are found in freshwater caves in the Caribbean (Lucifuga species), the Yucatan (Ogilbia pearsei) and the Galapagos (O. galapagosensis); other species are found in marine caves such as the 'blue holes' of the Bahamas. New species of bythitid continue to be described at a reasonable rate of knots (over 100 species have been described in the last ten years alone). They vary in size from small (Microbrotula species are about four centimetres in length) to very large (Cataetyx laticeps reaches over 75 cmm; the Fishes of Australia website states that bythitids grow up to 2 m, but I haven't been able to find which species this refers to).

Yellow cuskeel Dinematichthys iluocoeteoides, from here.

Because of their cryptic habits, the lifestyles of most bythitids remain poorly known. They are predators of invertebrates and other fish. The few identified larvae have been collected in the epipelagic zone (Nielsen et al. 1999) but bythitids are believed to have relatively low fecundity rates (presumably as only small numbers of embryos have been found in gravid females). Reef-dwelling species, as far as is known, have only small ranges, and many may be endangered by habitat degradation.

REFERENCES

Nielsen, J. G., D. M. Cohen, D. F. Markle & C. R. Robins. 1999. FAO species catalogue. Volume 18. Ophidiiform fishes of the world. An annotated and illustrated catalogue of pearl-fishes, cusk-eels, brotulas and other ophidiiform fishes known to date. FAO Fisheries Synopsis 125 (18): I–XI + 1–178.

Schwarzhans, W., & P. R. Møller. 2007. Review of the Dinematichthyini (Teleostei: Bythitidae) of the Indo-west Pacific. Part III. Beaglichthys, Brosmolus, Monothrix and eight new genera with description of 20 new species. The Beagle, Records of the Museums and Art Galleries of the Northern Territory 23: 29-110.