Colossal Armored Suckermouth Catfishes!

I apologize to those who saw an accidentally published early draft of this post. Anyways:

Pseudacanthicus histrix reportedly measuring 0.91 m (total length?). Contra to the prior reference, this is not Acanthicus hystrix. Source unknown.

At some point in my childhood, I was awestruck by several very large loricariids at the Shedd Aquarium. I had a ~30 cm (TL) Hypostomus plecostomus at home, among the biggest I had seen up until then, but the largest individuals from those two species at least doubled that. Does anybody know if the fish are still there - and what species they are? The concept of colossal loricariids has been bumping around in my brain ever since...

As you probably noticed, in a couple recent posts I discussed how invasive armored suckermouth catfishes (Loricariidae) impact local ecologies. Several of the Pterygoplichthys species appear to be the cause of the most problematic "infestations"; their large body size is probably one of the traits responsible for their success, as it allows them to outcompete indigenous species and escape predation. Exactly how large these and other loricariids can grow is an interesting question, to me at least, hence this post.

Determining the sizes of loricariid species is a needlessly complicated affair - weight data is sparse, maximum lengths are given more frequently than averages, total length (TL - counting the caudal fin) is sometimes used instead of standard length (SL), confusion between cm and mm sometimes occurs, species are often confused, and there are wild rumors. The definition of a "colossal" loricariid should be something like 10+ kg on average, but given the current state of the data I'll consider any species which can exceed 50 cm SL "colossal".


The Colossi That Never Were

Attention researchers: If you see a loricariid listed at ~100 cm, please check to see if the original source is actually in mm!

Fishbase listed Peckoltia braueri at 88.6 cm maximum SL, which would make it larger than almost every other loricariid. A photograph from Fishbase gives the impression of a much smaller animal, and I subsequently noticed that while one other site gave a similar size, several others did not. I do not have access to the original description nor the paper that Fishbase cited, but I found that Armbruster and Werneke (2005) noted that the largest species of Peckoltia had a SL of 103 cm. My hunch turned out to be correct and the issue is currently being fixed.

Fishbase lists Lasiancistrus guacharote at an incredible 135 cm TL... and stated that it occurs in Puerto Rico. In the last post the notion that Puerto Rico had any native loricariids was discounted and consultation of the same source revealed that the L. guacharote was 119.5 mm SL (Armbruster 2005). It is possible that both records are in fact from the same specimen. Unfortunately, at least one source currently reports the erroneous locality and size.

While this erroneous information probably hasn't become too entrenched, I think it is still worth pointing out the errors and their likely cause.


Rumors of Mega-Colossi, Conflicting Math, and Pterygoplichthys

The blog NO FORM - NO SUBSTANCE reported a rather lively radio broadcast from the Philippines which claimed that invasive "janitor fish" (Pterygoplichthys disjunctivus) reached 2-3 meters and 30 kilograms! One telltale factor of a "fish story" is an implausible length-weight relationship, which was my first impression with the rumor.

The quickest way of roughly extrapolating mass (assuming isometric growth) is the square-cube law; if we use the 0.512 m/1.8 kg P. multiradiatus (?) from my last post as a template, this means that a 2 m P. disjunctivus would be 3.9 times longer and implies that it is (3.9³ =) 60 times more massive, which is over 100 kg. Liang et al. (2005) recorded the lengths and weights of over 500 invasive P. multiradiatus in Taiwan and extrapolating from their averages predicts about 2 kg for a 0.512 m specimen, suggesting that isometric growth is likely and that the 100+ kg prediction is not off the mark. But...

Growth is not necessarily isometric (i.e. proportions vary) so the equation W = aL^b is used, where L = total length (cm), W = weight (grams), b = exponent describing growth, a = a constant, for those interested, there's this. Using the equation from Liang et al. (2005) predicts 22-27 kg (depending on gender) for a 2 m (standard length) P. multiradiatus and Shukor et al. (2008) predicts 27.6 kg for a similarly sized P.  pardalis. Since laypeople generally use total length (including the caudal fin) when measuring fish and scientists use standard length (distance to caudal peduncle) this suggests that 30 kg is probably still too light for a 2 m Pterygoplichthys - but it is still probably close. To put that in perspective, a 2 m sturgeon weighs around 60 kg and a 1.8 m eel is over 20 kg - in other words the weight derived from W = aL^b is clearly off the mark. I'm assuming that while it is valuable as a tool for determining traits like condition, it has limited ability to predict length-weight relationships considerably outside the range of data used to calculate it. Or I could have screwed everything up somehow...

So how large can Pterygoplichthys species get? Fishbase lists the maximum size of P. pardalis at 42.3 cm SL; however Shukor et al. (2008) report that invasive individuals from the Malaysian peninsula are in their best condition between 30 and 40 cm and according to their Figure 1, 5 individuals out of 928 were ~50 cm in length. Invasive P. multiradiatus in Taiwan averaged about 30 cm for 537 specimens with a maximum length of 43.7 cm SL (Liang et al. 2005); Fishbase lists a cool 50 cm TL for the maximum, possibly equivalent to the SL. However, Bunkley-Williams et al. (1994) list a possible 51.2 cm specimen and cite Page and Burr 1991, which give 70 cm. Pterygoplichthys undecimalis reportedly gets up to 50 cm SL, but I cannot find (or read the language of) any corroborating sources. Quevedo and Reis (2002 - citing Schaefer 1986) state that Pterygoplichthys can reach one meter in length. Not knowing the species or any other details is certainly frustrating.


Other Colossal Loricariids

The same source states that Panaque and Acanthicus also can exceed 1 meter in length. According to Fishbase, P. nigrolineatus is the largest species at 43 cm TL - leaving me perplexed. The Acanthicus species are much more likely to reach 1 m; Fishbase and its source list A. hystrix at SL, this source from 1890 lists the length at 0.71 m, this aquarium atlas lists the length at 1.1 m, and this book lists the length at "over" 1.2 m. The Fishing World Records page also lists 1.2 m, although it does not lists sources and confuses Pseudacanthicus histrix for A. hystrix. That website and Planet Catfish also list A. adonis at 1 meter, strangely Fishbase puts it at a mere 20.6 cm SL.

As far as I can tell, Pseudacanthicus histrix is the largest loricariid for which there is reasonable evidence. The lack of peer-reviewed literature on the species, and the paucity of data on colossal loricariids in general, is a concern. It does not seem unreasonable to assume that some loricariids can reach about a meter and 20 kg in weight, although if the individuals belong to any of the species here or even some taxa yet to be described has yet to be seen.

References:

Armbruster, Jonathan W., and Werneke, David C. (2005) Peckoltia cavatica, a new loricariid catfish from Guyana and a redescription of P. braueri (Eigenmann 1912) (Siluriformes). Zootaxa 882, 1–14. Available.

Armbruster, Jonathan W. (2005). The loricariid catfish genus Lasiancistrus (Siluriformes) with descriptions of two new species. Neotropical Ichthyology 3(4), 549-569. Available.

Bunkley-Williams, Lucy, et al. (1994). The South American Sailfin Armored Catfish, Liposarcus multiradiatus (Hancock), a New Exotic Established in Puerto Rican Fresh Waters. Caribbean Journal of Science 30(1-2), 90-94. Available.

Liang, Shih-Hsiung, et al. (2005). Size Structure, Reproductive Phenology, and Sex Ratio of an Exotic Armored Catfish (Liposarcus multiradiatus) in the Kaoping River of Southern Taiwan. Zoological Studies 44(2), 252-259. Available.

Quevedo, Rodrigo and Reis, Roberto E. (2002). Pogonopoma obscurum: A New Species of Loricariid Catfish (Siluriformes: Loricariidae) from Southern Brazil, with Comments on the Genus Pogonopoma. Copeia 2002, 402-410.

Shukor, Samat A., et al. (2008). Length-weight Relationship and Condition Factor of Pterygoplichthys pardalis (Pisces: Loricariidae) in Malaysia Peninsula. Research Journal of Fisheries and Hydrobiology, 3(2), 48-53. Available.

Invasion of the Armored Suckermouths!

Alternate title: Endangered pelicans try to swallow invasive catfish. Pelicans suffocate. Die.

Due to the probability of a cease-and-desist letter from England, I'll weave the hinted-at tale above into the tapestry of woe that the armored suckermouth catfishes have caused.

My highly derivative alternate title refers to a phenomenon that occurred in Oct. 1992* in the lower Loiza and Gurabo Rivers of Puerto Rico: at least twenty Brown Pelicans (Pelecanus occidentalis, a locally endangered species at the time) were found strangled to death with large armored suckermouth catfish (over 40 cm, 16" in length) lodged in their throats (Bunkley-Williams et al. 1994). It is worth pointing out that Brown Pelicans typically take prey under 25 cm in length (ref.), do not have bills over 16"/40 cm in length (according to this), and weigh 2-5 kg compared to the ~1 kg that the catfish weighed**. The possibility that Brown Pelicans can successfully swallow prey of that size cannot be precluded, so the extensive armor and unusual morphology*** of the catfish may have been the fatal factors. As to why the phenomenon was so widespread, the catfish became established in Puerto Rico only a few years before and their ease of capture may have prompted curiosity towards a new potential food source. No more reports have been published, so it is possible that the local Brown Pelican population has learned to avoid the catfish, which are probably now permanently established. And sorry to those seeking out morbid photos of the failed loricariid consumption, photographs do not seem to have been published, or even taken as far as I know.

* The table actually says "Ott 1992", I'm fairly certain it's a typo and not some hyper-obscure Latin abbreviation.

** The first recorded loricariid from Puerto Rico was a 1.8 kg, 51.2 cm "Hypostomus plecostomus" - this identification is dubious and the (lost) specimen was presumably the same species as the ones the pelicans swallowed (Bunkley-Williams et al. 1994). Anyways, extrapolating from that record gives 0.86 kg for a 40 cm specimen - I stated ~1 kg due to uncertainty and the implication that 40 cm was a minimum. 
*** Hoover et al. (2004) suggest that the dorsal and pectoral defensive spines were the cause of the mortalities.

Bunkley-Williams et al. (1994) identified the invasive loricariid catfish species as Liposarcus multiradiatus, which is now (again, actually) known as Pterygoplichthys multiradiatus. Puerto Rico has no native loricariids* and while a report occurred as early as 1983 (a likely accidental), P. multiradiatus became established in eight rivers and two reservoirs in the early 1990's, with numbers significant enough to support a local fishery in one area (Bunkley-Williams et al. 1994). While there are markets for the fish in the food and pet industries (at least one fish farm existed on the island for the latter purpose), Bunkley-Williams et al. (1994) suggested that the unexpectedly large size reached by the species led to amateur aquarists discarding them. The catfish appear to be incredibly tolerant of handling stress and can even reportedly survive out of the water for hours** (Bunkley-Williams et al. 1994).


* The type locality of Lasiancistrus guacharote (formerly Hypostomus) was Puerto Rico, but it turns out that this is in error, the species is actually from Venezuela and Columbia (Armbruster 2005). 
** Over 30 hours, in fact (Armbruster 1998 citing Val and De Almeida-Val 1995). They accomplish this by breathing air into an enlarged and highly vascularized stomach, which primarily functions to survive low-oxygen conditions in water (Armbruster 1998). Hoover et al. (2004) documented Pterygoplichthys specimens which apparently entered a period of estivation in burrows, from which they recovered as soon as they returned to water. The implication is that they can survive considerably longer than 30 hours out of the water. Oh, and they can also move on land during extreme environmental conditions.


If the trouble caused by Pterygoplichthys multiradiatus seems familiar, that's because a couple posts ago I discussed how P. disjunctivus (and/or hybrid descendants) specimens in Florida grazed on manatees to a likely deleterious effect. I didn't properly introduce the loricariid catfishes then, and I'm not sure how I passed on such a succulent tangent. So here's a scenic detour through the world of these bizarre armored suckermouth catfishes.

P. multiradiatus from the Wikipedia Commons.

Ideally, the common name "armored suckermouth catfishes" should be used for Loricariidae since they are not the only clade with extensive armor (Callichthyidae) nor are they the only ones with a sucker mouth (Astroblepidae). Loricariidae and Astroblepidae are sister clades (indicating the suckermouth is a shared derived character) and Callichthyidae is a more distant relative (indicating the extensive armor is convergent, unless lost numerous times) in the greater clade Loricarioidea, which includes everything from parasites to a monotypic oddity. Loricariidae itself has a staggering array of morphological variability: Panaque nigrolineatus (Ancistrinae) has an incredibly large head, Tim Burton-esque stripes, and the ability to digest wood with the aid of bacteria; some species (e.g. Farlowella amazonum - Loricariinae) have a body shape reminiscent of pipefish (likely for similar camouflage needs); the Sturisoma species and relatives (Loricariinae as well) look similar except with very exaggerated fins; dwarf suckermouths (Otocinclus et al. - Hypoptopomatinae) look more like generic tetra-like fishes than highly derived catfishes at first glance; one Ancistrus species is a blind cave-dweller, others have bizarre facial tentacles (Ancistrinae); Chaetostoma sovichthys (Ancistrinae) and relatives hardly look like fish at all in dorsal view - more like a revisitation of Cephalaspis or even the ichthyological answer to Triops. The point is, with 700+ species, Loricariidae is a very successful clade - considering they're mostly freshwater* and restricted to one continent. Adriaens et al. (2009) discussed the highly derived jaw morphology** which apparently allowed the loricariids to radiate into the algae-scraped niche; exactly how the numerous species differ niche-wise has not had much discussion.The species Adriaens et al. (2009) used as a model for their study of loricariid jaw mechanics? - Pterygoplichthys disjunctivus.

* Although sources like Fishbase state that they are strictly freshwater, Hoover et al. (2004) report that they occur in brackish water. 
** Catfish jaw morphology is normally conservative, but loricariid jaws have a uniquely mobile upper jaw (as in, it typically doesn't move at all in other catfishes) and the bones of the lower jaw are decoupled to allow for asymmetric scraping movement. 


Back to the invasive loricariids. As it appears that the most widespread and damaging taxa are a few related Pterygoplichthys species (e.g. within the genus), I'll be focusing on those sailfin catfishes - distinguishable by their large dorsal fins consisting of more than 10 rays. In addition to Puerto Rico and Florida, Hawaii has a particularly noteworthy population of Pterygoplichthys and several other genera of loricariids (Bunkley-Williams et al. 1994 - citing various). In the Philippines, P. disjunctivus and P. pardalis were present in the Laguna Lake region since the 1950's and in the early 2000's were found in the Agusan marsh, one of the largest in Asia (Hubilla et al. 2007). Members of Pterygoplichthys are also established in Taiwan, Singapore, Malaysia, Indonesia, and Mexico (Page and Robins 2006, Armando et al. 2007). While Pterygoplichthys spp. are reported from a few states in the mainland USA, there is a chance that like could go from localized to very widespread and wreak havoc (Hoover et al. 2004). So what makes these loricariids particularly damaging invasive species?

The Pterygoplichthys species are capable of far more severe impacts than choking pelicans and cleaning manatees. In fact, Hoover (2004) states that the variety and severity of the ecological impacts from the catfish are unprecedented. I can't emphasize that enough. Loricariids burrow into the banks of streams and lakes in order to spawn and take refuge from droughts and cold temperatures; this behavior can erode away 4 meters of bank annually and cause increased silt loads and turbidity (Hoover et al. 2004, Hubilla et al. 2007). The increased turbidity slows down photosynthesis and likely has negative effects on the food web and energy flow (Hubilla et al. 2007). The catfishes also plow into the substrate and uproot plants, which likely reduces the abundance of native plants and may even aid in the spread of invasive plants (Hoover 2004). Invasive Pterygoplichthys, being large and bewilderingly resilient species, likely outcompete the native algae consumers, aggressively drive them away, and consume the eggs of those species and others (Hoover 2004). The presence of a ravenous algae grazer may also reduce cover for aquatic insects and disrupt the food chain by prematurely diverting nutrients into feces Hoover 2004). Having owned Hypostomus plecostomus specimens in my life, I can't help but wonder if the prodigious amount of feces that loricariids produce has some sort of impact as well.

So what can be done to prevent the potential ravaging of aquatic freshwater ecosystems by invasive loricariids? Bunkley-Williams (1994) discussed the possibility of large predatory fish controlling Pterygoplichthys numbers (Peacock bass, Cichla ocellaris, and Largemouth bass, Micropterus salmoides), however they concluded that there was no known effective predator, disease, or parasite. The Philippines populations also do not appear to have any significant predation, even from native fishermen gillnets as they are damaged from the large fish (Hubilla et al. 2007). Hoover et al. (2004) and Hubilla (2007) suggest that fisheries, possibly with government incentive, could be a way of controlling populations (presumably with better equipment) as the fish are valued for their flesh and eggs. Hoover et al. (2004) also suggested protecting banks from burrowing and isolating the "infected" areas as method for preventing the problem from becoming very widespread. Hoover et al. (2004) and Bunkley-Williams et al. (1994) suggest public education to the prevent further release of loricariids and the latter publication proposed a program to return unwanted fish from amateur aquariums. Those two papers and Hubilla (2007) all suggest that environmental laws should be strengthened in order to prevent multiple Pterygoplichthys species or even multiple loricariid genera from being established. Bunkley-Williams (1994) doubt that the invasive species can ever be eradicated, but the chances of controlling the spread of the catfishes are still good if people recognize the problem before it gets completely out of control.

I'll admit that when I was a kid I released a large loricariid into a quarry before I moved. Even though it had no chances of becoming widespread, it was still a very dumb decision. So please, if you own these catfishes, whatever you do, don't release them into the wild!

References:

Adriaens, Dominique, et al. (2009). Extensive Jaw Mobility in Suckermouth Armored Catfishes (Loricariidae): A Morphological and Kinematic Analysis of Substrate Scraping Mode of Feeding. Journal of Experimental Biology 212, 116-125. Available.

Armando, T. et al. (2007). Amazon Sailfin Catfish Pterygoplichthys pardalis (Castelnau, 1855) (Loricariidae), another exotic species established in Southeastern Mexico. The Southwestern Naturalist 52(1), 141-144.

Armbruster, Jonathan W. (2005). The loricariid catfish genus Lasiancistrus (Siluriformes) with descriptions of two new species. Neotropical Ichthyology 3(4), 549-569. Available.

Armbruster, Jonathan W. (1998). Modifications of the Digestive Tract for Holding Air in Loricariid and Scoloplacid Catfishes. Copeia 1998(3), 663-675. Available.

Bunkley-Williams, Lucy, et al. (1994). The South American Sailfin Armored Catfish, Liposarcus multiradiatus (Hancock), a New Exotic Established in Puerto Rican Fresh Waters. Caribbean Journal of Science 30(1-2), 90-94. Available.

Hoover, Jan Jeffrey, et al. (2004). Suckermouth Catfishes: Threats to Aquatic Ecosystems of the United States? ANSRP Bulletin 04(1). Available.

Hubilla, Marianne, et al. (2007). Janitor Fishes Pterygoplichthys disjunctivus in the Agusan Marsh: a Thread to Freshwater Biodiversity. Journal of Environmental Science and Management 10(1), 10-21. Available.

Page, Lawrence W. and Robins, Robert H. (2006). Identification of Sailfin Catfishes (Teleostei: Loricariidae) in Southeastern Asia. The Raffles Bulletin of Zoology 54(2), 455-457. Available.

The Benefits Of Having Stuff Grow All Over You

One would think that epibiotic growth, that is, commensal organisms attached to a living surface, would be neutral at best and a hindrance to locomotion at worst* for the basibiont, the substrate organism. 'Fouling' by epibiotic growth is a virtually omnipresent pressure in aquatic environments, so basibionts variably avoid, defend against, or tolerate epibiotic growth (Wahl 1989). Since there are potential examples beyond count, given the tendencies of this blog I'll focus on some recently described examples of tolerance from big vertebrates.

* Potential disadvantages for the basibionts includes increase in weight, decrease in flexibility, increase in friction, damage from anchoring, damage due to grazers preying on epibionts, and so forth (Wahl 1989 - citing various).

The loricariid catfish Pterygoplichthys (possibly P. disjunctivus and hybrids) was accidentally introduced to Florida and has been observed interacting with manatees while both species were present near springs during the winter, avoiding unsuitably low temperatures (Nico et al. 2009). The interaction is that the catfish graze upon the grazers:

A mother and calf with 16 loricariids. Note that manatees are typically covered in epibiotic growth. The authors recorded another instance of over 40 catfish on one individual, almost obscuring it from view. Photograph by James P. Reid, taken from Nico et al. (2009).

The heavy covering of epibionts on manatees indicates tolerance and implies either a neutral impact or a beneficial one. Nico et al. (2009) speculate that while the epibiont layer probably does not provide notable protection against UV radiation (as manatee skin is very thick), it could play a role in heat absorption. Manatee behavior towards the armored catfish is contradictory; while some individuals ignore them (Fig. 1) even if as many as 40 catfish are involved, others apparently avoid congregations of catfish and others still are irritated by the fish and attempt to dislodge them (Nico et al. 2009). Since the interaction is so recent, perhaps it is possible that manatees have not learned or evolved a standardized response. Manatees generally ignore other fish including remora species that feed on their fecal matter and bluegills that apparently feed on epibionts (Williams et al. 2003, Powell 1984); however they are not tolerant of a porgy species which occasionally nips at them (Nico et al. 2009 - citing pers. com.). The grazing on manatees could be beneficial for the removal of parasites and removal of diseased and damaged tissue, although it also carries the risk of disease transmission (Nico et al. 2009). This is a surprisingly complicated situation and clearly the role of epibionts needs to be further investigated, as do the risks and benefits of allowing fish to graze. Nico et al. (2009) speculate that manatees that avoid loricariids may move to colder water, where they expend more energy than normal attempting to maintain body heat.

The interaction between cetaceans and their epibionts seems to be less obscure than the manatee situation. In dealing with Orcinus orca predation, mysticetes have adopted fight or flight countermeasures; the Balaenoptera species are fliers while the right whales (Eubalaena spp.), bowhead whale (Balaena mysticetus), humpback whale (Megaptera novaeangliae) and grey whale (Eschrichtius robustus) are fighters (Ford and Reeves 2008). Although the number of documented cases of orcas killing mysticetes are few, the rate of scarring suggests that predation attempts are significant, likely for juveniles (Ford and Reeves 2008). The ability to sprint at considerable speeds in the Balaenoptera species seems to be a direct evolutionary response to predation, but the fight species may have evolved to be slow and maneuverable primarily because of their ecological niches (Ford and Reeves 2008). Possibly mirroring the evolution of horns in some bovids, the offensive structures in right whales and humpback whales are used both for intraspecific male combat and interspecific defense and it is not clear for what purpose they originally evolved (Ford and Reeves 2008). Although right whales and humpback whale will swing or lunge with their heads, flippers and flukes are the primary means of defense for these species; gray whales roll on their backs to protect their vulnerable ventrum (Ford and Reeves 2008).

Right whales have hardened patches of skin known as callosities on the dorsal, lateral, and ventral surfaces of the head. These callosities host thousands of amphipods, epibionts with no obvious beneficial function for the whales - apparently the cornified epidermal tissue provides their ideal habitat and harboring the arthropod is a side effect for possessing the morphology. Southern right whales, however, possess barnacles which probably do have a function in making the callosities more formidable.

The Southern Right Whale has callosities with both amphipods and barnacles. From here. Has anyone every suggested that right whales may be responsible for sightings of 'marine saurians'?

Humpback whales lack callosities, but they have analogous barnacles which fulfill the same function - and provide an unambiguous example of a positive epibiotic interaction. Humpbacks can have up to 450 kg of large barnacles ( up to a 5 cm diameter) concentrated on the head, leading edge of their flippers, tips of the tail flukes, throat pleats, and near the genital slit (Ford and Reeves 2008 - citing Clark 1966, Slijper 1962). While intraspecific purposes are also likely, it is probably no coincidence that humpback whales defend against orcas using their head, flippers, and flukes (Ford and Reeves 2008). It seems like the throat and genital regions would be particularly susceptible to either biting or ramming attacks, further suggesting the defensive function of the barnacles.

Grey whales have often continuous encrustations of barnacles on the dorsal portions of their rostrum, anterior portion of their backs as well as their flippers, fluke, and elsewhere (Ford and Reeves citing Rice and Wolman 1971). Considering the defensive behavior of the whales, once again it appears that the barnacle placement is no coincidence. Exactly how these whales attract barnacles to particular portions of their body certainly is a good question; how do the callosities of some right whales have barnacles and others don't?

Epibiosis certainly doesn't end with heat balance (maybe) and creating weapons, Wahl (1989) notes that other potential benefits for the basibiont include a supply of vitamins and/or nitrogen compounds, water retention during low tide, camouflage, mask chemical cues, and drag reduction (!) - thanks to hydrophobic bacteria on skin. There are of course many, many potential disadvantages as well.

References:

Ford, John K. B.; Reeves, Randall R. 2008. Fight or flight: antipredator strategies of baleen whales. Mammal Rev. 38(1), 50–86.

Nico, Leo G; Loftus, William F.; Reid, James P. 2009. Interactions between non-native armored suckermouth catfish (Loricariidae: Pterygoplichthys) and native Florida manatee (Trichechus manatus latirostris) in artesian springs. Aquatic Invasions 4(3), 511-519. Available.

Powell, J. A. 1984. Observations of cleaning behavior in the bluegill (Lepomis macrochirus), a centrarchid. Copeia 1984, 996-998.

Wahl, Martin. 1989. Marine epibiosis. I. Fouling and antifouling: some basic aspects. Mar. Ecol. Prog. Ser. 58, 175-189. Available.

Williams, E. H. Jr.; Mignucci-Giannoni, A. A.; Bunkley-Williams, L.; Bonde, R. K.; Self-Sullivan, C.; Preen, A.; Cockcroft, V. G. 2003. Echeneid-sirenian associations, withinformation on sharksucker diet. Journal of Fish Biology 63(5), 1176-1183. Available.