Sea cage farming of cobia
Sea cage farming of cobia
A.K. Abdul Nazar, R. Jayakumar,
G. Tamilmani and M. Sakthivel
Mandapam Regional Centre of CMFRI
Mandapam Camp - 623520, Tamil Nadu, India
175
Sea cage farming of cobia
A.K. Abdul Nazar, R. Jayakumar, G. Tamilmani and M. Sakthivel
Mandapam Regional Centre of CMFRI
Mandapam Camp - 623520, Tamil Nadu, India
Introduction important marine fishes can be cultured in any
of the four culture systems like ponds, raceways,
In recent years interest in aquaculture is gain-
recirculation systems or cages. In the simplest
ing greater momentum. The breeding and rear-
term, a cage is an enclosure in the water body
ing of aquatic plants and animals in enclosures/
whereby the juveniles of aquatic animals are kept,
confinements, has increased mainly due to over
fed and grown to a marketable size. Cage culture
exploitation of aquatic resources and declining of
uses existing water resources (ponds, rivers, es-
fish catches in major traditional fishing grounds at
tuaries, open ocean, etc.) but confines the fish
a global level. The farming of fish is widely rec-
inside some type of mesh enclosure. The mesh
ognized as the best alternative to meet the protein
retains the fish, making it easier to feed, observe
requirements of the expanding population and
and harvest them. The mesh also allows the water
to provide them with alternative livelihood op-
to pass freely be¬tween the fish and surround-
portunities for their socio-economic upliftment.
ing water resource, thus maintaining good water
In many countries, especially in the developing
quality by removing wastes. In recent years, cage
world, fish and other aquaculture products serve
culture has emerged as the most viable method of
as the main source of cheap protein to combat
sea farming.
malnutrition and under-nutrition. Fish are having
essential amino acids that are often lacking in ce- Cage culture probably originated with fish-
real protein substitutes. Value-wise, cultured fish ermen who used cages to accumu¬late fish for
products compete with poultry and livestock in market. Over time, they learned to feed the fish in
the local market. Nutrition - wise, however, aqua- these cages to increase their size and improve their
culture products are more efficient in converting overall health. The first cages used for just holding
food into body tissue than poultry or livestock. fish were probably developed in Southeast Asia
Aquaculture is the fastest growing animal food at the end of the 18th century. These cages were
producing sector in the world. It has delivered constructed of wood or bamboo and the confined
growth in production volumes of almost 8% per fish were fed trash fish and food scraps. Modern
annum over the past 50 years, approximately cage culture in the U.S. began in the 1950s with
twice the rate of global GDP growth during this the advent of synthetic materials suitable for cage
period. From output of less 1 million tonne per construction. There has been little research on ma-
year in the 1950’s, aquaculture now produces al- rine cage systems because of regulatory issues, a
most 100 million tonnes per year. Globally, fish limited number of good quality sites and high cost
today provides more than 1.5 billion people with of research. In freshwater sector, cage cul¬ture
almost 20% of their average per capita intake of allows farmers to use existing water resources that
animal protein, and 3 billion people with 15% of may or may not be used for other purposes. The
such protein. The average person consumes 18 fish produced are usually sold to local niche mar-
kilograms of fish products per year. With a grow- kets. As wild-capture fisheries have declined and
ing global population and health awareness the aquaculture has ex¬panded, these niche markets
per capita consumption of fish and fisheries prod- have also grown. As a result to cater the demand
ucts are expected to grow further. Commercially more entrepreneurial opportunities have grown
177
CMFRI Manuel Customized training Book
for cage farming. The cage culture was initiated ing, boat¬ing, swimming, irrigation or live-
in Norway during 70s and developed into an or- stock watering.
ganised industry, particularly for salmon farming.
Cage farming requires low capital investment
Similarly the cage culture has spread in South East
and the farmer can expand production with
Asian countries for culture of a variety of fishes.
additional cages or intensify production by
The major advantage in these countries is that
they have large, calm and protected bays to ac- increasing the stocking density at an optimal
commodate the cages safely against natural bad level.
weather conditions. Species selection
Advantages of Cage Culture Cage culture in open seas requires a fish va-
riety with the basic characters like, suitability for
1. Effective use of Resources
marketing, commercial importance, consumer
Cage culture can be established in any suitable accepted fish, easy to culture, adaptability to the
body of water, including open seas, backwa- cage environment, acceptance to artificial diets,
ters, lagoons or river mouths with proper water faster growth rate and resistant to common diseas-
quality, seed, feeding strategies, access and per- es. A variety of commercially important marine
mission from local authorities. This flex¬ibility fishes including, Cobia Rachycentron canadum),
makes it possible to exploit un¬derused water Seabass (Lates calcarifer), Snappers (Lutjanus
resources to produce fish. sp.), Carangids (Trachinotus sp.) and Groupers
2. Low investment (Epinephelus sp.) and lobsters are highly suitable
for cage farming. Commercial level seed produc-
The investment for pond construc¬tion and its
tion technology for majority of these fishes has
associated infrastructure (electricity, roads, wa-
been developed in many of the South East Asian
ter wells, etc.) are much higher than the cage
countries.
farming, which is practiced in an existing water
body and can be less expensive. At low den- Cobia (Rachycentron canadum)
sities (when compared to pond water spread
Cobia has gained popularity as a good candi-
area) cages placed in open seas, backwater and
date for mariculture due to its rapid growth and
lagoons do not require aeration. Cage materials
are not much ex¬pensive and can be mended white meat of versatile use. It is considered as
with little experience. one of the most promising candidates for warm-
water marine fish aquaculture in the world. Being
3. Simple farming operations the only member of the family Rachycentridae, it
In cage farming, observation of the growth is found in the warm, temperate to tropical wa-
and health status of the fish is easy and simple. ters of the West and East Atlantic, throughout the
The observation of fish behaviour, espe¬cially Caribbean and in the Indo-Pacific off India, Aus-
feeding behaviour, is critical in avoiding prob- tralia and Japan. To date, research and develop-
lems related to stress and disease outbreak. ment of cobia aquaculture has been initiated in
over 23 countries and territories, half of them in
4. Easy harvesting methods
the Asian-Pacific region. Global aquaculture pro-
Cages are usually harvested by mov¬ing them duction of cobia has been increased rapidly from
into shallow water, crowd¬ing the fish into a only 9 tonnes in 1997 to nearly 30,000 tonnes
corner of the net. Otherwise, the cage net can in 2007. Statistics of FAO (2009) show that the
be lifted par¬tially out of the water so that the Since late 1990, cobia aquaculture production
fish are crowded into a smaller volume, and has been steadily expanding in Asia, primarily
then it can be harvested. This makes it possible in Taiwan, Vietnam and China, but also in other
to partially harvest fish from cages as and when Southeast and Indo-Pacific Asian countries includ-
needed for local markets. ing the Philippines, Indonesia, Iran and Reunion
5. Multi-use of water resources Island. Although cobia production is expanding
rapidly, combined production of Asian countries
The confinement of fish in cages will not affect is still rather lower.
other uses of the water resource, such as fish-
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Sea cage farming of cobia
Cobia farming techniques developed by CMFRI The fingerlings from nursery phase 1 have to
be transferred to these floating nursery sea cages.
India is late starter in cobia research and the
The stocking density biomass at this phase can be
seed production of cobia was achieved for first
maintained at 1.8-3.0 kg/m3. The fingerlings have
time in India by the Mandapam Regional Cen-
to be fed @ 5% total biomass of fish with chopped
tre of Central Marine Fisheries Research Institute
low-value fishes (Sardine, lesser sardine, rainbow
(CMFRI). Later the farming protocols in the High
sardine, etc.) twice daily. Net cages have to be
Density Polyethylene (HDPE) cages and Galva-
changed based on the subjective assessment of
nized Iron (GI) cages with different feeding strate-
clogging of the net in order to have sufficient wa-
gies were developed, tested and validated. Out of
ter exchange. Random sampling has to be carried
this farming trials an economically viable farming
out weekly with the sample size of 30 nos. per
methods has been evolved. These farming meth-
cage. This phase can be continued for about 4
ods have been executed in a participatory farm-
weeks.
ing demonstration with M/s. Vitality Aquaculture
Pvt. Ltd., Tuticorin and successful harvest of co- Grow-out phase
bia was made during May 2013 in the presence
The grow-out culture has to be carried out in
of the Director General, ICAR, New Delhi. The
circular floating sea cages of 6 meter diameter.
basic protocols followed for cage culture of cobia
The cage frames should be made up of HDPE
in different phases are narrated as below:-
pipes or GI pipes. The handrail has to be fixed
Nursery Phase 1 at half meter height form the base. The space
between inner and outer rings of the cage has to
The 4 weeks old fingerlings were reared for
be kept as one meter. The net cages fabricated
6 weeks indoor (Nursery Phase 1) followed by 8
with HDPE ropes of 2.5 mm thickness and the
weeks outdoor (Nursery Phase 2) before stocking
mesh size of 40 mm for inner net cage and 60 mm
in grow-out cages. The nursery phase 1 can be
for outer net cage has to be used. The depth of
carried out in FRP tanks of 7 ton capacity with 5
the net cages should be maintained at 4.0 meters
ton filtered sea water. The stocking density has to
from the base. The shape of the net cages can
be kept as 8 nos. per litre. The fingerlings have to
be maintained with circular ballast. The cages
be fed with INVE (Thailand) formulated diet (as-
were floated and moored as mentioned in Nurs-
sorted size from 400 µ to 1200 µ) thrice daily.
ery Phase 2. The juveniles from nursery phase
The weaning to chopped low-value fishes can be
2 have to be transferred to these grow-out sea
practised during the last week of this phase. The
cages. The stocking density at this phase has to
water exchange has to be done 100% daily.
be maintained at 3.0-5.0 kg/m3 or 750 nos of ju-
Nursery Phase 2 venile cobia per cage. The juveniles can be fed @
The nursery phase 2 has to be carried out 5% total biomass of fish with chopped low-value
in specially designed sea cages. These nursery fishes (sardine, lesser sardine, rainbow sardine,
cages should be made of HDPE pipes or GI Pipe etc.) once daily. Net cages have to be changed
(C - Class type) material. The dimension of the based on the subjective assessment of fouling of
square sea cage has to be kept as 4x4 meter with the net in order to have sufficient water exchange.
the handrail fixed at one meter height from the Random sampling has to be carried out at month-
base otherwise a circular cage of 6 meter dia can ly intervals with the sample size of 30 nos. per
be used. The net cages fabricated with HDPE cage. The entire grow-out culture can be carried
ropes of 2.5 mm thickness and the mesh size has out for a period of 6- 7 months.
to be used are 20 mm for inner net cage and 40 Performance
mm for outer net cage. The depth of the net cage
shall be kept 3 meters from the base. The shape The fingerlings stocked in indoor nursery at
of the net cages has to be maintained with ballast. around 2 grams and will attain an average weight
The buoyancy of the cages can be enabled by ty- of 45 grams in 6 weeks, followed and about 70
ing HDPE drums with the cage frame and has to grams in another 4 weeks of outdoor nursery
be moored with two numbers of Galvanized Iron rearing. The juveniles would reach an average
(GI) anchors of 70/100 kg each in opposite direc- weight of 1.0 kg in 4 months and 2.5 – 3.0 kg in
tions. 6- 7 months of grow-out culture in sea cages. The
179
CMFRI Manuel Customized training Book
grow-out fishes would reach an average weight of 7.0 kg with a maximum weight of 8.0 kg within the
culture period of one year which is almost 100 times the growth of the initial weight.
The unit cost estimate, performance of production and economics of operation gained through the
farming trials and participatory demonstration were worked out and given below:-
Unit cost economics for cage farming of cobia (in a 6 m diameter GI cage)
Sl. No Head of expense Cost in Rs.
Capital Expenditure
Cage and Net
1 Cage ( 6 meter dia) made of ‘C‘ class GI Pipe of 1.5 inch dia) 50,000.00
2 Mooring 15,000.00
3 Nets ( 2 Inner net and one outer net with ballast pipe) 60,000.00
Sub Total 1,25,000.00
Operational Expenditure*
1 Cost of 750 Numbers of cobia seeds @ Rs 10/seed 7,500.00
2 Transportation 5,000.00
3 Cost of 12.82 tonnes of low value fishes @ Rs.25,000/tonne 3,20,500.00
4 Labour Charges @ Rs.1000/ Person for 7 months for 2 persons 14,000.00
5 Boat Hire & Fuel Charges 10,000.00
6 Harvesting Charges 5,000.00
7 Miscellaneous Expenses 10,000.00
Sub Total 3,72,000.00
Grand Total of Capital & Operational expenditure 4,97,000.00
*Item No. 4 &5 worked out based on the average expenditure/month for a cluster of 10 cages
Sl. No Production Estimates
1 Survival 95% = 712 fishes
2 Feed Conversion Ratio = 1 : 6
3 Average size of each fish at the time of harvest =3kg
4 Total harvest = 2.136 tonnes/cage
5 Sale price of the produce @ Rs.280/kg = Rs. 5,98,080/-
Gross Income from the harvest = Rs. 5,98,080/-
Sl. No Economics
1 Gross income from Harves - Rs. 5,98,080/-
2 Operational expenditure - Rs. 3,72,000/-
3 Gross income – Operational expenses - Rs. 2,26,080/-
Net Profit = Rs. 2,26,080/-
4 Partial repayment of the capital expenditure - Rs. 25,000/year
(Capital cost Rs. 1,25,000 – Subsidy Rs. 50,000 - Rs. 75,000)
Repayment of capital @ Rs. 25,000/year x 3 years
5 Interest in the total project cost @ 11% - Rs. 52,800/-
6 Part of Capital + interest = Rs. 25,000 + 52,800 - Rs. 77,800/-
7 Rs. 2,26,080 – 77,800 = 1,48,280/-
Net profit (after repayment of interest &
part of capital expenditure) Rs. 1,48,280/-
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Sea cage farming of cobia
Unit cost economics for a cluster of 10 cages to take up farming of cobia
Sl.No Head of expense Cost in Rs.
Capital Expenditure
Cage and Net
1 Cost of 10 Cages ( 6 meter dia) made of ‘C‘ class GI Pipe of 1.5 inch dia) 5,00,000.00
2 Mooring materials for 10 cages 1,50,000.00
3 Nets ( 2 Inner net and one outer net with ballast pipe) for 10 cages 6,00,000.00
Sub Total 12,50,000.00
Operational Expenditure*
1 Cost of 7,500 Numbers of cobia seeds @ Rs 10/seed 75,000.00
2 Transportation 50,000.00
3 Cost of 128.250 tonnes of low value fishes @ Rs.25,000/tonne 32,06,250.00
4 Labour Charges @ Rs.10,000/ Person/month for 2 Persons X 7 months 1,40,000.00
5 Boat Hire & Fuel Charges 1,00,000.00
6 Harvesting Charges 50,000.00
7 Miscellaneous Expenses 1,00,000.00
Sub Total 37,21,250.00
Grand Total of Capital & Operational expenditure 49,71,250.00
Sl. No Production Estimates
1 Survival 95% = 7125 fishes
2 Feed Conversion Ratio = 1 : 6
3 Average size of each fish at the time of harvest =3kg
4 Total harvest = 21.375 tonnes/cage
5 Sale price of the produce @ Rs.280/kg = Rs. 59,85,000/-
Gross Income from the harvest = Rs. 59,85,000/-
Sl. No Economics
1 Gross income from Harvest = Rs. 59,85,000/-
2 Operational expenditure = Rs. 37,21,250/-
3 Gross income – Operational expenses = Rs. 22,63,750/-
Net Profit = Rs. 22,63,750/-
4 Partial repayment of the capital expenditure = Rs. 25,000/year/cage
(Capital cost Rs. 12, 50,000 – Subsidy Rs. 5,00,000 = Rs. 7,50,000)
Repayment of capital @ Rs. 2,50,000/year x 3 years
5 Interest in the total project cost @ 11% = Rs. 5,46,838/-
6 Part of Capital + interest = Rs. 2,50,000 + 5,46,838 = Rs. 7,96,838/-
7 Rs. 22,63,750 – 7,96,838 = 14,66,912/-
Net profit (after repayment of interest &
part of capital expenditure) = Rs. 14,66,912/-
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CMFRI Manuel Customized training Book
HDPE Cage (6 meter Dia) GI Pipe Cage (6 meter Dia)
Cobia fingerlings (50 days old) Cobia juveniles (While feeding)
Cobia Juveniles (3 kg size) Harvested Cobia
182
