BIOLOGY:

Cobia have an elongated body with a long, depressed head and a broad snout.  The top of the body ranges in color from a dark brown to silver.  Pronounced racing-stripes run laterally along the length of the fish from snout to tail in young cobia, but become obscured in adults.  The skin is smooth with small embedded scales.  The first of two dorsal fins is composed of 7-9 short, sharp spines not connected by a membrane and each depressible into a groove.  The second dorsal fin is long, with 31 soft rays connected by a membrane and the anterior portion elevated.  Cobia have two anal spines and 24 anal soft rays.  The caudal fin is lunate in adults and more truncated in young.  The eyes of cobia are small and the lower jaw projects past the upper jaw. Cobia have bands of villiform teeth on the tongue, roof of mouth, and jaws.  Cobia do not have an air bladder. 

DISTRIBUTION:

Cobia are a migratory coastal pelagic species distributed throughout tropical, subtropical and seasonal temperate waters worldwide excluding the central and eastern Pacific Ocean.  Cobia are found in low concentrations around offshore reefs and inshore structures in bays and estuaries near the coast as well as continental shelf waters to depths of 3,900 feet (1200 m).  Cobia can often be found around oil platforms in the Gulf of Mexico.  The primary factor determining range is temperature.  Preferred water temperature is above 68 °F (20 °C) with an overall range of 60-89 °F (16 to 32 °C).     

HABITS:

Cobia are fast swimming carnivores that feed on a wide variety of fishes, cephalopods, and crustaceans, especially crab.  Cobia may travel alone, but typically hunt for food in packs of 3-100 fish or follow larger carnivores like sharks and rays to scavenge the remains. 

SPAWNING:

Cobia spawn in coastal and offshore surface waters during daylight hours between spring and summer months.  The optimal spawning temperature range is between 24 and 29 °C with an optimal salinity between 29 and 32 ppt and a slightly alkaline pH (~7.8).  Spawning adults are believed to form small groups where, following courtship behavior, females release hundreds of thousands to millions of heavily pigmented, buoyant, spherical eggs averaging 1.24mm in diameter that hatch within 24-36 hours post-fertilization depending on temperature.  Females are believed to reach sexual maturity at age 2 while males reach sexual maturity at age 1.  Spawning experiments have shown that one to two year old captive cobia display 6 weeks of courtship behavior but do not spawn without hormonal treatments. 

GROWTH:

Cobia grow very rapidly achieving marketable size of 4-6 kg within one year.  Females grow faster and larger than males.  The largest cobia landed was 6.5 feet (2 m) long and weighed 135 pounds (61 kg).  Cobia may live as long as 15 years in the wild.

USES:

In the United States, there is no commercial fishery for wild cobia, but they are a very popular sportfish in the United States coastal waters, especially during seasonal migrations.  Cobia are becoming extremely popular as a high-value food fish both domestically and abroad.    

NUTRITION:

Juvenile cobia fed pelleted diets have a minimum crude protein requirement of 40% and an optimal dietary protein requirement of 44.5% with solvent-extracted menhaden fish meal.  The minimum dietary lipid requirement of cobia is 5.76%.  Twenty percent replacement of fishmeal with soybean meal has been shown to improve growth of cobia and feed conversion rate compared to diets containing 45% crude protein with 44.8% fishmeal.  Diets containing fermented or phytase-treated soybean meal showed significant enhancement of zinc retention compared to solvent extracted soybean meal. Optimal feed conversion ratio (FCR) of adult cobia fed pelleted diets containing 42-45% protein is 1-1.8, whereas the FCR of juveniles is typically around 3.8.  Juvenile cobia can utilize dietary carbohydrates at relatively high levels for a marine carnivore.  Cobia fed diets containing 36% soluble carbohydrates in the form of dextrin and only 3% crude lipid had significantly better weight gain than cobia fed an isocaloric diet (293 kcals/ 100g dry diet) containing 0% carbohydrates and 18% crude lipid.

CULTURE:

Cobia production is a developing industry worldwide.  Cobia are typically spawned in tanks or 5-foot-deep ponds.  Larvae are then transferred to shallow nursery ponds and fed L- type rotifers (3-5 rotifers/ml) 2-8 days post-hatch (dph) followed by AF Artemia naupii 6-10 dph and enriched EG Artemia 9-30 dph.  Larval cobia are generally weaned to pelleted floating diets 20-45 dph and size-graded every 4 to 7 days to reduce cannibalism.  Two to five gram fingerlings are then transferred to larger ponds and fed to satiation several times per day.  One-ounce (~30 g) fingerlings are then transferred to larger ponds or near-shore cages and grown to approximately 2 lbs (~1 kg).  Cobia are then grown-out in net pens or open water cages.  Juvenile cobia have also been successfully grown to marketable size in recirculation raceways within 1.5 years.  Dissolved oxygen must be maintained above 5 ppt at all times to minimize stress and maximize growth.  Moderate to high salinity and temperature are required for optimal health and sustained growth. Cobia will stop feeding when water temperatures drop below 16-17 °C and median lethal temperature for juvenile cobia is 12.1 ± .36 °C.  A salinity of 5g/L has been shown to significantly reduce hematocrit and plasma osmality values.   

DISEASES:

Cobia are rather hardy as adults, but can be susceptible to parasites, bacteria, and viruses common to many warm water marine species.  Parasites that may become a problem during production are Trichodina, Myxosporideans, Neobenedenia, and Amyloodinium ocellatum.  Serious bacterial infections that affect cobia include pasteurellosis, vibrosis, and streptococcosis.  Severe viral infections may result from the iridovirus Lymphocystis. 

MARKETING AND ECONOMICS:

The firm, white flesh of cobia is very desirable to many consumers worldwide.  The extremely rapid growth rate, hardiness, high fecundity, and low feed conversion may allow the commercial production of cobia compete well with swordfish and grouper.    Cobia have been successfully cultured in Taiwan since 1994 and has become an economically important commercial species as sashimi in Japanese and effluent Chinese markets.  Taiwan is currently the largest producer of cultured cobia producing over 3,200 metric tons annually with a value of $16 million U.S.  There is tremendous potential for large-scale commercial production of cobia in the United States as new technology and culture techniques become available.  The current market value of cobia in Miami from Puerto Rico is $4.50/lb and in California from the Philippines is $3.75/lb.   

REFERENCES:

Arnold, C.R., J.B. Kaiser, and G.J. Holt. 2002.  Spawning of cobia Rachycentron canadum in captivity.  Journal of the World Aquaculture Society 33: 205-208.

Chen, H.Y. 2005.  Nutritional problems of cobia fed with feeds rich in plant ingredients. World Aquaculture. May 9-13. Bali, Indonesia. 

Chou, R.L., M.S. Su, and H.Y. Chen. 2001.  Optimal dietary protein and lipid levels for juvenile cobia Rachycentron canadum.  Aquaculture 193: 81-89.

Chou, R.L., B.Y. Her, M.S. Su, G. Huang, Y.H. Wu, and H.Y. Chen. 2004.  Substituting fish meal w/ soybean meal in diets of juvenile cobia Rachycentron canadum. Aquaculture 229: 325-333.

Denson, M.R., K.R. Stuart, T.J. Smith, C.R. Weirich, and A. Segars. 2003.  Effects of salinity on growth, survival, and selected hematological parameters of juvenile cobia Rachycentron canadum.  Journal of the World Aquaculture Society 34: 496-503.

Dodd, Q. 2001.  US cobia culture meets early success.  Hatchery International 1:14-17.

Franks, J.S., J.R. Warren, and M.V. Buchanan. 1998.  Age and growth of cobia, Rachycentron canadum, from the northeastern Gulf of Mexico.  Fishery Bulletin 97:459-471.

Faulk, C.K. and G.J. Holt. 2003.  Lipid nutrition and feeding of cobia Rachycentron canadum larvae.  Journal of the World Aquaculture Society 34: 368-378.

Froese, R. and D. Pauly, Eds.  2005. Rachycentron canadum.  FishBase. Location: (http//www.fishbase.org/Summary/SpeciesSummary.cfm?genusname=Rachycentron&speciesname=canadum).

Education: Biological Profiles-Cobia.  Florida Museum of Natural History Ichthyology Department.  Location: (www.flmnh.ufl.edu/fish/Gallery/Descript/Cobia/Cobia.html).

Hsu, C.Y., C.C. Chen, and C. Liao. 2005.  Marine cage culture of cobia in Taiwan.  World Aquaculture. May 9-13. Bali, Indonesia. 

Kaiser, J.B. and G.J. Holt. 2005.  Species profile: cobia.  Southern Regional Aquaculture Center Publication 7202.

Liao, I.C., T.S. Huang, W.S. Tsai, C.M. Hsueh, S.L. Chang, and E.M. Leano. 2004.  Cobia culture in Taiwan: current status and problems.  Aquaculture 237: 155-165.

Smith, T.I.J., A.D. Stokes, J.T. Tomasso, M.R. Densen, W.E. Jenkins, and H.L. Atwood. 2005.  Spawning and culture studies with cobia in South Carolina.  World Aquaculture. May 9-13. Bali, Indonesia.