Submitted to: Florida Aquaculture Newsletter
Publication Type: Trade Journal
Publication Acceptance Date: 7/15/2008
Publication Date: 8/1/2008
Citation: Weirich, C.R., Wills, P.S. 2008. Production of cobia in recirculating aquaculture systems. Florida Aquaculture Newsletter. 66:3.
Technical Abstract: Interest in cobia Rachycentron canadum aquaculture in the US has increased greatly in the last decade due to their excellent consumer appeal, extremely rapid growth rates, and the observed success of rearing this species in Taiwan and other southeastern Asian countries. Because most cobia are grown using offshore net pens or cages, only limited information exists with respect to rearing this species using recirculating aquaculture systems (RAS). Through funding provided by USDA-ARS and the NOAA Aquaculture Program's National Marine Aquaculture Initiative, two rearing trials were conducted using commercial-scale RAS. Both rearing trials were conducted at the USDA-ARS Sustainable Tank Aquaculture Recirculating Research Facility at Harbor Branch Oceanographic Institute, Florida Atlantic University, using four 45-m3 RAS, each consisting of four 8-m3 (2,100 gallon) round fiberglass culture tanks. During both trials temperature and salinity were maintained between 27-29 C (81-84 F) and 25-28 ppt, respectively. In the first trial, juvenile cobia (initial weight = 29 g), were stocked into three tanks of each RAS at an initial density of 1.2 kg/m3 (324 fish). They were fed one of three commercial diets: Zeigler Marine Grower (MG), Zeigler Gold, or Zeigler Hybrid Striped Bass (HSB). Fish were fed twice daily at a targeted daily ration of 4-5% of body weight. Initial pellet size was 3 mm and was increased to 5 mm at 43 days after stocking. Results revealed that after 56 days fish fed the MG diet weighed more (average final weight = 311 g) than fish fed the GOLD and HSB diets. Feed conversion rate (FCR) of fish fed the MG diet (1.17) was also superior to FCR of fish fed the other diets. In addition, final density of cobia fed the MG diet (11.2 kg/m3) was significantly greater than that for fish fed the GOLD or HSB diets. Excellent survival (95 – 97%) was evident for fish fed each diet and there were no differences between treatments. In Trial 2, the effect of rearing density on production of sub-adult cobia of potential market size was determined. Cobia juveniles (initial weight = 322 g) were stocked into three tanks of each RAS, each at a different density: low (1.4 kg/m3, 35 fish); medium (2.8 kg/m3, 70 fish); or high (4.2 kg/m3, 106 fish). After stocking, fish were fed a commercial slow sinking pelleted diet (Cargill/Burris; 45% CP, 15% CL) twice daily at a targeted daily ration of 3 to 5% of body weight. Initial pellet size was 5 mm and was increased up to a final size of 12.5 mm as fish grew. Results indicated that at 4 months rearing density had no effect on production characteristics. Fish reared at all three densities exhibited excellent growth (average final weight = 2.1-2.2 kg), FCR (1.51-1.54), and survival (95.7-97.2%). Final biomass of low, medium, and high density treatments was 9.0, 18.1, and 27.8 kg/m3, respectively. Across treatment fillet yield was 42.1% and average total fillet weight of each harvested fish was 884 g (two 442 g or one lb fillets per fish). About 50 pounds of these fish were grilled at the Florida Aquaculture Association Taste of Aquaculture Legislative Reception in March, 2008. Results of both trials clearly indicate that cobia juveniles can be reared to stocker and sub-adult sizes in RAS with growth rates equal to or exceeding those reported for fish reared in net pens. These initial findings suggest that cobia may be an ideal marine species for RAS culture, as an entire crop of harvestable fish may be produced in as little as 5 ½ to 6 months after larvae are weaned to dry feeds. Ongoing research at our facility is focusing on determining optimal feeding strategies and evaluating increased rearing densities on production. In addition, research must be conducted on the economic feasibility of producing cobia in RAS and the market acceptability of fish reared to a harvest wei