ARS | Publication request: Evaluation of commercial marine fish feeds for production of juvenile cobia in recirculating aquaculture systems

Submitted to: North American Journal of Aquaculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 9, 2012
Publication Date: February 28, 2013
Citation: Wills, P.S., Weirich, C.R., Baptiste, R.M., Riche, M.A. 2013. Evaluation of commercial marine fish feeds for production of juvenile cobia in recirculating aquaculture systems. North American Journal of Aquaculture. 75:178-185.

Interpretive Summary: Commercial cultivation of cobia is gaining considerable interest in the U.S. Juveniles for stocking grow-out operations are easily produced and the fish can grow to over 10 pounds in one year. Although dietary evaluations are ongoing, knowledge regarding optimal cobia nutrition is limited. Until information is established to formulate optimal diets for cobia, it is important to identify suitable commercially available feeds for profitable production. Therefore, the present study was conducted to evaluate three commercially available marine fish diets for their effect on production characteristics and efficiency in cobia. Faster growth, better feed conversion, and better retention of dietary protein was observed in the rank order Diet A > Diet B > Diet C, although total nutrient composition was similar. The results suggest the differences were due to the quality of proteins used. Feed is one of the highest costs of fish production with protein accounting for more than 50% of the cost. In the current study, cost of the feed per Kg of fish produced was US $1.55, $1.43, and $2.30 for diets A, B, and C, respectively. In formulating feeds on a least-cost basis, where lower cost ingredients are substituted on an equal nutrient basis, it is essential to ensure cobia diets contain high quality proteins to maximize profits.

Technical Abstract: The effect of feeding three commercially available diets manufactured by three U.S. feed companies on production characteristics and body composition of juvenile cobia Rachycentron canadum reared in recirculating aquaculture systems (RAS) was evaluated in a 57 d growth trial. Juvenile cobia (26.7 +/- 0.9 g, mean weight +/- SE) were stocked into three tanks within each of four RAS at an initial density of 1.2 kg/m3. After stocking, fish were fed one of three diets for growing carnivorous marine finfish (coded Diet A, 50% crude protein (CP):15% crude lipid (CL), Diet B, 45% CP:16% CL, and Diet C, 44% CP:15 % CL), all at a targeted feed rate of 3-5% body weight per day. At two week intervals, 10% of the population of each tank was sampled to determine mean weight, weight gain, instantaneous growth rate (G), food conversion efficiency (FCE), and biomass. At termination of the trial the entire population of each tank was harvested to determine the same characteristics and survival. In addition, fish were sampled to determine relative whole body composition, energy retention, protein efficiency ratio (PER), and protein productive value (PPV). Final weight (203.3 g), G (0.036 d-1), FCE (92.2%), biomass (7.3 kg/m3), and PER (1.64) of fish fed Diet A were significantly higher than those of fish fed the other two diets. No differences in crude protein, gross energy, ash, or crude lipid content were observed among fish fed the three diets. Fish farmers must be vigilant using similar “off-the-shelf” marine fish diets from different manufacturers since performance can differ. Commercial feed manufacturers must be quick to respond and adapt new information regarding species-specific dietary requirements as well as digestibility and palatability of traditional and novel feed ingredients as capture fishery resources become more limited.