Growth rates of cobia ( Rachycentron canadum) cultured in open ocean submerged cages in the Caribbean

Abstract

Growth rates of hatchery-reared cobia Rachycentron canadum cultured in submersible cages off Puerto Rico and the Bahamas were comprehensively studied and are presented, discussed and compared to those of other teleosts. Cobia grew to averages of 6.035 kg (specific growth rate (SGR) = 2.10%/day) in 363 days at the Puerto Rico site (PR) and 3.545 kg (SGR = 2.04%/day) in 346 days at the Bahamas site (BA). Growth in length is best expressed by the equations: y = 12 + 0.18 x; r 2 = 0.59 at PR and y = 12 + 0.16 x; r 2 = 0.86 at BA. The Laird–Gompertz model was used to represent growth in weight to best express the rate of decline in growth rate with age ( α = 0.006194 PR and α = 0.006323 BA), which occurred at the onset of precocious maturation for this species at 2.0–4.5 kg in 300 days post hatch (dph). The exponents ( b) of length–weight relationships calculated (3.31 at PR and 3.20 at BA) demonstrate that cultured cobia exhibit greater condition factors than their wild counterparts ( b = 2.8) and explain the morphological differences observed between wild and culture cobia. Final stocking densities of 5 and 15 kg/m 3 were estimated at PR and BA, respectively. Average water temperatures for the duration of the growout cycle were 27.8 °C at PR and 25.5 °C at BA. Results show that growth rates of cobia vary widely and suggest a negative effect of lower temperature and increasing stocking density. These trials also demonstrate, for the first time, that growout of cobia is technically feasible in submerged open ocean cages.