Effects of rearing density on growth, physiological responses, and flesh quality in juvenile cobia (Rachycentron canadum)

Rearing density is recognized as a critical consideration in fish husbandry: whereas higher densities may increase productivity and reduce production costs, they also represent a potential source of chronic stress and may negatively affect growth performance and product quality. Accordingly, we investigated the effects of rearing density on growth, physiological responses, and flesh quality of cobia (Rachycentron canadum). Fish (46.32 +/- 0.22 g, mean +/- SEM) were reared for 42 days in a low salinity (17.6 g/L) recirculation system according to treatments designated as low density (5 fish/tank, 3.30 +/- 0.02 kg/m(3)), medium density (10 fish/tank, 6.67 +/- 0.03 kg/m(3)), or high density (20 fish/tank, 13.15 +/- 0.16 kg/m(3)). Weight gain and specific growth rate were significantly higher among fish reared at low density; however, feed intake, feed conversion ratio, hepatosomatic index, condition factor, and dress-out were equivalent among treatments. Plasma cortisol, lactate, and osmolality levels were not affected by rearing density, and values were within basal ranges reported for juvenile cobia. Fillet drip-loss did not vary among treatments, but rigor mortis developed more rapidly among fish reared at high density. Rearing juvenile cobia at high densities may reduce growth performance and may influence the timing of rigor development.