A shrimp protein hydrolysate (SPH) containing 894.2 g kg À1 crude protein (CP) and 54.3 g kg À1 total lipids was tested as a partial replacement for fish meal (FM) in diets of juvenile cobia. The effects of increasing dietary levels of SPH on the survival, weight gain (WG), specific growth rate (SGR), feed conversion ratio (FCR), nitrogen retention efficiency (NRE) and daily feed intake (DFI) of cobia with initial body weight of 11.9 g were evaluated. Four isoproteic (from 431.1 to 439.7 g kg À1 ) and isoenergetic (20 825-21 347 MJ kg À1 ) diets were formulated to contain 0 (Control), 120, 240 or 360 g kg À1 of dietary CP derived from SPH. Survival, WG, SGR, FCR, NRE and DFI ranged from 90 to 100%, 40.2-56.5 g, 4.7-6.1% day À1 , 1.04-1.54, 26.3-44.0% and 4.7-6.0% fish À1 day À1 respectively. Survival and DFI were not affected by the dietary treatments. On the other hand, fish fed the control diet and the one containing 120 g kg À1 SPH had higher WG, SGR and FCR. Nitrogen retention efficiency was significantly higher for fish fed diets 0 and 120. It is concluded that up to 120 g kg À1 of SPH in cobia diets can be used with no significant effects on feed utilization and fish performance.

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 driploss 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.