EFFECTS OF DIETARY-LIPID AND CARBOHYDRATE-LEVELS ON GROWTH AND BODY-COMPOSITION OF JUVENILE RED DRUM, SCIAENOPS-OCELLATUS

Juvenile red drum (2.9 +/- 0.3 g) were fed one of six experimental diets (containing fish meal, crab meal, fish oil, wheat middlings, mineral and vitamin supplements, cellulose filler and binder) that provided 32% crude protein and 6 or 10% lipid, at three gross-energy (GE) levels (15.8 +/- 0.3, 17.1 +/- 0.2 and 18.7 +/- 0.3 kJ/g). Dietary carbohydrate (NFE) levels ranged from 24 to 39%. Significantly (P < 0.05) higher weight gain (481%), feed efficiency (FE: 0.375), apparent net protein retention (ANPR: 19.77%) and apparent net energy retention (ANER: 10.81%) were associated with a diet containing 16.1 kJ GE/g, 10% lipid and 24% NFE. Survival (71-88%) did not differ significantly among dietary treatments. Weight gain, FE, ANPR and ANER of red drum was inversely related to dietary energy level and dietary carbohydrate content. Body lipid levels were significantly (P < 0.05) higher in fish fed 10% lipid diets than in those fed 6% lipid. Dietary lipid exhibited greater protein-sparing action than dietary carbohydrate, at all energy levels tested. The ability of juvenile red drum to utilize dietary carbohydrate as an energy source may be limited in comparison with warmwater omnivorous species like channel catfish and common carp.