Effects of Carbohydrate and Water Temperature on Nutrient and Energy Digestibility of Juvenile and Grower Rockfish, Sebastes schlegeli

A factorial (4x2x2) experimental design was employed to determine apparent digestibilities of dry matter (DM), protein, lipid, energy and nitrogen-free extract (NFE) of the test diets containing either alpha-potato starch (A-PS), beta-potato starch (B-PS), beta-corn starch (B-CS) or dextrin (DEX) as dietary carbohydrate energy for juvenile (average weight 30 g) and grower (average weight 300 g) rockfish reared at 13 degrees C and 20 degrees C. Chromic oxide was used as an inert marker. Feces were collected by fecal collectors attached to rearing tanks from triplicate groups of juvenile and grower rockfish. Digestibilities of DM, energy and NFE of the test diets were significantly affected by dietary carbohydrate and water temperature (p<0.01), but not by fish size. DM digestibility of the fish fed the A-PS diet was significantly higher than that of fish fed other treatments, except for the DEX diet at 20 degrees C. DM digestibility of rockfish fed the B-CS diet was significantly lower than that of other diets. A similar pattern was observed in apparent digestibility of energy. NFE digestibility of fish fed the test diets was significantly affected by carbohydrate and significantly correlated to DM (r = 0.97, p<0.0 1) and energy (r = 0.99, p<0.01) digestibilities, regardless of water temperature and fish size. NFE digestibility of the fish fed the beta-starch diets was relatively lower compared to that of the alpha-starch diets, and ranged from 35 to 43% and 20 to 27% for B-PS and B-CS, respectively. The present findings indicate that carbohydrate and water temperature significantly affected digestibilities of dry matter, energy and nitrogen-free extract of rockfish. Among dietary carbohydrates, alpha-potato starch could be effectively used as dietary carbohydrate energy for rockfish at 13 degrees C and 20 degrees C.