Effects Of Dietary Carbohydrate Levels On Growth Performance, Physiological Status And Body Composition Of Turbot (Scophthalmus Maximus Linnaeus) And Japanese Flounder (Paralichthys Olivaceus)

Feeding trials were conducted to investigate the effects of dietary carbohydrate on growth performance, physiological status and body composition of turbot (Scophthalmus maximus Linnaeus) and flounder (Paralichthys olivaceus). The experiments were conducted in indoor culture system, four isonitrogenous and isolipidic diets( crude protein, 49.35±0.14%,crude lipid, 10.80±0.11%)containing 15.0 %, 18.5%, 22.0% and 25.5% carbohydrate (%/dry matter) was fed to the experimental fish. During the experimental period, the water temperature ranged from 15 to 18°C, the salinity from 28.5 to 32 and the dissolved oxygen content was approximately 7 mg l?1. Results of the study are presented as follows:1. Three 9-week growth trials were conducted to determine the effects of dietary carbohydrate on growth performance, physiological status and body composition of turbot with average initial body weights (4.30±0.01) g (Trial I), (89.57±0.32) g (Trial II) and (208.30±0.29) g (Trial III). There were no significant differences in survival (SR), feed intake ratio (FR), feed efficiency ratio (FE), condition factor (CF), liver glycogen, muscle glycogen, blood glucose and body composition among dietary treatments in Trial I, II and III (P>0.05). In Trial I, the specific growth rate (SGR), viscera index (VSI) and hepatosomatic index (HSI) significantly decreased with increasing dietary carbohydrate levels (P<0.05). The SGR and VSI of the fish fed the diet containing 15.5% carbohydrate was significantly higher than those of the fish fed the diet containing 22.0% and 25.5% carbohydrate (P<0.05), and the HSI of the fish fed the diet containing 15.5% carbohydrate was significantly higher than those of the fish fed the diet containing 25.5% carbohydrate (P<0.05). The SGR, VSI and HIS showed no significant difference among dietary treatments in Trial II and III (P>0.05). In Trial III, the entero-amylase (AMS) of the fish fed the diet containing 18.5% carbohydrate was significantly higher than those of the fish fed the diets containing 22.0% and 25.5% carbohydrate (P<0.05), and the AMS of the fish fed the diet containing 15.0% carbohydrate was significantly higher than those of the fish fed the diets containing 22.0% carbohydrate (P<0.05). Results of the experiment suggest that adult turbot can tolerate higher carbohydrate than juvenile turbot. The optimal carbohydrate level for juvenile turbot (initial body weights 4.30±0.01g) is below 15.0%, and adult turbot (initial body weights 89.57±0.32g and 208.30±0.29 g) can tolerate 25.5% carbohydrate in diets without affecting growth performance, physiological status and body composition obviously.2. Four experimental diets were randomly fed to triplicate groups of Japanese flounder (average initial body weights: 4.96±0.02g) for 9 weeks. The effects of dietary carbohydrate on growth performance, physiological status and body composition were determined. Survival (SR), specific growth rate (SGR), feed intake ratio (FR), feed efficiency ratio (FE), condition factor (CF), liver glycogen, muscle glycogen, blood glucose, hepatosomatic index (HSI) and body composition showed no significant difference among dietary treatments (P>0.05). The VSI of the fish fed the diet containing 18.5% carbohydrate was significantly higher than those of the fish fed the diets containing 25.5% carbohydrate (P<0.05). Results of the experiment showed that no adverse effect was found on the flounder fed the diets containing 25.5% of carbohydrate. The results suggested that flounder can tolerate 25.5% carbohydrate in diets without affecting growth performance obviously.