| Feeding trials were conducted to examine the effects of dietary carbohydrate source and level on growth, feed utilization, body composition and related enzyme activities of golden pompano, Trachinotus ovatus. Results of the present study are presented as follows:1. In this trial, five isonitrogenous and isolipidic diets were formulated to contain 20% of glucose, sucrose, dextrin, corn starch and gelatinized corn starch. The fish (31.24±0.58 g initial weight) were fed each diet for 8 weeks. Then the effects of different carbohydrate sources on growth, body composition, plasma biochemical indices and glycolytic enzyme activities were compared to find out the optimum carbohydrate sources. The results showed that different carbohydrate sources significantly affected the weight gain (WG) and specific growth rate (SGR) (P<0.05). The WG and SGR increased with the increasing carbohydrate molecule. And the group fed with gelatinized corn starch were the highest (335.35% and 2.62%d"’, respectively). The viserosomatic index (VSI), hepatosomatic index (HSI), liver glycogen content and muscle glycogen content of the five carbohydrate groups were significantly different (P<0.05), and those of glucose group were the highest. Different carbohydrate sources also significantly affected the plasma glucose, total cholesterol and triglycercide (P<0.05). The results of digestive enzymes analysis indicate that dietary carbohydrate sources had significant effects on digestive enzyme activities (P<0.05). The protease activities of the two starch groups were significantly lower than the other three groups (P<0.05). The fish fed with sucrose had the highest amylase activity, significantly higher than the others (P<0.05). The lipase activity increased with the increasing dietary carbohydrate molecule, that of gelatinized corn starch group was the highest. No significant difference was observed in hepatic hexokinase (HK) activity among dietary groups (P>0.05). Activities of glucokinase (GK), pyruvate kinase (PK) and phosphofructokinase (PFK) reached the highest in the glucose group (P<0.05).2. An 8-week feeding trial was conducted to investigate the effects of dietary carbohydrate level on growth, feed utilization, body composition and digestive enzyme activities of Trachinotus ovatus, with an average body weight of (31.24±0.58) g. Six fishmeal based diets with varying carbohydrate levels of 0%, 6.5%,13%,19.5%,26% and 32.5%, respectively were tested. The results showed that the WG, SGR and Feed efficiency (FE) significantly increased first and then significantly decreased (P<0.05) with the increasing of dietary carbohydrate levels. The diet with carbohydrate level of 13% had the highest WG, SGR and FE, which were 330.98%,2.61% and 0.96 respectively. The contents of body moisture, crude protein, crude lipid and ash were all significantly affected by the different dietary carbohydrate levels (P<0.05). And the contents of HIS and liver glycogen significantly increased with the increasing of dietary carbohydrate levels. Dietary carbohydrate levels had remarkable influence on protease and amylase activities (P<0.05), while did not on the activity of hexokinase (HK). With the increasing of dietary carbohydrate levels, apparent digestibility (ADC) of carbohydrate increased first and then significantly decreased (P<0.05). The ADC of protein and lipid of the groups at low dietary carbohydrate levels were higher than that of the groups at high dietary carbohydrate levels. Regression analysis showed that dietary carbohydrate level at 19.8% generated the highest SGR.In conclusion, the present study suggests that the effect of macromolecule (starch) on growth of Trachinotus ovatus is better than glucose, sucrose and dextrin, and the gelatinized corn starch has the best growth promotion effect. The regression model analysis shows that the optimal dietary carbohydrate level which can make Trachinotus ovatus acquire the best specific growth rate is 18.52. |
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