| Feeding experiments were conducted to evaluate the nutritional physiology of pyridoxine,myo-inositol and pantothenic acid for cobia Rachycentron canadum. The dietary requirements of pyridoxine,myo-inositol and pantothenic acid for juvenile cobia were estimated in indoor culture system. Results of the present study are presented as follows:1.A 9-week feeding experiment was conducted to quantify the dietary pyridoxine (PN) requirement of juvenile cobia. Basal diet was formulated using vitamin-free casein, gelatin and fish protein concentrate as the protein source. The graded levels of PN ( 0, 2, 4, 8, 16 and 32 mg/kg diet) were added to the basal diets to formulate six experimental diets containing 0.22, 1.89, 3.87, 7.54, 14.75 and 29.88mg PN/kg diet, analyzed by HPLC, respectively. Each diet was fed to three replicate groups of cobia in 250L tanks for 9 weeks, and each tank was stocked with 25 fish (initial weight: 3.23±0.06g). The water salinity was from 30‰to 34‰, temperature fluctuated from 28 to 32℃and dissolved oxygen was above 7mg/l. The results showed that specific growth rate (SGR) have an increasing trend with the increase of dietary pyridoxine (from 0.22 to 3.87mg/kg), but no significant differences were observed among diets containing 3.87mg/kg PN or above. The contents of PN and AST in liver of fish fed diets with 3.87mg/kg were significantly higher than those in fish fed the diets with lower than 3.87mg/kg PN. However, there were no significant differences among diets containing 3.87~29.88mg/kg PN. The contents of PLP and the activities of ALT in the diet with 7.54 mg/kg PN significantly higher than the diets with less than 7.54 mg/kg PN, however, no significant differences were found among diets containing more than 7.54 mg/kg PN. The dietary pyridoxine requirement was estimated to be 3.09~6.87mg/kg by the broken-line model based on the SGR, the hepatic PN, the hepatic PLP, the activities of ALT and AST in fish liver.2. A 9-week feeding experiment were conducted to determine the dietary inositol requirement of juvenile cobia. Basal diet was formulated using vitamin-free casein, gelatin and fish protein concentrate as the protein source. Inositol was supplemented at 0, 0 + antibiotic (0.5%), 100, 200, 400,800 and 1600 mg/kg diet in the basal diet providing0, 0, 96 193, 386, 764 and 1582 mg/kg diet. Each diet was fed to triplicate groups of fish, and each tank (250L) was stocked with 25 fish (initial weight: 3.23±0.06g). The water salinity was from 30‰to 34‰, temperature fluctuated from 28 to 32℃and dissolved oxygen was above 7mg/l during the experiment. The results showed that the intestinal microbial synthesis was not a significant source of inositol for juvenile cobia. Specific growth rate (SGR) significantly increased with the increasing dietary inositol from 0 to 386mg/kg diet. When the inositol level was or more than 386 mg/kg diet, there was no significant difference in SGR (2.78~2.97%/d) among dietary treatments. Broken-line regression analysis of SGR and liver inositol content showed that juvenile cobia require 351.0~363.4 mg inositol /kg diet.3. A 9-week feeding experiment was conducted to quantify the dietary pantothenic acid (PA) requirement of juvenile cobia. Basal diet was formulated using vitamin-free casein, gelatin and fish protein concentrate as the protein sources. The graded levels of PA ( 0, 5, 10, 20, 40 and 80 mg/kg diet) were added to the basal diets to formulate six experimental diets containing 0.12,4.88,9.75,18.47,36.54 and 74.56 mg PA/kg diet, respectively. Each diet was fed to three replicate groups of cobia in 250L tanks for 9 weeks, and each tank was stocked with 25 fish (initial weight: 3.23±0.06g). The water salinity was from 30‰to 34‰, temperature fluctuated from 28 to 32℃and dissolved oxygen was above 7mg/l. The results showed that specific growth rate (SGR) have an increasing trend with the increase of dietary PA (from 0.12 to 18.47mg/kg), but no significant differences were observed among diets containing 18.47mg/kg PA or above(2.82~2.95%/day). Hepatic total pantothenic acid concentration (TP)increased with increasing dietary PA up to 18.47 mg/kg (p<0.05), and then leveled off(p>0.05).Hepatic lipid concentration was highest in the pantothenic acid-deficient fish than those of other dietary groups, and no significant differences were observed among the other dietary treatments (p>0.05). On the basis of SGR and TP, the optimum dietary pantothenic acid requirements of cobia were estimated using broken-line regression analysis to be 16.39~18.87mg/kg diet. |
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