| Part 1 A 12-week feeding trial in a flow-through system was conducted to determine the effects of dietary choline levels on growth performance, feed utilization and body composition of juvenile starry flounder (Platichthys stellatus, Pallas 1788) (initial average body weight:36.69±0.04g). The basal diet was formulated using casein, soy protein concentrate and gelatin as the main protein source and fish oil as the lipid source, respectively. Graded levels of choline chloride were supplemented to the basal diet to formulate six isonitrogenous and isoenergetic diets containing 826.87 (control group),1160.99,1462.54,2096.55,3337.11 and 4606.36 mg choline/kg diet, respectively. The results showed that weight gain rate (WGR) and specific growth rate (SGR) were increased obviously as dietary choline increased from 826.87 to 2096.55 mg/kg diet (P<0.05), whereas no differences were found with further increase of choline levels. Neither survival rate (SR) nor condition factor (CF) was affected by choline levels(P>0.05). Although daily feed intake (DFI) of other experimental groups were increased significantly compared with control group as dietary choline increased (P<0.05), the values were not significant differences with each other (P> 0.05). Feed conversion ratio (FCR) decreased significantly (P<0.05) with increasing dietary choline levels. Protein efficiency ratio (PER) and protein retention efficiency (PRE) increased significantly, and the values reached the maximum in fish fed 2096.55 mg choline/kg diet, and subsequently values were lower as dietary choline increased. Hepatosomatic index (HSI) and viscerosomatic index (VSI) were significantly decreased (P<0.05) as dietary choline increased. There were no statistical differences in whole body composition among different treatments (P> 0.05). Muscle lipid content was increased obviously as dietary choline increased (P< 0.05), but liver lipid content was decreased at first and increased subsequently, and the value was lower in the fish fed 2096.55 mg choline/kg diet than the others(P<0.05). In this experiment, broken-line analyses of SGR indicated that the optimal dietary choline requirement for juvenile starry flounder was 1891.80 mg choline/kg diet.Part 2 A 12-week feeding trial in a flow-through system was conducted to determine the effects of dietary choline levels on Inosine 5'-monophosphate(IMP) in the muscle, blood lipid metablism and immunological parameters of juvenile starry flounder (Platichthys stellatus, Pallas 1788) (initial average body weight: 36.69±0.04g). The basal diet was formulated using casein, soy protein concentrate and gelatin as the main protein source and fish oil as the lipid source, respectively. Graded levels of choline chloride were supplemented to the basal diet to formulate six isonitrogenous and isoenergetic diets containing 826.87 (control group),1160.99, 1462.54,2096.55,3337.11 and 4606.36 mg choline/kg diet, respectively. The results showed that both the content of IMP in the muscle and serum triglyceride (TG) were increased at first and decreased subsequently, and the values reached the top in fish fed 1462.54mg/kg diet and 2096.55 mg/kg diet respectively. Although serum cholesterol (TCHO) and serum low density lipoprotein (LDL-C) were elevated significantly as dietary choline increased (P<0.05), LDL-C was decreased obviously in fish fed 4606.36mg/kg diet. Activities of aspartate aminotransferase (AST), glutamic-pyruvic transaminase (ALT), alkaline phosphatase (ALP) and lactate dehydrogenase (LDH) in serum were decreased significantly by dietary choline (P< 0.05), and the values increased simultaneously in fish fed diets containing 4606.36mg/kg diet significantly (P<0.05). However, hemoglobin(Hb) concentrations were not affected by choline levels (P>0.05), both serum total protein(TP) and lysozyme(LSZ) were elevated significantly as dietary choline levels increased (P< 0.05). No significant difference was found on superoxide dismutase (SOD) with further increase of choline levels (<4606.36mg/kg diet), but the value was increased obviously in fish fed diets containing 4606.36 mg/kg diet.Part 3 An experiment was conducted to study on the content of inosine 5'-monophosphate (IMP) analyzed by HPLC in the muscle of starry flounder (Platichthys stellatus) (average body weight:485±45g) fed a commercial diet under different storage temperature (19.5±1.0℃,4℃,0℃,-18℃and -70℃) within 30 days. The results showed that the content of IMP in the muscle of starry flounder was increased at first and decreased subsequently, and the values reached the tiptop respectively at 3h (2.397mg/g) and 5h (2.289mg/g) after slaughter when stored at room temperature (19.5±1.0℃) and 4℃, and the values increased by 14.2% and 9.1% compared with 2h after slaughter, then it decreased rapidly as storage progressed. The content of IMP in the muscle was significantly decreased by the storage time when stored at 0℃(ice storage). The content of IMP on 1d after slaughter was 63.2% of that on Od after slaughter, and then it decreased under ice storage (0℃). It can be deduced the content of IMP in the muscle will reached the maximum within 5-24h under ice storage (0℃). Although the content of IMP in the muscle reached tiptop on 1d (2.501mg/g) and 5d (2.375mg/g) after slaughter during storage at -18℃and -70℃respectively, and the values increased by 19.2% and 13.1% compared with Od after slaughter respectively, then the concentration of IMP declined little subsequently and it remained a high level of about 95% of the highest values on the 5th day respectively from 7d to 30d. The results indicated the degradation rate of IMP in the muscle of starry flounder was obviously affected by storage temperature and time, i.e. the higher temperature and the longer time they were, the lower the content of IMP was. |
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