| Under controllable indoors exprimental conditions, the present paper was involved in as the systematical investigation of nutrient physiology of lipid and fatty acids in juvenile yellow catfish Pelteobagrus fulvidraco. Results of the present study were presented as followed:(1) Morphometrical parameters, nutrient composition, fatty acid profiles of muscle and ovary was investigated in yellow catfish P. fulvidraco during the IV stage. Viscerosomatic index, hepatosomatic index, intraperitoneal fat ratio and gonadosomatic index were relatively high, which were7.93%,1.80%,1.91%and11.27%, respectively. Crude protein contents in muscle, liver and ovary were17.05%,12.49%,20.01%, respectively. The crude lipid contents in these tissues were3.20%,6.61%and10.63%, respectively. The dominant fatty acids of saturated fatty acids, monounsaturated fatty acids, n-6and n-3fatty acids in muscle and ovary were palmitic acid, oleic acid, arachidonic acid and dososahexaenoic acid (DHA), respectively. The ratios of n-3to n-6in ovary were higher than that in muscle.(2) Three isonitrogenous experimental diets were formulated to determine the effect of dietary lipid levels on growth performance, hepatic fatty acid profiles and intermediary metabolism of juvenile yellow catfish P. fulvidraco. Corn oil was added to the diets at the inclusion levels of0,6%and12%, respectively. The experiment continued for8weeks. Dietary lipid levels showed no significant effects on survival of the fish species. The highest weight gain, specific growth rate and protein efficiency rate, the lowest feed conversion rate were observed in fish fed the diet containing6%of dietary lipids(P<0.05). Condition factor, hepatosomatic index, viscerosomatic index and intraperitoneal index increased with increasing dietary lipid levels. Lipid contents in whole body and liver increased with increasing dietary lipid levels, but moisture, and ash contents declined with the incremental dietary lipid levels. Crude protein content in whole body was the highest in fish fed the8.6%of dietary lipid. Increasing18:2n-6and total n-6fatty acid contents, and reducing hepatic DHA content and total n-3fatty acids contents were observed with increasing dietary lipid levels.(3)The effect of dietary LNA to LA ratio on growth performance, hepatic fatty acid profile and intermediary metabolism of juvenile yellow catfish P. fulvidraco was investigated. Five isonitrogenous and isolipidic diets were formulated to contain incremental levels of LNA from0to5%at the expernse of corn oil (rich in LA), resulting in five dietary treatments with LNA to LA ratios ranging from0.35to14.64. The expeirment continued for7weeks. Best growth and feed intake, the lowest feed conversion rate were obtained in the fish fed the diets containing the LNA to LA ratios of1.17and2.12. Dietary LNA to LA ratios significantly influenced viscerosomatic index and hepatosomatic index, but not condition factor. Body composition was also significantly influenced by dietary LNA to LA ratios. Generally, liver FA compositions reflected dietary FA profiles. Declining LA and increasing LNA contents in liver were observed with the increasing dietary LNA to LA ratios. EPA and DHA increased with the increasing LNA to LA ratios, suggesting that yellow catfish could elongate and desaturate C18PUFA into highly unsaturated fatty acids. As a consequence, the n-6fatty acids (FA) declined, and total n-3FA and n-3/n-6ratios increased with the dietary ratios of LNA to LA. Dietary LNA to LA ratios significantly influenced several enzymatic activities involved in hepatic intermediary metabolism, such as lipoprotein lipase, hepatic lipase, pyruvate kinase, succinate dehydrogenase, malic dehydrogenase and lactate dehydrogenase, suggesting that dietary LNA to LA ratios had significant effects on nutrient metabolism in the liver. To our knowledge, this was the first demonstration of the effects of dietary LNA to LA ratios on the enzymatic activities of liver in fish, which provided information on diet quality and utilization, and could also be used as an indicator of the nutritional status of this fish.(4) Six isonitrogenous (crude protein,35%) and isolipid (9%) diets were formulated to use fish oil, corn oil, soybean oil, lineseed oil, palmitic oil and rapeseed oil as lipid sources, respectively. Growth performance, feed utilization and muscle fatty acid profiles were investigated in yellow catfish P. fulvidraco fed six experimental diets for8weeks. The highest weight gain and specific growth rate were observed in fish fed the diet containing fish oil and lineseed oil. The lowest feed conversion ratio were observed in fish fed the diet containing fish oil and corn oil (P<0.05). Lipid contents in whole body were significantly higher in fish fed the diet containing fish oil and corn oil than those of fish fed the diets containing lineseed oil, palmitic oil and rapeseed oil, respectively (P<0.05). Hepatic lipid contents in the groups of corn oil and rapeseed oil were significantly higher than those in lineseed oil and palmitic oil groups. Fatty acid profiles in muscle reflected dietary fatty acid profiles.(5) Six isonitrogenous and isolipidic experimental diets were formulated to determine the effect of partial replacement of fish oil by corn oil on growth performance, hepatic fatty acid profiles and intermediary metabolism of juvenile yellow catfish P. fulvidraco. Corn oil was added to diets at the inclusion level of0,1%,2%,3%,4%and5%to replace0,20%,40%,60%,80%and100%of fish oil, respectively. The experiment continued for8weeks. The highest weight gain and specific growth rate were observed in fish fed the diet with60%of fish oil replaced by corn oil (P<0.05). The lowest feed intake and feed conversion rate, and the highest protein efficiency rate were observed in fish fed the diet with20%of fish oil replaced by corn oil (P<0.05). The replacement of fish oil by corn oil showed no significant effect on moisture, crude protein and ash contents in whole body and muscle, but significantly influenced crude lipid contents of whole body and muscle. Generally speaking, hepatic fatty acid profiles reflected dietary fatty acid profiles. Increasing hepatic linoleic acid and total n-6fatty acid contents, reducing linolenic acid, EPA and DHA contetns were observed in fish with increasing dietary inclusion level of corn oil. The ratio of n-3to n-6fatty acids significantly reduced with increasing dietary com oil levels. Hepatic SDH and LDH activities increased with increasing dietary corn oil levels (P<0.05), but MDH, LPL and HL activities showed no significant differences among the treatments (P>0.05).(6) The effect of dietary conjugated linoleic acid (CLA) on growth performance, body composition and hepatic intermediary metabolism was investigated in juvenile yellow catfish P. fulvidraco. The five isonitrogenous (35%crude protein) experimental diets were formulated to contain graded CLA levels of0(control),0.5%,1%,1.5%and 2%, respectively. Three replicated groups of fish were fed to satiation, twice a day, over a period of8weeks with CLA oil, containing mainly the bioactive cis-9, trans-11and trans-10, cis-12isomers. The increase of dietary CLA levels reduced specific growth rate, feed conversion rate, condition factor, hepatosomatic index and viscerosomatic index of yellow catfish. Increasing dietary CLA levels significantly reduced lipid contents in whole body and liver. The dietary inclusion of CLA modified total percentages of the main groups of fatty acids. Increasing saturated fatty acid content and reduced18:1fatty acid and mono-unsaturated fatty acid contents in whole body were observed with increasing dietary CLA inclusion. Increasing dietary polyunsaturated fatty acids were observed in fish fed the diet containing increasing CLA. However, arachidonic acid, eicosapentaenoic acid and docosahexaenoic acid showed no significant differences among the treatments (P>0.05). Dietary CLA supplementation resulted in a significant increase of the trans-10, cis-12and cis-9, trans-11CLA isomers in whole body, and also significantly influenced several hepatic enzymatic activities, such as SDH, LDH, MDH, LPL and HL activities. These indicated that despite promoting the CLA and PUFA deposition in whole body, dietary CLA supplementation should be carefully evaluated in intensive yellow catfish farming as it reduced growth performance and feed utilization. |
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