Effects Of Different Dietary Lipids On Growth, Lipid Metabolism And Antioxidant Responses Of Blunt Snout Bream Fingerlings

Blunt snout bream(Megalobrama amblycephala) is an herbivorous freshwater fish native to China. As a very important economic species in china, it has been widely favored for its fast growth, tender flesh, and high disease resistance. Dietary lipid is one of important nutrients for fish growth, which works as a source of energy and essential fatty acid. It also improves growth in both larvae and early fingerlings and contributes to healthy and efficient breeding in both sub-adult and adult of fish. At present, previous studies mainly concern about the effects of different lipid source on growth performance, proximate composition and oxidative stress in sub-adult and adult of blunt snout bream, but information is quite scarce on different lipid source influencing lipid deposition and metabolism in larvae and early fingerlings. Therefore, it is important to systematicly study on the requirement of dietary lipid in early stage of blunt snout bream.In this study, in order to ensure a healthy growth and development of blunt snout bream in farmed fish, a series of feeding trials were conducted to determine the optimal demand of lipid in this fish. The first investigation was evaluated the effects of different dietary lipid sources on growth performance, antioxidant responses, peroxisome proliferator-activated receptors(PPARs) gene expression levels and fatty acid composition in the blunt snout bream fingerlings. Then, the effects and mechanisms of different soybean oil levels on lipid metabolism in blunt snout bream fingerlings were investigated. The main results that this study had are as follows:1. Effects of different dietary lipid sources on growth performance, fatty acid composition, PPAR gene expressions and antioxidant responses of blunt snout bream fingerlings First, five experimental diets, which respectively contained soybean oil(SO), fish oil(FO), peanut oil(Pe O), canola oil(CO) and palm oil(Pa O), were fed to blunt snout bream fingerlings(mean initial body weight, 0.35 ± 0.01 g) for 60 days. The results of this study showed that fish fed SO and FO diets were higher on body weight gain(BWG), specific growth rate(SGR) than in the other groups, but feed conversion ratio(FCR) did not have significantly difference among treatments. Compared with vegetables oil groups, a significantly lower hepatic lipid content and significantly higher hepatic eicosapentaenoic acid(EPA) and docosahexaenoic acid(DHA) concentrations of fish were found in FO group. The hepatic expression of PPAR-α and PPAR-γ of fish in vegetable oil groups were significantly upregulated compared with FO. The activities of catalase(CAT), superoxide dismutase(SOD), and glutathione peroxidase(GPx) and the value of malondialdehyde(MDA) in livers by feeding Pa O diet were significantly lower than other groups. These results indicated that SO diets could meet the requirement of fatty acids for blunt snout bream fingerlings. But we thought significant increase content of liver lipid deposition might be might be observed if this trial could be continued for a longer time.2. Effects of different dietary phospholipid levels on growth, fatty acid composition, PPAR gene expressions and antioxidant responses of blunt snout bream fingerlings Dietary phospholipids(PL) are essential for normal growth and survival of fish larvae. Therefore, the second feeding trial was conducted to evaluate the optimal demand of the optimal demand of PL in blunt snout bream fingerlings. Fish were put into five groups that fed five different experimental diets formulated with PL at inclusion levels of: 0, 2, 4, 6 and 8 % for 60 days. It turned out that final body weight, BWG and SGR increased significantly as dietary PL level increased from 0 to 6 %. The expression levels of PPAR-α and PPAR-γ and the hepatic activities of CAT, SOD and GPx of fish were significantly increased with dietary PL supplementation from 0 to 6 %. Meanwhile, the liver MDA value of fish in PL6 groups was lower than the control. These data suggested that that supplementation of 6 % PL in diet could help to growth performance improvement and the antioxidant defense increasing in blunt snout bream fingerlings. Therefore, it suggested that the optimum level of dietary PL in blunt snout bream fingerlings was 6 %.3. Effects of different dietary soybean oil levels on growth, lipid deposition, tissues fatty acid composition and hepatic m RNA levels of genes involved in lipid metabolism in blunt snout bream fingerlings Thus, the third feeding trial was further conducted to evaluate the effects of dietary soybean oil(SO) on hepatic lipid deposition and metabolism in blunt snout bream fingerlings. Five experimental diets containing SO at inclusion levels of 0, 20, 32, 56 and 100%, and a diet containing 100% fish oil(100%FO) were fed for 9 weeks. The BWG of fish in 20%SO and 100%FO groups were significantly higher than in the other groups. The content of lipid and linoleic in the liver and muscle were increased with incremental dietary SO level. Meanwhile delta-9 acyl-Co A desaturase were up-regulated and PPAR-α and PPAR-β were down-regulated with increasing dietary SO level. It indicated that supplementation of 20% SO could help blunt snout bream fingerlings growth to improve. However, an excess of linoleic in SO supplemented diets influenced the m RNA levels of lipid metabolism-related genes which induced lipid deposition.4. Effects of feed soybean oil levels on serum biochemistry indexes, hepatic antioxidant responses and fatty acid composition of liver and intestine in blunt snout bream fingerlings Furthermore, the finally feeding trial was further conducted to evaluate the effects of dietary SO on lipid deposition and healthy aquaculture in blunt snout bream fingerlings. Three experimental diets respectively containing 0%, 20%, and 100% SO and a diet containing 100% FO were fed for 15 weeks. Higher activities of CAT, SOD and GPx were showed in liver of fish fed 20%SO diet. The content of lipid and linoleic in the liver and intestine were increased with incremental dietary SO level. The activities of lipoprotein lipase, glutamic oxalacetic transaminase, and glutamic-pyruvic transaminase and the content of triglyceride, total cholesterol and very low density lipoprotein in serum of fish fed 100%SO diet were significantly higher than in the other groups. It indicated that supplementation of 20% SO could help to increasing the antioxidant defense in blunt snout bream fingerlings. However, an excess of linoleic in SO supplemented diets would induce a serious lipid deposition in tissues, which could affect the normal lipid metabolism and increase organism damage.In summary, we proposed that a combination of PL and SO diet should be used in feed formulations, which could increase the growth performance and insure normal development in blunt snout bream fingerlings. But higher doses of SO supplementation in the diet increased lipid deposition in liver.