Study On Dietary Lipid And Essential Fatty Acid Requirement In Advanced Juvenile Tilapia(Oreochromis Niloticus)

The studies were conducted to investigate the effects of dietary lipid level and essential fatty acid level [mainly linoleic acid(LA) and linolenic acid(LNA)], on growth performance, body composition, fatty acid composition, serum biochemical and lipid metabolism enzymes activities in Nile tilapia and GIFT,Oreochromis niloticus. The aim of these studies were to deduce the optimal dietary lipid level, essential fatty acid level and LA to LNA ratio for the best growth performance of advanced juvenile Nile tilapia and GIFT. The contents and results are as follows:1. An8-week feeding experiment was conducted to evaluate the optimal dietary lipid requirement of advanced juvenile O. niloticus. In this experiment,360fish with average initial body weight of (46.14±4.67)g were randomly divided into6groups with4replicates of15fish in each replicate. Six groups were fed diets with0%(control group),3%,6%,9%,12%,15%fish oil, respectively (measured lipid level of six diets were0.20%,2.70%,6.11%,8.04%,11.13%and14.85%, respectively). After the8-week feeding trial, growth performance, lipid deposition, serum biochemical indexes and lipid metabolism enzymes activities were measured. The results showed as follows:with the increase of dietary lipid levels, weight gain rate(WGR), specific growth rate(SGR) and protein efficiency ratio(PER) of O. niloticus were increased at first and then decreased, whereas the feed conversation ratio(FCR) was firstly decreased and then increased. Second-order regression analysis showed the best dietary lipid level which could acquire the best WGR, FCR and PER was8.86%,9.75%and9.40%, respectively. The increase of dietary lipid levels had significant role in increasing hepatosomatic index(HSI), and crude fat content of whole body and muscle(P<0.05). With the increase of dietary lipid levels, contents of total cholesterol(TCHO) and triglyceride(TG) in serum were increased at first and then decreased, and high density lipoprotein cholesterol(HDL-C) content was firstly increased and then maintained at a steady state. Broken-line regression analyses of the HDL-C content against dietary lipid level indicated that the dietary lipid requirement for optimal HDL-C content was8.30%. The activities of alanine aminotransferase(ALT) and aspartate aminotransferase(AST) got the maximum at the11.13%dietary lipid level., and got the minimum at the6.11%level. In the respect of lipid metabolism enzymes, with the increase of dietary lipid levels, the activities of intestine lipase, lipoprotein lipase(LPL), hepatic lipase(HL) and total lipase(TL) tended to increase at first and then decrease, and fatty acid synthase (FAS) activity was decreased significantly (P<0.05). According to the comprehensive analysis on growth performance, body composition, serum biochemical indexes and lipid metabolism enzymes activities, it was concluded that the optimal dietary lipid requirement of advanced juvenile O. niloticus should be8.30%-9.75%.2. An10-week feeding experiment was conducted to evaluate the optimal dietary linoleic acid (LA) requirement of advanced juvenile GIFT O. niloticus. In this experiment,630fish with average initial body weight of (60.98±0.64)g were randomly divided into7groups with3replicates of30fish in each replicate. Seven diets with a constant dietary lipid level(8%) were formulated to contain different levels [0.07%(control group),0.36%,0.61%,1.03%,2.00%,3.00%,4.15]of LA, by supplementing corn oil and palmitic acid to modulate the fatty acid content. Fish were fed three times daily (8:30,12:30and16:30) to apparent satiation. At the end of feeding trial, growth performance, body composition, serum biochemical indexes and fatty acid composition were measured. The results showed as follows:with the increase of LA levels, weight gain rate(WGR) of GIFT were increased at first and then decreased. Second-order regression analysis showed the best LA level which could acquire the best WGR was2.49%. Broken-line regression analyses of FER against dietary LA level indicated that the dietary LA level for best FER was1.94%. Serum total cholesterol(TCHO) and triglyceride(TG) levels first decreased then increased as the level of LA increased, and were lowest in the group fed1.03%LA. While, high density lipoprotein cholesterol(HDL-C) content was firstly increased and then decreased as the level of LA increased, and were highest in the group fed1.03%LA, treatment groups were significant higher than control group(P<0.05). Low density lipoprotein cholesterol(LDL-C) content decline as the level of LA increased. There was significant correlation between GIFT issue and dietary fatty acid composition. With the decreased of dietary saturated fatty acids(SFA) level, muscle and liver SFA level also declined. With the increase of LA levels, n-6fatty acids level in muscle and liver also rose, while n-3fatty acids level declined. Our comprehensive analysis of growth performance, serum biochemical indexes and fatty acid composition in muscle and liver suggests that the optimal level of dietary LA for advanced juvenile GIFT O. niloticus is between1.03% and2.49%.3. An10-week feeding experiment was conducted to evaluate the optimal dietary linoleic acid(LA) and linolenic acid(LNA) levels of advanced juvenile GIFT O. niloticus. Six hundred and thirty fish with average initial body weight of60.74±0.89g were randomly divided into7groups with3replicates of30fish in each replicate. Seven diets with a constant dietary lipid level (about8%) were formulated to contain different LA levels(1%,2%,3%) and LNA levels(0%,0.5%) by supplementing corn oil, flaxseed oil and palmitic acid to modulate the fatty acid content. Fish were fed three times daily (8:30,12:30and16:30) to apparent satiation. At the end of feeding trial, growth performance, serum biochemical indexes and fatty acid composition were measured. Final weight(FW) and weight gain rate(WGR) which got the maximum at2%dietary LA level increased with the dietary LA level rose. While, adding0.5%dietary LNA level had no significant effect on FW, WGR and FER (P>0.05) and had significant effect on serum triglyceride(TG) and low density lipoprotein cholesterol(LDL-C) contents(P<0.05). Serum total cholesterol (TCHO) and high density lipoprotein cholesterol(HDL-C) was not influenced by dietary LA level and LNA level (P>0.05). Adding0.5%dietary LNA level elevated the content of n-3fatty acid including18:3n3,20:5n3,22:5n3and22:6n3significantly (P<0.05), and reduce the n-6/n-3ratio significantly at the same time (P<0.05). In conclusion, we suggests that adding0.5%LNA level in diet is essential for advanced juvenile GIFT O. niloticus.4. An10-week feeding experiment was conducted to evaluate the optimal dietary LA/LNA ratio of advanced juvenile GIFT O. niloticus. Three hundred and sixty fish with average initial body weight of60.98±0.64g were randomly divided into4groups with3replicates of30fish in each replicate. Four diets with a constant dietary lipid level(8%) were formulated to contain different LA/LNA ratios (1.24,1.94,3.44,4.93) by supplementing corn oil, flaxseed oil and palmitic acid to modulate the fatty acid content. Fish were fed three times daily (8:30,12:30and16:30) to apparent satiation. At the end of feeding trial, growth performance, body composition, serum biochemical indexes and fatty acid composition were measured. The results showed as follows:with the increase of dietary LA/LNA ratio, weight gain rate(WGR) of GIFT were increased at first and then decreased. Second-order regression analysis showed the best dietary LA/LNA ratios which could acquire the best WGR and FER were3.73and3.41respectively. There was no significant differences in survival rate and hepaticsomatic index(HSI)(P>0.05). Viscerasomatic index(VSI) in group3and4were significant higher than group1and2(P <0.05). Serum total cholesterol(TCHO) and triglyceride(TG) contents first decreased then increased as the dietary LA/LNA ratio increased, and were lowest in group3. High density lipoprotein cholesterol(HDL-C) content in group4showed significant lower than other groups(P<0.05). Low density lipoprotein cholesterol(LDL-C) firstly decreased and then increased as the dietary LA/LNA ratio increased, and were lowest in group3. Muscle and liver saturated fatty acids(SFA) level declined as the dietary SFA level decreased. With the increase of dietary n-6fatty acids level, n-6fatty acids level in muscle and liver also rose, while n-3fatty acids level declined. n-6/n-3ratio in muscle and liver increased significantly as the increase of dietary LA/LNA ratio(P<0.05). In conclusion, we suggests that the optimal dietary LA/LNA ratio for advanced juvenile GIFT O. niloticus is between3.41and4.93.