Effect Of Dietary Non-protein Energy Sources On Fat Deposition And Lipid Metabolism Of Grass Carp(Ctenopharyngodon Idellus)

Production of grass carp(Ctenopharyngodon idellus) is the second large fish species of the world, and constitutes the largest aquaculture industry of finfish in China. As a typical herbivorous finfish, grass carp can eat artificial diets in aquaculture as well as aquatic weeds in natural environment. However, there is a great common phenomenon that the grass carp deposit extensive of fat in fish body when the fish fed commercial diets containing low protein and high lipid and/or carbohydrate levels. In order to explore the fat accumulation and lipid metabolic regulation mechanisms of grass carp, we studied the effects of different dietary non-protein energy source level and dietary supplemention of clofibrate on the growth performance, body composition, lipid deposition site, serum biochemical indices, liver histology and genes expression and enzymes activities involved in lipid metabolism of grass carp, and we also analyzed the fat deposite, physiological and biochemical changes in grass carp fed with vegetable food, broad bean and formulated diet.1. The effects of dietary non-protein energy source levels on growth performance, body composition and fat accumulation in grass carp (Ctenopharyngodon idellus)A study was conducted to analyze the effect dietary non-protein energy source leves on fat accumulation of grass carp.360grass carp (average weight40.10±0.15g) were divided into four groups randomly, each group was triplicate. Four isonitrogenous (300g kg-1)practical diets were formulated to contain four non-protein energy levels (control diet6.52kJ g-1. high-CEL diet5.32kJ g-1、high-CHO diet8.46kJ g-1and high-LIP diet8.54kJ g-1). After rearing for9weeks, the fish were fasted for24h, then six fish were randomly selected from each group, and the growth performance, feed conversion ratio, whole body and tissue composition, biometric parameters and fat deposition were detected. The results show that, compared with the control group, fish fed the high-CHO diet and the high-LIP diet had no significant difference in the growth performance and feed conversion ratio (P>0.05). In contrast, the high-CEL diet containing lower non-protein energy level led to significant lower WG, SGR and PER (P<0.05). The whole body lipid and muscle lipid were significantly increased in fish fed he high-CHO diet and the high-LIP diet (P<0.05), and the high-LIP diet group showed the highest values among the all groups. The opposite appearances were found in the moisture of whole body and muscle. The high-CHO diet group had the highest liver lipid in all groups. The lowest lipid content of whole body, muscle and liver were found in the high-CEL diet group(P<0.05). The high-CHO diet group had the highest HSI among the all groups (P<0.05). The high-LIP diet group had the significantly highest VSI and MFI in the all group (P<0.05). Proportion of fat in muscle (11.46%-14.54%), liver (2.35%-4.85%) and mesentery (22.93%-28.61%) out of the total body fat did not change significantly among treatments. Those results indicated that increasing dietary non-protein energy source levels did not improve the growth, but can increase the fat deposite in fish body.2. The effects of dietary non-protein energy source levels on serum biochemical indices and histology of liver in grass carp {Ctenopharyngodon idellus)The conceptual design of rearing was the same as that of the test One. After the rearing for9weeks, the fish was fasted for24h, then three fish were randomly selected from each group, and the effects of dietary different non-protein energy source levels on serum biochemical indices and histology of liver were detected. The results showed that the triglyceride (TG) and cholesterol (CHO) of the fish fed the high-LIP diet and high-CHO diet were significantly higher than those of the contol group and the high-CELgroup (P<0.05). However, the fish fed the high-CEL diet had the lowest TG and CHO in all the groups. The serum activities of aspartate amninotransferase (AST), alanine aminotransferase (ALT) and alkaline phosphatase (ALP) of the fish fed the high-CHO diet group were significantly higer than those of the control group and the high-CEL group (P<0.05), and there was no significantly different between the high-LIP group and the control group (P>0.05). There was no significantly different of total protein (TP) and blood urine nitrogen (BUN)between the high-CHO diet group, the high-LIP diet group and the control group (P>0.05), but the high-CEL group was markedly lower than that of the control group (P<0.05). The high-CEL group had the highest level blood glucose (GLU) among the all groups (P<0.05). As the aspect of liver histology, the hepatocytes of the fish fed the high-CHO diet were swelling by extreme lipid infiltration, and there were extreme lipid droplets in the cytoplasm, and the nucleus were dislocation, loss of cytoplasm staining affinity. However, the hepatocytes of the fish fed the high-CELdiet were arranged tidy, the nucleus is located in the central of cell, and the size of cell is normal, no fat droplets in cytoplasm. Therefore, the fish fed the high-CHO diet led the poor liver status among the all groups.3. The effects of dietary non-protein energy source levels on the genes expression and enzymes activities involved in lipid metabolism in grass carp (Ctenopharyngodon idellus)This study was to detect the effects of dietary non-protein energy source levels on the genes expression and enzymes activities involved in lipid metabolism of liver and mesenteric adipose tissue of grass carp. The results showed that the activities of fatty acid synthetase (FAS), acetylcoenzyme-A carboxylase (ACC) and glucose-6-phosphate dehydrogenase (G6PD) were significantly elevated in the fish fed the high-CHO diet (P<0.05). Compared with the control diet group, there was a decreasing trend of the FAS, ACC and G6PD activities in the fish fed high-LIP diet and high-CEL diet. There was no significant differnce of malic enzyme (ME) activity among all the groups (P>0.05). The mRNA expressions of FAS and ACC in liver were significantly higher of the high-CHO diet group than those of other group (P<0.05). In the mRNA levels of FAS and ACC there appeared a decreased trend in the high-CEL and high-LIP diet group compared with the control group. The expression of PPARa was significantly higher in the high-CEL diet group than that of the other group (P<0.05). Meanwhie, the LPL mRNA abundant was significantly increased in the fish fed high-CEL diet and high-LIP diet (P<0.05). In the mesenteric adipose tissue, the expression of FAS and ACC had similar tendencies as those in the liver. The LPL gene expression was significantly down-regulated in the high-CEL diet group, but up-regulated in the high-CHO and high-LIP diet group (P<0.05). Those results indicated that although the high dietary carbohydrate and lipid both can induce the lipid deposition in fish, the metabolic mechanism is markedly different.4. The effects of dietary supplemention clofibrate on the body composition, surem biochemical indices and lipid metabolism in grass carp (Ctenopharyngodon idellus)This study was to detect the hypolipidaemic effect of clofibrate in the grass carp fed the high-CHO diet and high-LIP diet. The grass carp was the end of test one fish (average weight205±12g), they were then treated with clofibrate (50mg/kg body weight) in the same high-CHO diet and high-LIP diet for4weeks. Afert rearing4weeks, the fish were fasted for24h, and then body weight, body composition, plasma lipid parameters and lipid metabolism-related genes in liver were measured. The results showed that there were no significant differences in the growth performance of the fish treated with clofibrate (P>0.05). However, there were markedly reduced the VSI and MFI of fish treated with clofibrate (P<0.05), especially the fish fed the high-LIP diet containing clofibrate. Clofibrate treatment decreased the lipid content of whole body, muscle and liver (P<0.05). The plasma contents of TAG, cholesterol, LDL-C and HDL-C were all significantly lowered after clofibrate treatment (P<0.05). The mRNA of PPARα and LPL were significanlty up-regulated after the clofibrate treatment (P<0.05), but the mRNA of CPT I was no change between the group (P>0.05). These data suggest that clofibrate has the hypolipidaemic effect in the grass carp fed the high-carbohydrate diet and high-fat diet.5. The effects on growth, body composition,biochemical and fat deposition in grass carp fed with vegetable food, broad bean and formulated dietA17-week feeding trial was conducted to evaluate the effects on growth, muscle quality and serum biochemical profile of grass carp (Ctenopharyngodon idellus) fed with the formulated diet (FD), broad bean (BB) or lettuce (L)(Lactuca sativa L.). The FD (Huamei6300) was purchased from a feed company (Conti Huamei Feed Co., Ltd.), BB and L(Lactuca sativa L.) were collected from the farmer’s market (Panyu, Guangdong province). The results showed that the weight gain of fish fed with the FD were significantly higher than the fish fed with L or BB. Fish fed with L had significantly lower lipid content in visceral and muscle than the fish fed with FD or BB. The hardness, springiness, choesiveness, gumminess, chewiness, resiliness of muscle in fish fed with the broad bean were all higher than that of the other two groups. Fish fed with the BB showed a significantly higher ALP activity and CHO content in serum than that with the L. The liver cell was big and loose when fish fed with BB or FD compared with the liver section of grass carp fed with L. The study proved that BB diet could increase the quality of texture, but with a slow growth ratio; FD could bring about a good growth ratio; and L or BB was not a proper feed when each was used alone for grass carp diet.