Effects Of N-3HUFA On Growth Performance, Lipid Metabolism, And Health Status In Grass Carp,Ctenopharyngodon Idellus

In order to explore the effects of n-3highly unsaturated fatty acids (n-3HUFA) on growth performance, health status, and the lipid metabolism in grass carp, two isonitrogenous and isolipidic diets were formulated with either lard oil or fish oil as the main lipid source. After a95-day feeding trial, the growth performance, biological and serum biochemical parameters, tissue fatty acid profile, antioxidation status, and expression of lipid-metabolism-and immune-related genes in grass carp were detected. Moreover, transcriptome of Ctenopharyngodon idellus was analyzed by the Next-Generation DNA Sequencing Technique (RNA-Seq). The main results were as follows:(1)A95-day feeding trial was conducted to determine the effects of n-3HUFA on the biological and serum biochemical parameters, tissue fatty acid profile, antioxidation status, and expression of lipid-metabolism-and immune-related genes in grass carp (Ctenopharyngodon idellus). Two isonitrogenous and isolipidic diets were formulated with either lard oil (LO) or fish oil (FO) as the main lipid source. Each diet was randomly fed to triplicate tanks of fish (12fish/tank, initial weight40.3g). The two groups were named LO group (control group) and FO group (n-3HUFA group), respectively. The results showed that there was no significant difference in weight gain, specific growth rate, feed conversion ratio, or condition factor between the two groups (P>0.05). However, the intraperitoneal fat (IPF) ratio and relative intestine length (RIL) were significantly lower (P<0.05) and the hepatosomatic index (HSI) and spleen/body weight ratio were significantly higher (P<0.05) in the FO group than in the LO group. Results of serum biochemical parameters from3fish each tank showed that the levels of alkaline phosphatase (ALP) and low density lipoprotein-cholesterol (LDL-C) of FO group were significantly lower (P<0.05), whereas the levels of alanine aminot ransferase (ALT), aspartate aminot ransferase (AST), and glucose (GLU) were significantly higher (P<0.05) than those of LO group. The fatty acid composition of muscle, hepatopancreas, and IPF was influenced by the fatty acid composition of the respective diets. The concentration of n-3HUFA in those tissues was significantly higher in the FO group than in the LO group (P<0.05). The serum total superoxide dismutase (T-SOD) activity was significantly higher (P<0.05) in the FO group, consistent with the serum malondialdehyde (MDA) content. The results of quantitative real-time PCR (qRT-PCR) assays indicate that the gene expression of IPF fatty acid synthase (FAS), acetyl-CoA carboxylase (ACC), sterol regulatory element-binding protein (SREBP-1), and peroxisome proliferator-activated receptor y (PPARy) was significantly lower (P<0.05) and that of peroxisome proliferator-activated receptor a (PPARa) was significantly higher (P<0.05) in the FO group than in the LO group. Similar expression trends were found in the hepatopancreas, except for PPARy. In addition, the expression of Liver X Receptor a (LXRa) was significantly lower (P<0.05) in FO group than that of LO group. The expression of two immune-function-related genes, toll-like receptor22(TLR22) and myeloid differentiation factor88(MyD88), in the spleen and kidney were significantly higher (P<0.05) in the FO group than in the LO group.(2) To obtain an overview of the grass carp gene expression profile at hepatopancreas, two total RNA samples isolated from the two materials (A1for LO group and B1for FO group,6fish/group). Then the cDNA samples were subjected to sequence by using the Illumina Cluster Station and Illumina Genome Analyzer. Up to2,201Mb data (percentage of GC:48.7%) for A1and2257Mb data (percentage of GC:48.65%) for B1were obtained. Approximately37,341and43,085transcripts were obtained for hepatopancreas A1and B1, respectively. The number of length of>1000bp was5,103for Al and5,934for B1. Approximately27,699and30,494unigenes were obtained for hepatopancreas Al and B1, respectively, of which2,673with length of>1000bp for A1and3,028for B1. From the unigene base we have obtained total of45,098unigenes, and about4,157(9.217%) were>1000bp long. Tested by IDEG6software,232differentially expressed genes were found. Differentially expressed genes and their functions were predicted by GO and COG analysis.Conclude:It is suggested that n-3HUFA could inhibit lipid accumulation in grass carp by affecting the expression of lipid-metabolism-related transcription factors and genes. It was demonstrated that n-3HUFA may play important role in initiation of innate immune responses in grass carp. Meanwhile, the negative effect of n-3HUFA should be put into consideration. Through the analysis of hepatopancreas transcriptome,232differentially expressed genes were found. However, the effects of n-3HUFA on the expression of genes related to lipid metabolism and inflammation need further confirmation.