Three groups of juvenile golden pompano, Trachinotus ovatus (54.75 AE 0.25 g), were each fed one of three diets containing different lipid sources: fish oil (FO), soybean oil (SO) and lard oil (LO). Fish were reared in sea cages for 8 weeks, and the fish fed the FO diet had significantly higher specific growth rate (SGR) but lower condition factor (CF) than the other treatments. The fatty acid (FA) composition of whole-body lipids was closely correlated with those in the diets. Although no differences can be found in hepatic fatty acid synthase (fasn) activity, the carnitine palmitoyl transferase 1 (cpt1) activity in fish fed the FO diet was significantly higher compared with other treatments. In addition, the relative gene expression of lipid metabolism-related enzymes, such as cpt1, fas, apolipoprotein B100 (apoB100), delta-6 fatty acyl desaturase (fadsd6) and fatty acid-binding protein 1 (fabp1), was also influenced by the different dietary lipid sources. Serum triglyceride (TG) and glucose content in fish fed the LO and FO diets were significantly higher than those in the SO group. Accordingly, it can be concluded that FO could not be completely replaced by SO or LO in golden pompano diets. The lipid sources of a diet could impose significant influence on body condition factor and hepatic lipid metabolism of golden pompano. K E Y W O R D Sfatty acids, gene expression, lipid metabolism, lipid sources, Trachinotus ovatus | INTRODUCTIONLipids are structural components of cell membranes, a source of energy and essential fatty acids, which are used to promote growth, health and reproduction of fish. In addition, lipids also help to absorb and transport fat-soluble vitamins and are precursors of hormones, vitamin D and eicosanoids, which are biomolecules derived from essential fatty acids that play important roles in the immune system and inflammatory response (Higgs & Dong, 2000;Turchini, Torstensen & Ng, 2009;Wall, Ross, Fitzgerald & Stanton, 2010). Fish oil is considered an important source of lipids for aquatic feed, especially for marine fish, as it can provide high n-3 long-chain polyunsaturated fatty acid (LC-PUFA) content.Marine fish have limited capacity to synthesize, particularly, eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) (Sargent, Bell, McEvoy, Tocher & Estevez, 1999;Glencross, 2009;Tocher, 2010).However, due to the increasing cost and decreasing availability of fish oil, the use of alternative lipid sources such as soybean oil (SO) and lard oil (LO) in marine fish feed tends to increase. ----------------------------------------------------------------------------------------------------------------------------------------------------------------------This is an open access article under the terms of the Creative Commons Attribution-NonCommercial-NoDerivs License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non-commercial and no modifications or adaptations are made. Golden pompano, Trachinotus ovatus is a carnivoro...

Golden pompano (Trachinotus ovatus) is an important aquaculture species in Chinaand broadly cultivated in Asia-Pacific region. Our previous study found that T. ovatus had a better tolerance to the high level of carbohydrate in diet (360 g/kg) compared to Micropterus salmoides. Present study investigated the tolerance mechanism of T. ovatus to high level of dietary carbohydrate (PH-360 g/kg of corn starch) on transcriptome level using Illumina sequencing compared to optimum level of dietary carbohydrate (PM-240 g/kg corn starch). A total of 208,952,492 reads were obtained and assembled into 62,377 unigenes with an average length of 822 bp and a range of 200-16,206 bp. Transcriptome annotation revealed that 27,636 unigenes with a cut-off e-value of 10 −5 were functionally annotated. Specifically, 7,903 unigenes were clustered into 24 functional categories by searching against the COG database, 12,161 unigenes to 84 GO terms, 26,835 unigenes to Nr database and 23,681 unigenes to SWISS-PROT database. In addition, 13,739 unigenes were grouped into 240 KEGG pathways. There are 3,461 differentially expressed genes in PH compared to PM, in which 3,059 unigenes were significantly upregulated and 402 unigenes were significantly downregulated. Twelve key genes related to carbohydrate metabolism were further validated by quantitative real-time RT-PCR, and the results were consistent with those of transcriptome profile. Under high level of dietary carbohydrate (PH-360 g/kg), the results indicate that T. ovatus can adapt to the high level of carbohydrate in diet by enhancing glycolysis with hepatic HK enzyme activity was significantly increased (p > 0.05), reducing gluconeogenesis with the decreased trend of PEPCK enzyme activity and maintaining the homeostasis of carbohydrate metabolism-related hormones and hormone receptor gene expressions. Histopathological examination has shown that liver cavity area was significantly increased (p > 0.05), but no visible nutritional diseases are found in fish. This study provides a valuable understanding of the molecular responses of T. ovatus fed by the high level of dietary carbohydrate (PH-360 g/kg).