In this study, we conducted a 56-d feeding trial to investigate the effects of replacing the fish oil (FO) with palm oil (PO) on the performance, tissue fatty acid (FA) composition, and mRNA levels of genes related to hepatic lipid metabolism in grouper (Epinephelus coioides). Five isolipidic (13% crude lipid) and isonitrogenous (48% CP) diets were formulated by incrementally adding PO to the control diet (25% fish meal and 9% added FO) to replace FO in the control diets. Triplicate groups of 30 groupers (initial weight: 12.6 ± 0.1 g) were fed one of the diets twice daily, to apparent satiety. The replacement of FO with 50% PO revealed maximum growth without affecting the performance and whole-body proximate compositions, and replacing FO with 100% PO revealed a comparable (P > 0.05) growth with that of the control diet, suggesting PO as a suitable alternative to FO. The analysis of FA profiles in the dorsal muscle and liver though reflected the FA profile of the diet, PO substitutions above 50% could compromise (P < 0.05) the FA profile in the liver and flesh of the fish species in comparison with the control diet. Furthermore, the mRNA levels of FAS, G6PD, LPL, PPARΑ, and Δ6FAD genes in the liver had positive linear and/or quadratic responses, but the SCD, HSL, ATGL, FABP, SREBP-1C and ELOVL5 had the opposite trend, with increasing dietary PO inclusion levels, whereas the mRNA level of ACC was not affected by dietary treatments. The optimal level of PO substitution for FO was estimated to be 47.1% of the feed, based on the regression analysis of percent weight gains against dietary PO inclusion levels; however, it might affect the FA profile in the liver and flesh of the fish species, and further study is required to investigate whether the changes in tissue FA composition will affect the welfare and market value over a production cycle of grouper.

Taurine is an indispensable amino acid for many fish species and taurine supplementation is needed when plant-based diets are used as the primary protein source for these species. However, there is limited information available to understand the physiological or metabolic effects of taurine on fish. In this study, ¹H nuclear magnetic resonance (NMR)-based metabolomic analysis was conducted to identify the metabolic profile change in the fish intestine with the aim to assess the effect of dietary taurine supplementation on the physiological and metabolomic variation of fish, and reveal the possible mechanism of taurine’s metabolic effect. Grouper (Epinephelus coioides) were divided into four groups and fed diets containing 0.0%, 0.5%, 1.0%, and 1.5% taurine supplementation for 84 days. After extraction using aqueous and organic solvents, 25 significant taurine-induced metabolic changes were identified. These metabolic changes in grouper intestine were characterized by differences in carbohydrate, amino acid, lipid and nucleotide. The results reflected both the physiological state and growth of the fish, and indicated that taurine supplementation significantly affects the metabolome of fish, improves energy utilization and amino acid uptake, promotes protein, lipid and purine synthesis, and accelerates fish growth.

In the present study, six diets were formulated to contain 24% or 36% protein, and 0, 20%, or 40% starch. The Nile tilapias (Oreochromis niloticus) were fed with the designed diets for 56 days. An overall increasing tendency of percent weight gain, feed efficiency, protein efficiency rate (PER), hepatosomatic index (HSI), and condition factor (CF), whole-body protein and lipid contents, plasma concentrations of triglyceride (TG), total cholesterol (T-CHO) and glucose, liver glycogen contents, liver activities of glucokinase, pyruvate kinase, fatty acid synthetase, lipoprotein lipase (LPL), glucose-6-phosphate dehydrogenase, and malic enzyme with increasing dietary starch level was noted. While the opposite trend was found for feed intake (FI), whole-body moisture and ash contents, liver activities of glucose-6-phosphatase (G6Pase) and phosphoenolpyruvate carboxykinase (PEPCK). Furthermore, all the parameters above were higher in fish fed the 36% vs. 24% protein diets, expect FI, PER, whole-body moisture, liver G6Pase and PEPCK were opposite, and furthermore HSI, whole-body lipid, liver glycogen and LPL were unaffected by dietary protein treatments. The results indicate that Nile tilapia appears to have a more sensitive response to dietary starch level than dietary protein level. Appropriate dietary starch supplementation could help promote the growth of the fish species. Low-dietary protein (24%) allowance may acquire growth comparable to that of Nile tilapia fed 36% protein diets when feed protein is provided only by fish meal with at least 20% starch supplementation.

An 8-week feeding trial was conducted to investigate whether dietary sodium butyrate (SB) administration alleviates growth reduction and enteritis of orange-spotted grouper (Epinephelus coioides) caused by high soybean meal (SBM) feeding. The control diet (FM diet) was formulated to contain 48% protein and 11% fat. Soybean meal was used to replace 60% FM protein in FM diet to prepare a high SBM diet (HSBM diet). Sodium butyrate (SB) at 0.1%, 0.2%, and 0.3% were added to HSBM diets to prepare three diets. Triplicate groups of 30 groupers (initial weight: 33.0 ± 0.3 g) were fed one of the diets twice daily, to apparent satiety. HSBM diets had lowered growth rate and feed efficiency vs FM diets (P &lt;0.05). Growth rate and feed efficiency were improved by dietary SB administration and were in a dose-dependent manner (P &lt;0.05). A similar pattern to the growth rate was observed for plasma LDL-C and gut digestive activity of lipase, trypsin, and protease, but the opposite trend was observed for intestinal contents of D-lactic acid and endotoxin, in response to dietary SB inclusion levels (P &gt;0.05). The muscular thickness in the middle and distal intestines in SB-treated diets were higher than that in HSBM diets (P &lt;0.05). The mRNA levels of intestinal pro-inflammatory cytokines IL-8, IL-1β, IL-12 and TNF-α had a decreasing trend, and the mRNA level of intestinal anti-inflammatory cytokine TGF-β1 had the opposite trend, with increasing SB inclusion levels (P < 0.05). The above results indicate that dietary SB intervention could enhance growth and feed utilization of groupers with SBM-induced enteritis by promoting intestinal digestive enzyme activities, reducing mucosa permeability, maintaining the integrity of intestinal morphology and attenuating the intestinal inflammatory response.