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A six-week feeding trial was conducted to investigate the effects of dietary starch levels on growth performance, glucose and lipid metabolism and insulin signaling pathway of juvenile Scylla paramamosain. Three isonitrogenous (41.51% ± 0.31%) and isolipidic (8.68% ± 0.53%) experimental diets were formulated to contain 10%, 20% and 30% starch levels, respectively. A total 96 crabs were divided into 3 treatment groups. There were 4 replicates per treatment group and 8 crabs per replicate (initial weight 5.12 ± 0.05 g). The crabs fed the diet with 20% starch showed the best growth performance, with higher weight gain rate (WGR), specific growth rate (SGR), protein efficiency ratio (PER), and feed efficiency (FE) compared to the other diets. Increasing starch levels in the diet resulted in higher levels of glycogen and lipid in the muscles and hepatopancreas. The levels of glucose (GLU), triglyceride (TG), and free fatty acid (FFA) displayed a significant increase in both hemolymph and hepatopancreas with the escalating dietary starch concentrations. In contrast, as the dietary starch levels increased, the concentrations of crustacean hyperglycemic hormone (CHH) and insulin-like peptides (ILPs) in hemolymph and hepatopancreas demonstrated a notable decline. The glycolysis and pentose phosphorylation pathways were significantly promoted, while the gluconeogenic pathway was significantly inhibited, with dietary starch levels increasing from 10% to 30%. Additionally, increasing dietary starch levels led to a significant down-regulation of genes related to the lipid synthesis, lipolysis and insulin signaling pathway. Histological results showed that hepatopancreas fat accumulation increased with the increase of dietary starch level. Overall, the findings of this study suggest that adding 20% starch to the diet can promote growth and improve nutrient utilization. In addition, the level of dietary starch had significant effects on the glucose and lipid metabolism and insulin signaling pathway of mud crabs, thus affecting the deposition of lipid reserves in hepatopancreas.

Cadmium (Cd) is a major pollutant in water, and long-term Cd exposure seriously threatens aquatic organisms. This study evaluated the effects of dietary Cd on growth performance, tissue Cd accumulation, oxidative stress, endoplasmic reticulum (ER) stress, inflammation, apoptosis, and anti-stress response in juvenile black seabream (Acanthopagrus schlegelii). Six experimental diets containing different concentration of Cd were formulated: 0.02 (Control, Cd0.02), 1.60 (Cd1.60), 24.29 (Cd24.29), 49.04 (Cd49.04), 117.26 (Cd 117.26), and 289.65 (Cd289.65) mg/kg. A feeding experiment was performed on 540 juvenile black seabreams (initial weight, 1.42 ± 0.01 g), which were conducted for ten weeks. The findings revealed that Cd in the diet lowered weight gain (WG) and specific growth rate (SGR), but had no effect on survival. Dramatically positive linear trends were found between increasing dietary Cd contents and tissue Cd accumulation, including liver, kidney, and muscle. Dietary Cd exposure increased malondialdehyde (MDA) production in both serum and liver, hence, caused oxidative stress. The endoplasmic reticulum (ER) stress-related genes, including grp78, atf6, and xbp1, were markedly increased with increased dietary Cd levels, showing ER stress was triggered. Likewise, transcriptional expression levels of genes related to anti-stress response mt2, hsp70, and hsp90 were linearly up-regulated with increased dietary Cd contents. Regarding apoptosis, the transcriptional expression levels of pro-apoptosis genes caspase7, caspase9, and bax and anti-apoptosis gene bcl-2 were all significantly promoted with the increasing dietary Cd levels. Similar patterns were found for gene expression levels linked to inflammatory response, as the dietary Cd contents increased, nuclear transcription factor nf-κb, pro-inflammatory cytokines tnfα and il-1β, and anti-inflammatory il-10 and tgfβ were dramatically elevated. In conclusion, dietary Cd supplementation suppressed growth performance, increased Cd deposition in tissues, induced oxidative stress, ER stress, apoptosis, and inflammation. In contrast, black seabream juveniles also showed substantial tolerance for dietary Cd exposure by promoting anti-stress ability.

Three isonitrogenous diets (41% crude protein) with 4.87%, 10.75% and 16.10% lipid were designed to evaluate the effects of dietary lipid levels growth, antioxidant capacity, expression levels of genes related to lipid and glucose metabolism of juvenile Scylla paramamosain. Each diet was fed to four replicates of 32 crabs with initial weight 5.10 ± 0.05 g for 6 weeks. The results indicated that crabs fed diet with 10.75% lipid exhibited significantly higher percent weight gain (PWG) and specific growth rate (SGR) than those fed diet with 4.87% lipid (P

As a functional fatty acid, Arachidonic acid (ARA) plays an important role in immunity due to its metabolites in mammals, which have been extensively studied in mammals. However, studies on the function of metabolites produced by dietary ARA in aquatic animals are not comprehensive and in-depth. Hence, an eight-week feeding trial was conducted to evaluated the regulatory effects of dietary ARA and its metabolites-eicosanoids on inflammation, oxidative stress and apoptosis in the liver of Acanthopagrus schlegelii with an initial weight of 0.99 ± 0.10 g. Six isonitrogenous and isolipidic (41% protein, 14% lipid) diets were formulated with gradient levels of ARA: 0% (ARA0.10), 0.5% (ARA0.59), 1.0% (ARA1.04), 1.5% (ARA1.42), 2.0% (ARA1.94), 2.5% (ARA2.42), respectively, and palmitic acid was used to regulate lipid levels. Results showed that the key enzyme contents of ARA metabolic pathway such as phospholipase A2 (PLA2), cyclooxygenase-2 (COX-2), lipoxygenase (LOX) cytochrome P450 (CYP450), prostaglandin E2 (PGE2), leukotriene C4 (LTC4) and 20-hydroxyeicosatetraenoic acid (20-HETE) in the liver were increased with dietary ARA levels increased. High levels of dietary ARA (1.94% and 2.42%) activated the gene expression levels of nuclear factor kappa B (nf-κb), which were confirmed by the results of immunofluorescence assay. Likewise, the expression levels of pro-inflammatory cytokines (tnf-α and il-1β) were up-regulated by ARA1.94 and ARA2.42 groups. Fish fed with excess ARA level has significantly low antioxidant capacity by decreasing the activity of related antioxidant parameters and down-regulating the expression level of related genes. The pro-apoptotic related genes (bax and caspase 7/9) were markedly up-regulated as dietary ARA levels increased from 1.04% to 2.42%. Collectively, excess dietary ARA levels (1.92% and 2.42%) produced excess eicosanoids, triggering inflammation via activating NF-κB expression and promoting its nuclear translocation, resulting in oxidative stress by reducing antioxidant parameters (SOD, GSH and GPX), inducing cell apoptosis through up-regulating pro-apoptotic gene expression levels.

Vegetable oil (VO) is increasingly replacing fish oil (FO) in the commercial diet of crustaceans, partly due to a global shortage of FO. But little is known about how different amounts of substitution affect the health and metabolism of crustaceans. A six-week feeding trial was conducted to evaluated the effects of different replacement levels of FO with linseed oil (LO) on growth performance, antioxidant and digestive capacity and fatty acid metabolism in swimming crab, Portunus trituberculatus. Five isonitrogenous and isolipidic diets (480 g kg−1 protein and 120 g kg−1 lipid) were formulated to contain graded levels of LO, and FO was replaced with LO at 0%, 25%, 50%, 75% and 100%, respectively. The results showed that 50% of FO could be replaced by LO without affecting the growth performance and feed utilization for juvenile swimming crab. In hemolymph, 100% dietary replacement of FO with LO, the activities of alanine aminotransferase (ALT) and aspartate transaminase (AST) exhibited significantly higher than those fed the other diets, the concentrations of triacylglycerol (TAG), total cholesterol (T-CHO) and high-density lipoprotein cholesterol (HDL-C) significantly increased with increase of dietary replacement of FO with LO, which may lead to hyperlipidemia in swimming crabs. The number of R cells and their lipid droplets in hepatopancreas gradually increased with increase of replacement of FO with LO, the results confirmed the occurrence of lipid accumulation in the hepatopancreas. The activities of glutathione (GSH), and glutathione peroxidase (GPX) in hepatopancreas significantly decreased with increase of replacement of FO with LO, and crabs fed diet with 50% replacement of FO with LO had higher activities of trypsin and lipase (LPS) than those fed the other diets. Long-chain polyunsaturated fatty acids (LC-PUFA), n-3/n-6 PUFA in hepatopancreas and muscle significantly decreased with the increase of substitution level of FO with LO. Moreover, the expression of genes related to LC-PUFA synthesis as well as fatty acid β-oxidation, such as elongase 4 (elovl4), hepatocyte nuclear factor 4-α (hnf4α), retinoid X receptor (rxr), carnitine palmitoyltransferase 2 (cpt2) and acyl-CoA oxidase (acox2), were down-regulated with increase of dietary replacement of FO with LO. In conclusion, it is suggested that the optimal substitution ratio of LO for FO should be less than 50% in the diet of Portunus trituberculatus.

An eight-week feeding trial was conducted to investigate the effects of dietary lipid sources on growth performance, fatty acids composition in tissue and expression of genes related to lipid metabolism in juvenile largemouth bass (Micropterus salmoides). Four experimental diets were formulated to contain 6% coconut oil (CO), rapeseed oil (RO), linseed oil (LO) and fish oil (FO), respectively. Each diet was fed to triplicate groups of juvenile for 8 weeks. The results indicated that final body weight (FBW), percent weight gain (PWG), specific growth rate (SGR), feed efficiency (FE), survival, hepatopancreas index (HSI), viscerosomatic index (VSI) and intraperitoneal fat ratio (IPF) were not significantly influenced by dietary different lipid sources (P＞0.05). Moreover, proximate composition in whole body, dorsal muscle and liver were also not significantly affected by dietary different lipid sources (P ＞0.05). Fish fed with FO diet was significantly higher MDA concentration in hepatic and serum than those fed with CO, RO and LO diets (P

Since discovery, glucagon biology has remained enigmatic. Studies have shown that glucagon may have physiological effects beyond glucose regulation by binding to its receptor (Gcgr). The potential roles of glucagon and its receptor in the crosstalk between glucose metabolism and immune function of fish remain to be investigated. In the present study, we sequenced and characterized gcgra and gcgrb in grass carp. Phylogenetic analysis showed that they were highly homologous with their counterparts in fish. The gcgra and gcgrb mRNAs were ubiquitously expressed in all the tissues examined. The gcgra mRNA was highly expressed in the liver and gcgrb was mainly expressed in the liver and brain regions of grass carp. Furthermore, the results of oral glucose tolerance test (OGTT) showed that the expression levels of the two receptors were significantly increased at 12 h after treatment. In the hepatocytes, insulin inhibited gcgra and gcgrb mRNA expressions at 3−12 h and 6−12 h, respectively. While glucagon promoted their expressions at 3−12 h and 3 h, respectively. Intraperitoneal injection of lipopolysaccharide (LPS) increased hepatic gcgra mRNA level at 6 h post treatment, and up-regulated gcgrb mRNA abundance in the liver at 24 h. In response to polyinosinic polycytidylic acid [poly (I:C)] stimuli, however, gcgra and gcgrb mRNA levels were decreased. These results suggested that glucagon receptors were affected by bacterial-like and virus-like infection beyond their roles in the glucose metabolism of grass carp.