Dietary Malondialdehyde Damage to the Growth Performance and Digestive Function of Hybrid Grouper (Epinephelus fuscoguttatus♀ × E. lanceolatu♂).

Malondialdehyde (MDA) is the dominant component of lipid peroxidation products. Improper storage and transportation can elevate the lipid deterioration MDA content of diets to values that are unsafe for aquatic animals and even hazardous to human health. The study aimed to investigate the effect of dietary MDA on growth performance and digestive function of hybrid grouper (Epinephelus fuscoguttatus♀ × E. lanceolatu♂). Six isoproteic and isolipidic diets were formulated to contain 0.03, 1.11, 2.21, 4.43, 8.86 and 17.72 mg/kg MDA, respectively. The study shows that the increased dietary MDA content linearly reduced the growth rate, feed utilization, body index and body lipid content of hybrid grouper, while the low dose of dietary MDA (≤2.21 mg/kg) created no difference. Similarly, dietary MDA inclusion linearly depressed the activities of intestinal digestive and absorptive enzymes as well as antioxidant enzymes, enhanced the serum diamine oxidase activity, endotoxin level and intestinal MDA content. A high dose of MDA (≥4.43 mg/kg) generally impaired the gastric and intestinal mucosa, up-regulated the relative expression of Kelch-like ECH-associated protein 1 but down-regulated the relative expression of nuclear factor erythroid 2-related factor 2 in hindgut. In conclusion, the effect of MDA on hybrid grouper showed a dose-dependent effect in this study. A low dose of dietary MDA had limited effects on growth performance and intestinal health of hybrid grouper, while a high concentration damaged the gastrointestinal structure, depressed the intestinal digestive and antioxidant functions, and thereby impaired the growth and health of hybrid grouper.

Effects of Dietary Lysine Level on Growth Performance and Protein Metabolism in Juvenile Leopard Coral Grouper (Plectropomus leopardus).

An 8-week feeding trial was conducted to evaluate the effects of dietary lysine level on growth performance and protein metabolism of juvenile leopard coral grouper (Plectropomus leopardus) and thereby obtained the optimal dietary lysine requirement of P. leopardus. Six isoproteic and isolipidic experimental diets were formulated to contain 1.10%, 1.69%, 2.30%, 3.08%, 3.56%, and 4.36% lysine of diets, respectively. Each diet was assigned at random to triplicate groups of 25 juveniles (initial mean weight is 10.57 g) per tank in a flow-through mariculture system maintained at 27-30°C. Dietary inclusion of 2.30-3.08% lysine improved the weight gain rate (WGR) and specific growth rate and decreased the feed conversion ratio (FCR) of juveniles (P < 0.05). The intestinal digestive enzyme (trypsin, amylase, and lipase) activities were overall enhanced by dietary inclusion of 3.08-3.56% lysine (P < 0.05). The mammalian target of rapamycin (mTOR) signaling pathway was activated in fish fed diets with 1.69-2.30% lysine by upregulating the relative expression levels of hepatic TOR and S6K1 (p70 ribosomal protein S6 kinase 1) but downregulating the relative expression level of hepatic 4E-BP2 (eIF4E-binding protein 2). Conversely, the amino acid response signaling pathway was inhibited in fish fed diet with 2.30% lysine by downregulating the relative expression levels of hepatic GCN2 (general control nondepressible 2), ATF3 (activating transcription factor 3), ATF4a (activating transcription factor 4a), and ATF4b (activating transcription factor 4b). Additionally, dietary 1.69-3.08% lysine enhanced the plasma total protein level and hepatic lysine α-ketoglutarate reductase activity but depressed the blood urea nitrogen level and hepatic adenosine monophosphate deaminase activity (P < 0.05). Moreover, dietary 3.08% lysine increased the contents of whole-body crude protein and total amino acids, while 1.69%-4.36% lysine depressed the whole-body lipid content (P < 0.05). These results indicated that optimal dietary lysine increased the digestive enzyme activities, promoted protein synthesis but depressed protein degradation, and thereby improved the growth performance of P. leopardus. Based on the second-order polynomial model, the optimal lysine requirement of juvenile P. leopardus for WGR, FCR, and lysine deposition was 2.60%-2.97% of diets (4.91%-5.60% of dietary protein).

High Dietary Histamine Induces Digestive Tract Oxidative Damage in Juvenile Striped Catfish (Pangasianodon hypophthalmus).

A 56-day feeding trial investigated the effects of dietary histamine on the antioxidant capacity, gastric and intestinal barrier functions, and growth performance of striped catfish (Pangasianodon hypophthalmus). Seven isonitrogenous (34.0% crude protein) and isolipidic (10.5% crude lipid) diets were formulated with supplemental 0, 15, 30, 60, 120, 240, and 480 mg/kg of histamine, named H0, H15, H30, H60, H120, H240, and H480 group, respectively. Results showed that the weight gain rate, specific growth rate, relative intestinal length in the H240 and H480 groups, and the condition factors in the H480 group were significantly lower than those in the H0 group. Intestinal total antioxidant capacity, peroxidase, catalase, superoxide dismutase, glutathione peroxidase, and glutathione reductase activities in the H480 group were significantly lower than those in the H0 group, whereas intestinal malondialdehyde content exhibited the opposite trend. Intestinal complement 3, complement 4, immunoglobulin M, and Recombinant Mucin 2 in the H480 group were significantly lower than those in the H0 group, in contrast to intestinal lipopolysaccharide content. Intestinal IL-10 gene expression in the H480 group was significantly lower than that in the H0 group, whereas the TNF-α, IL-1, IL-6, and IL-8 gene expression exhibited opposite results. Scanning and transmission electron microscopic observation of the gastrointestinal tract revealed severe damage to the gastric mucosa and intestinal epithelium in the H480 group. The abundance of Treponema in the histamine groups was significantly higher than that in the H0 group. These results indicated that high dietary histamine decreases intestinal immunity and antioxidant capacity, inducing digestive tract oxidative damage and ultimately decreasing the growth of striped catfish.

Different Types of Non-Starch Polysaccharides Alter the Growth, Intestinal Flora and Serum Metabolite Profile of Grass Carp, Ctenopharyngodon idella.

Dietary non-starch polysaccharides (NSPs) broadly influence fish intestinal flora and physiological metabolism, but limited information is available on grass carp (Ctenopharyngodon idella). This study investigated the effects of different types of NSPs on the growth, nutrient metabolism status, gut microbiota, and serum metabolome of grass carp. Fish were fed with diets containing 4.4% insoluble NSPs (INSP), 9.24% soluble NSPs (SNSP), 13.64% NSPs (4.4% INSP + 9.24% SNSP, NSP) and non NSPs (FM), respectively, for 9 weeks. Results showed that dietary SNSP decreased protein efficiency ratio and serum protein content, but increased feed coefficient ratio, feed intake, plasma blood urea nitrogen content, and plasma aspartate aminotransferase activity (AST); conversely, dietary INSP decreased plasma AST activity. Dietary INSP and SNSP increased serum free cholesterol content. Dietary NSPs altered the abundance of dominant bacteria and serum metabolite profiles. The differential metabolites between groups were significantly enriched in amino acid synthesis and metabolic pathways. In conclusion, dietary INSP exhibited a growth-promoting effect compared to SNSP. Dietary INSP is beneficial for improving nutrient metabolism and intestinal health. Moreover, dietary NSPs may regulate the physiological metabolism and feeding behavior of grass carp by altering amino acid synthesis and metabolism.