Evaluation of a hepatic biomarker of nutritional imbalance in juvenile red drum(Sciaenops ocellatus)fed 60%soybean meal-based diets using NMR-based metabolomics

A 12-week feeding trial with juvenile red drum(Sciaenops ocellatus) fed high-soybean meal(SBM) diets was conducted to investigate a putative biomarker of nutritional imbalance, N-formimino-L-glutamate(FIGLU). Three fishmeal-free, 60% SBM pelleted diets(named B12, Fol, and Met, respectively) were tested to evaluate the effects on growth performance and tissue metabolite profiles of supplementation of vitamin B12(0.012 mg/kg), folate(10 mg/kg), methionine(1 g/kg) respectively, above basal supplementation levels. A fourth SBM-based diet(named B12/Fol/Met) was formulated with a combination of B12, folate, and methionine to attain the above-mentioned target concentrations. A fifth 60% SBM diet(named FWS) with methionine supplementation(1 g/kg above basal supplementation levels), enriched with taurine, lysine and threonine as well as minerals, was also tested. This diet contained formulation targets and additives which have allowed for replacing fishmeal with plant proteins in rainbow trout feeds. Control diets included a fishmeal-based diet(named FM), an unsupplemented basal 60% SBM diet(named SBM60), and a “natural” diet(named N) made up of equal parts of fish(cigar minnows), squid and shrimp as a positive reference for growth performance. Formulated feeds contained approximately 37% total crude protein, approximately 14% total crude lipid and were energetically balanced. Standard growth performance metrics were measured, and tissues(liver, muscle) were collected at week 12 to evaluate diet-induced metabolic changes using nuclear magnetic resonance(NMR)-based metabolomics.Our results show that the FWS diet outperformed all other SBM diets and the FM diet under all performance metrics(P<0.05). FIGLU was not detected in fish fed the N diet but was detected in those fed the SBM diets and the FM diet. Fish fed the FWS diet and the Met diet showed lower hepatic levels of FIGLU compared with the other SBM-based diets(P<0.05), suggesting that among the different supplementation regimes, methionine supplementation was associated with lower FIGLU levels. The FWS diet produced tissue metabolite profiles that were more similar to those of fish fed the N diet. Based on our results, the FWS diet constitutes a promising SBM-based alternative diet to fishmeal for red drum.

Chronic exposure to high-density polyethylene microplastic through feeding alters the nutrient metabolism of juvenile yellow perch (Perca flavescens)

Microplastics are emergent contaminants threatening aquatic organisms including aquacultured fish.This study investigated the effects of high-density polyethylene(HDPE,100 to 125 mm)on yellow perch(Perca flavescens)based on integrative evaluation including growth performance,nutritional status,nutrient metabolism,fish health,and gut microbial community.Five test diets(0,1,2,4,or 8 g HDPE/100 g diet)containing 41%protein and 10.5%lipid were fed to juvenile perch(average body weight,25.9±0.2 g;n=15)at a feeding rate of 1.5%to 2.0%body weight daily.The feeding trial was conducted in a flow-through water system for 9 wk with 3 tanks per treatment and 15 yellow perch per tank.No mortality or HDPE accumulation in the fish was found in any treatments.Weight gain and condition factor of fish were not significantly impacted by HDPE(P>0.05).Compared to the control group,fish fed the 8%HDPE diet had significantly decreased levels of protein and ash(P<0.05).In response to the increasing levels of HDPE exposure,the hepatosomatic index value,hepatocyte size,and liver glycogen level were increased,but lipid content was reduced in the liver tissues.Compared to the control treatment,fish fed the 8%HDPE diet had significant accumulations of total bile acids and different metabolism pathways such as bile acid biosynthesis,pyruvate metabolism,and carnitine synthesis.Significant enterocyte necrosis was documented in the foregut of fish fed the 2%or 8%HDPE diet;and significant cell sloughing was observed in the midgut and hindgut of fish fed the 8%HDPE diet.Fish fed the 2%HDPE diet harbored different microbiota communities compared to the control fish.This study demonstrates that HDPE ranging from 100 to 125 mm in feed can be evacuated by yellow perch with no impact on growth.However,dietary exposure to HDPE decreased whole fish nutrition quality,altered nutrient metabolism and the intestinal histopathology as well as microbiota community of yellow perch.The results indicate that extended exposure may pose a risk to fish health and jeopardize the nutrition quality of aquacultured end product.This hypothesis remains to be investigated further.