As a functional feed additive, grape seed proanthocyanidin extract has received a lot of attention due to its biological activity in the health of aquatic animals, but its high cost limits the application of this feed additive in the diet of many fish species. It is thus urgent to develop a new resource of proanthocyanidin extract. We aimed to investigate the effects of dietary supplementation with peanut skin proanthocyanidins (PSPc) on growth parameters and lipid metabolism of juvenile American eel (Anguilla rostrata). Four hundred and fifty juvenile eels were randomly divided into five groups fed diets with five PSPc supplementation levels. The trial lasted for 8 weeks. Dietary PSPc supplementation significantly improved weight gain and feed utilization, and the best growth performance was found in the group fed with 900 mg/kg PSPc. PSPc supplementation significantly affected the crude protein level of whole fish and serum lipid parameters, and the best lipid-lowering effect was found in the fish fed with 900 mg/kg PSPc. Dietary PSPc supplementation increased lipolytic enzyme activities and decrease lipid synthase levels in the liver. The lipid metabolites affected by 900 mg/kg PSPc in the liver were mainly upregulated phosphatidylethanolamine in autophagy, downregulated ceramides in sphingolipid metabolism, upregulated phosphatidylcholine and phosphatidylethanolamine, downregulated 2-lysophosphatidylcholine in glycerophospholipid metabolism, and upregulated phosphatidylcholine in linoleic acid metabolism. In conclusion, an appropriate level of PSPc might effectively improve growth performance and regulate the lipid metabolism of the juvenile American eel, and 900 mg/kg PSPc is recommended in the diet of this fish species.

Pomelo peel is a main by‐product of pomelo consumption, while most of the by‐products are discarded as wastes with environmental threats. Indeed, it contains many nutrients and bioactive ingredients, which makes it a promising source of aquatic feedstuff. In this study, a 56‐day feeding trial was set out to assess the dietary application of pomelo peel and soybean meal (SBM) (1:4 ratio) fermented compound (PSFC) in large yellow croaker ( Larimichthys crocea ). Results indicated that dietary PSFC improved weight gain rate (WGR) and specific growth rate (SGR), but did not affect feed utilization, body shape parameters and survival rate (SR) of croakers. Moreover, PSFC significantly decreased serum diamine oxidase (DAO) activity and D ‐lactate concentration, increased muscle thickness and villus height, as well as upregulated occludin , claudin-11 , ZO-1 and JAM mRNA levels. The inhibition of proinflammatory IL-1 β and promotion of anti‐inflammatory IL-4/13b and IL-10 expressions were documented in croakers fed with PSFC. Dietary PSFC upregulated intestinal TLR1 , TLR2A , and TLR2B expression, which had significantly positive correlations with improved inflammatory status. Furthermore, PSFC application caused clear alterations in the intestinal microbiota of croakers, which characterized with decreased relative abundances of Verrucomicrobiota and Acidobacteriota and increased relative abundances of unclassified_Muribaculaceae and Akkermansia . Overall, PSFC can significantly improve growth and intestinal health of L. crocea , and showed potential as protein source on L. crocea culture. This work offers a novel insight into the development of fermented protein sources for aquafeeds using pomelo peel and SBM as fermentation ingredients.

The present study was conducted to evaluate whether grape seed proanthocyanidins (GSPs) could alleviate the negative effects of dietary cadmium on growth performance, body composition, activities of digestive enzymes, and antioxidant potential in the intestine of pearl gentian grouper (Epinephelus fuscoguttatus female x Epinephelus lanceolatus male). Two hundred and forty pearl gentian groupers with the initial average body weight of 31.30±0.05 g/fish were randomly divided into four treatment groups with three replicates in each group and 20 fish in each replicate. The four treatment groups were identified as control group (the basal diet), Cd group (the basal diet+300 mg/kg Cd), Cd+GSPs group I (the basal diet+300 mg/kg Cd+400 mg/kg GSPs), and Cd+GSPs group II (the basal diet+300 mg/kg Cd+800 mg/kg GSPs group), respectively. The trial lasted for 42 days. Fish exposed to 300 mg/kg dietary cadmium had lower growth performance, mineral metabolism disorders with lower calcium and phosphorus levels, higher ash level, decreased lipase and protease activities, and antioxidant potential in the intestine. Dietary GSPs supplementation could counteract those negative effects to a certain extent. The alleviation effects of Cd+GSPs group II were better than those of Cd+GSPs group I. Except for calcium and phosphorus levels in whole fish composition, 800 mg/kg dietary GSPs supplementation could not recover the adverse effects caused by Cd stress. These results suggested that GSPs might potentially mediate dietary cadmium toxicity and alleviate the negative effects on pearl gentian grouper.