Pomelo Peel and Soybean Meal Fermented Compound as Feedstuff for Large Yellow Croaker (Larimichthys crocea): A Study...

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-1β 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.