Effects of dietary γ-aminobutyric acid supplementation on growth, feed intake, and intestinal health of the juvenile Chinese mitten crab (Eriocheir sinensis) fed with high plant protein diets

Due to the global shortage and high price of fish meal, replacing fish meal with plant protein sources is essential for the sustainable development of aquaculture. However, plant protein substitution can exert a series of negative effects on cultured animals, including reduced feed intake and growth performance, and impaired intestinal health. Thus, it is necessary to actively explore nutritional strategies to alleviate these negative impacts. In this study, six experimental diets were formulated: a fish meal control diet containing 35% fish meal; a high plant protein diet containing 15% fish meal and 52% plant protein ingredients, and four high plant protein diets supplemented with GABA at 40, 80, 120, or 160 mg/kg diet. Healthy E. sinensis with initial body weight (0.85 ± 0.05 g) were randomly selected and cultured for 60 days. The results showed that compared with the high plant protein control group, supplementation with 80 and 120 mg/kg GABA in high plant protein diets significantly increased weight gain (WG), specific growth rate (SGR), and feed intake (FI) of E. sinensis (P < 0.05). In addition, GABA supplementation improved the antioxidant capacity of E. sinensis. Specifically, the activities of reduced glutathione (GSH) in the hepatopancreas were significantly elevated, while the malondialdehyde (MDA) contents were significantly decreased in all GABA-supplemented groups (P < 0.05). Supplementation with GABA in high plant protein diets also improved the digestive enzyme capacity of E. sinensis. Specifically, the activities of hepatic lipase (LPS), trypsin (TRY), and intestinal amylase (AMS) were significantly increased (P < 0.05). Furthermore, dietary GABA supplementation in high plant protein diets improved intestinal histomorphology and intestinal microbiota composition, reduced intestinal mucosal permeability, and partially repaired intestinal damage caused by high plant protein. On the other hand, GABA significantly downregulated the expression of appetite-suppressing related genes including Cholecystokinin (CCK), Cholecystokinin receptor (CCKR), AKT serine/threonine kinase (AKT) and Mechanistic target of rapamycin kinase (TOR) (P < 0.05). In summary, dietary supplementation with an appropriate dose of GABA in high plant protein diets may promote the feeding behavior of E. sinensis by downregulating the expression of genes related to appetite suppression, thereby improving its growth performance. Additionally, GABA enhanced the activities of digestive enzymes and antioxidant capacity of juvenile E. sinensis, improved intestinal histological structure and intestinal microbial composition, reduced intestinal mucosal permeability, and thus alleviated the adverse effects caused by high plant protein diets.