Physiological and Intestinal Microbiota Responses to the Feeding Stimulant Dimethyl-β-Propiothetin (DMPT) in Aquatic Animals—A Preliminary Study on Pontastacus leptodactylus Fed on a Plant-Based Diet

The replacement of fishmeal with plant protein is a key strategy for sustainable aquaculture, but reduced feed intake and digestive efficiency remain major constraints. This study evaluated the effects of dietary dimethyl-β-propiothetin (DMPT) supplementation on feed intake, digestive function, antioxidant capacity, and intestinal microbiota in narrow-clawed crayfish (Pontastacus leptodactylus) fed an all-plant protein diet. Three isonitrogenous and isolipidic diets were formulated: a plant protein diet (PPD), an animal protein diet (APD), and a PPD supplemented with 0.5% DMPT. After a 4-week feeding trial, results showed that PPD significantly reduced feed intake and digestive enzyme activities compared to APD, whereas DMPT supplementation restored feed intake to a level comparable to APD, maintained growth-related parameters at intermediate levels, and significantly enhanced α-amylase (AMS), lipase (LPS), and trypsin (TPS) activities. Additionally, DMPT markedly improved hepatopancreatic antioxidant capacity, as indicated by increased total antioxidant capacity (T-AOC), glutathione (GSH), catalase (CAT), and superoxide dismutase (SOD) levels, without affecting muscle composition or intestinal morphology. Microbiota analysis revealed that DMPT altered community structure, increased Bacillota abundance, and promoted microbial network stability. Overall, DMPT supplementation effectively mitigates the limitations of plant protein diets and supports the replacement of animal protein in crayfish aquafeeds.