Food Source Variation Shapes Growth and Gut Microbial Ecology: Responses of the Narrow-Clawed Crayfish (Pontastacus leptodactylus) to Contrasting Diets

The narrow-clawed crayfish (Pontastacus leptodactylus) is an economically important aquaculture species, yet its dietary preferences and physiological and gut microbial responses remain poorly understood. Here, we investigated the effects of carrot, shrimp meat, corn, and formulated feed on feeding preference, growth, molting, biochemical traits, digestive enzymes, and gut microbiota. Carrot showed the highest feeding preference, whereas shrimp meat elicited the earliest feeding response. After 60 days, carrot and formulated feed resulted in significantly greater gains in body length and weight than shrimp meat and corn, with no differences in survival. Dietary treatments induced distinct metabolic and digestive responses, with shrimp meat increasing triglycerides, total cholesterol, pepsin, and trypsin; corn increasing glycogen, lactate, and cellulase; and formulated feed producing the highest lipase activity. Carrot feeding markedly reduced gut microbial α-diversity and reshaped community composition, enriching Hafnia-Obesumbacterium, Candidatus Hepatoplasma, and Aeromonas, while reducing Firmicutes, Lactobacillus, and Enterococcus. Predicted phenotypes further indicated an enrichment of facultative anaerobes in carrot-fed crayfish. Overall, carrot and formulated feed promoted growth, whereas carrot exerted a pronounced effect on gut microbial assembly, highlighting the potential of plant-based ingredients as dietary modulators in crayfish aquaculture.