DIETARY EXTRUSION TEMPERATURE ON GROWTH PERFORMANCE, NUTRIENT DIGESTIBILITY, WASTE DISCHARGE, AND GASTROINTESTINAL MICROBIOTA OF LARGEMOUTH BASS (MICROPTERUSSALMOIDES)

This study investigated the effects of dietary extrusion temperature on growth performance, nutrient digestibility, waste discharge, and gastrointestinal microbiota of largemouth bass (<italic>Micropterus salmoides</italic>). Fish were fed diets containing 48% protein and 9% fat, extruded at two three-stage heating programs (D1: 100℃, 120℃, 120℃; D2: 100℃, 120℃, 140℃), in an indoor recirculating system for 63d. Compared to the D1 group, the D2 group exhibited significantly higher final body weight, weight gain rate, and specific growth rate, along with a lower feed conversion ratio (<italic>P</italic>&lt;0.05). The D2 group also showed a significantly reduced hepatopancreas index but an increased viscerosomatic index (<italic>P</italic>&lt;0.05). Nutrient retention efficiency of carbon and phosphorus and apparent protein digestibility were significantly improved in the D2 group (<italic>P</italic>&lt;0.05), though apparent phosphorus digestibility did not differ between the two groups (<italic>P</italic>&gt;0.05). While whole fish and fecal carbon, nitrogen, and phosphorus contents remained similar between groups (<italic>P</italic>&gt;0.05), the D2 group showed significantly lower waste outputs (<italic>P</italic>&lt;0.05). Distinct microbial communities were observed between the stomach and intestine (<italic>P</italic>&lt;0.05), but extrusion temperature had no significant effect on alpha diversity of the digestive tract and the community structure (<italic>P</italic>&gt;0.05). These findings suggest that moderately increasing extrusion temperature enhances growth performance and nutrient utilization in largemouth bass while maintaining microbial community stability and reducing aquaculture waste output.