Effects of carbohydrate sources on the physical quality of extrudate and their subsequent effects on feed intake, digestion and gut microbiota in spotted seabass (Lateolabrax maculatus)

This study investigated the impact of carbohydrate sources on the physical quality of extruded pellets and their subsequent effects on feed intake, digestion, gut microbiota, and fermentation in spotted seabass (<i>Lateolabrax maculatus</i>). Three diets with different carbohydrate sources (cassava flour [CF], wheat flour [WF], and broken rice flour [RF]) were produced, each with a 20% inclusion level, under identical extrusion conditions. The moisture content of the mash entering the extruder was 24.5% and the die temperature was set at 145 °C. After extrusion, pellet physical quality (e.g., floatability, hardness, and water stability) and microstructure were evaluated. A total of 270 fish (initial body weight 15.7 ± 0.02 g) were randomly stocked into nine tanks (30 fish per tank) and fed one of the three diets to apparent satiation. Each diet was tested in triplicate. Feed intake, nutrient digestibility, and fish performance were evaluated over an 8-week experimental period. At the end of the experiment, chyme from the stomach and intestine was collected at 2, 6, 12, and 24 h postprandial. Stomach relative water flux, nutrient digestibility, gastrointestinal emptying, gut microbiota, and volatile fatty acids (VFA) were determined. Extrusion reduced the amylose and resistant starch content in all diets. The RF pellets were slow sinking and had a more compact structure characterized by lower pore area and porosity compared to the floating pellets of the WF and CF pellets (<i>P</i> < 0.001). The compact structure of RF pellets was negatively correlated with the digestibility of protein (<i>P</i> < 0.001) and dry matter (<i>P</i> = 0.001). Different carbohydrate sources influenced the digestibility of all nutrients (<i>P</i> < 0.05). The WF diet exhibited the highest protein (<i>P</i> < 0.001) and fat digestibility (<i>P</i> = 0.014), but the lowest starch digestibility (<i>P</i> = 0.003). Carbohydrate sources did not affect the overall richness and diversity of gut microbiota (<i>P</i> > 0.05). However, the WF diet led to a higher abundance of phylum Firmicutes (<i>P</i> = 0.033) and higher total VFAs (<i>P</i> = 0.030) in fish than the other diets. Gastrointestinal emptying, feed intake, and growth were unaffected by carbohydrate sources (<i>P</i> > 0.05); however, the WF diet resulted in a higher feed conversion ratio and protein efficiency ratio than the other diets (<i>P</i> < 0.05). In conclusion, different carbohydrate sources can influence pellet physical quality and digestion, but not feed intake or gut microbiota in spotted seabass.