Unveiling the role of dietary protein and lipid levels in modulating digestive and absorptive capacities of a newly cultured fish species Sinilabeo rendahli

Abstract

A 2 × 2 factorial experiment (protein levels, 40 %, and 45 %; lipid levels, 5 %, and 7 %) was conducted to explore the influences of dietary protein and lipid levels on growth performance, digestive and absorptive capacities, and potential signaling molecules of Sinilabeo rendahli (initial weight, 66.19 ± 0.28 g). The formulated diets were named as group 1 (40/5), group 2 (45/5), group 3 (40/7) and group 4 (45/7) (protein/lipid, %), respectively. After an 8-week feeding trial, four diets had no significant effect on the final body weight, percentage of weight gain, and specific growth rate of S. rendahli. However, the group 2 (45/5) showed the lowest feed intake and an increase in feed efficiency of 17.71–34.38 % compared to the other groups. Furthermore, the group with 45 % protein had a higher protein production value compared to the group with 40 % protein, while the highest values for lipid production and ash production were observed in group 2 (45/5). Additionally, protein and lipid digestive and brush border enzyme activities, as well as p-TOR and p-S6k1/S6K1 protein levels were improved in group 2 (45/5), whereas p-4EBP1 was decreased. Meanwhile, the intestinal morphological structure (muscular layer, intestinal folds, and goblet cells) was enhanced in group 2 (45/5). This could be associated with elevated levels of tight junction proteins, including zonula occluden-1, occludin, and claudin-3. Overall, the group 2 (45/5) enhanced the digestive and absorptive capacities through increasing protein and lipid digestive and absorptive enzyme activities, improving intestinal morphology, and higher levels of tight junction proteins in S. rendahli. This suggested that a diet consisting of 45 % protein and 5 % lipid is suitable for S. rendahli.