A moderate dietary potassium diformate (KDF) is favorable for the growth, health status of intestine of juvenile rice field eel, Monopterus albus

To assess the effect of dietary potassium diformate (KDF) on intestine health of juvenile rice field eel, the biochemistry, histomorphology and microbiota properties of intestine were analyzed after an 8-week trial by feeding diets containing different levels of KDF (0.0 %, 0.3 %, 0.6 %, 0.9 %, 1.2 % and 1.5 % in the diets). The results indicated that specific growth rate (SGR) was not affected by the dietary KDF levels ( P > 0.05). Fish fed diet with KDF level at 0.9 % presented a significant improvement on digestive enzymes activity of the foregut and stomach compared with control group (0 % KDF) ( P < 0.05). The activities of intestine SOD, CAT, T-AOC and GSH-PX were significantly improved by the dietary KDF levels ( P < 0.05). Intestine MDA content in the 1.2 % KDF group was significantly lower than that in the 0.3 %, 0.6 %, and 0.9 % treatments ( P < 0.05). The significant elevation of AKP and ACP activities in intestine were observed in KDF supplementation groups ( P < 0.05). The fish in 0.9 % KDF group showed significantly more foregut intestinal folds than that of the other treatments ( P < 0.05). Inclusion of KDF in diets significantly increased the number of goblet cells in both the foregut and hindgut, and achieved the highest value at 0.9 % KDF group ( P < 0.05). No significant effect was found on the α-diversity indices of gut ( P > 0.05). At the phylum level, the intestinal microbiota was predominantly comprised of Proteobacteria, Firmicutes, Verrucomicrobiota, Fusobacteriota, Actinobacteriota, and Bacteroidota. The study revealed that an appropriate supplementation of KDF in diet is beneficial for the growth and intestinal health status of rice field eel by improving digestive enzymes activity, intestinal morphology and antioxidant capacity. The optimum supplementation level of KDF in juvenile rice field eel diet is determined at 0.88 g/kg based on SGR. • Dietary KDF supplementation can lower the gastric and intestinal pH of juvenile rice field eel. • KDF is beneficial for improving the growth, antioxidant capacity and intestine health of rice field eel. • The optimum supplementation level of KDF in rice field eel diet is 0.88%.