Effects of Dietary KDF on Growth Performance, Blood Biochemistry, Hepatic Health and Disease Resistance in Juvenile Ricefield Eel

KDF (potassium diformate) has been recognized as a highly promising additive due to its beneficial effects on growth and immunity improvement. In order to expand the application of KDF in the aquatic farming practice, the effects of KDF on ricefield eels were thoroughly evaluated. In the present study, the growth performance, blood biochemistry, hepatic health and disease resistance were assessed in the juvenile ricefield eels fed diets supplemented with 0 (D0), 3 (D1), 6 (D2), 9 (D3), 12 (D4) and 15 (D5) g/kg KDF. After 8 weeks feeding, fish weight gain rate (WGR) was improved by KDF addition, and the estimated optimum dietary KDF was determined at 8.91 g/kg according to the regression analysis between dietary KDF level and WGR. Fish condition factor (CF) was increased by dietary KDF supplementation compared to the control (D0). The VSI of fish decreased significantly and then kept stable when the dietary KDF level was above 9 g/kg (p < 0.05). The supplementation of KDF in diet had no significant effect on the moisture, crude ash, and crude protein contents of the whole fish (p > 0.05), while the crude lipid content in the D4 group was significantly lower than that in the control (p < 0.05). Compared to the control group, the inclusion of 9 g/kg KDF (D3) in the diet significantly decreased serum aspartate aminotransferase (AST) and alanine aminotransferase (ALT) (p < 0.05). Liver catalase (CAT) activity increased significantly with increasing the level of KDF in diet, but it remained stable at KDF levels at and above 9 g/kg (D3) (p < 0.05). The significant improvement of glutathione peroxidase (GSH-Px) activity and total antioxidant capacity (T-AOC) were found in the D1 and D4 groups, respectively (p < 0.05). Liver malondialdehyde (MDA) content showed a non-monotonic pattern across KDF levels, and the addition of KDF in diet did not significantly alter MDA content compared to the control (p > 0.05). Fish in the D4 group showed the lowest liver malondialdehyde (MDA) content. Serum ALP activity was markedly elevated in the D3 group compared with the control (p < 0.05). Supplementation of KDF in diets enhanced hepatic ALP and ACP activities, which differed significantly from the control in the D3 and D4 groups, respectively (p < 0.05). The histological results indicated that while no significant alteration of liver cell structure was observed, fish liver showed a lower number and size of lipid droplets with the KDF level increasing, and the hepatic sinusoids appeared more prominent in the high KDF group (D5). The Aeromonas hydrophila challenge test demonstrated that the addition of 9 g/kg KDF (D3) in fish diet significantly increased the survival rate of juvenile ricefield eel (p < 0.05). In summary, dietary supplementation with KDF significantly enhanced growth performance, improved several biomarkers associated hepatic health, and strengthened pathogen resistance in juvenile ricefield eels.