REPLACING FISH MEAL WITH PORCINE GALLBLADDER MEAL ON GROWTH, HEPATIC ANTIOXIDANT CAPACITY, AND LIPID METABOLISM IN JUVENILE RICE FIELD EEL (MONOPTERUS ALBUS)

To evaluate the effects of replacing fish meal with porcine gallbladder meal on the growth performance and health status in juvenile rice field eel [<italic>Monopterus albus</italic>, initial body weight: (30.00±0.01) g], five isonitrogenous and isolipidic experimental diets were formulated with 0 (control, P0), 15% (P15), 30% (P30), 45% (P45), and 60% (P60) of fish meal protein replaced by porcine gallbladder meal. The feeding trial lasted for 8 weeks. Compared to the control, the P15 group showed significantly higher final body weight and weight gain rate, along with a lower feed conversion ratio. In contrast, the P45 and P60 groups exhibited growth suppression and reduced feed efficiency, with the P60 group also showing a significantly increased hepatosomatic index. Intestinal lipase activity was significantly elevated in all replacement groups, while trypsin activity decreased significantly in P45 and P60. Histological examination revealed improved intestinal structure in the P15, whereas structural damage was observed in the P45 and P60. Serum biochemical analysis showed significantly increased levels of TG, LDL-C, GLU, and C4 in all experimental groups. TC levels increased significantly in P45 and P60, while HDL-C and TBA levels significantly decreased. Genes related to lipid synthesis were upregulated across all experimental groups; lipid decomposition and oxidation-related genes were upregulated in P15 but downregulated in P45 and P60. In P15, hepatic inflammatory cytokine expression was downregulated, and antioxidant enzyme activities and related gene expression were upregulated, indicating suppressed inflammation and enhanced antioxidant capacity. Conversely, P45 and P60 exhibited increased expression of inflammatory genes and impaired antioxidant responses. Liver histology revealed pronounced vacuolar degeneration and inflammatory cell infiltration in the high-replacement groups (P45 and P60), along with significantly elevated serum GPT and GOT levels and aggravated structural damage. In conclusion, at a replacement level of 15%, porcine gallbladder powder effectively improved growth performance and overall health status in juvenile <italic>M. albus</italic>, while high replacement levels (≥45%) impair hepatic and intestinal health and disturb lipid metabolism. It is recommended that porcine gallbladder powder substitution not exceed 30% in <italic>M. albus</italic> diets.