DIETARY GLYCINE ZINC ADDITION ON GROWTH PERFORMANCE, ZINC METABOLISM, AND SUMOYLATION MODIFICATION IN THE INTESTINE OF LARGEMOUTH BASS (MICROPTERUS SALMOIDES)

Zinc, as an essential trace element, plays a crucial role in fish growth, antioxidant defense, and post-translational modifications of protein. Both excessive and insufficient zinc levels can negatively impact physiological functions. Therefore, determining the optimal zinc requirement for fish is of paramount importance. Glycine zinc, characterized by its high bioavailability, serves as a zinc source in fish feed. This study investigated the effects of dietary glycine zinc levels on the growth performance, intestinal zinc metabolism, and small ubiquitin-like modifier (SUMO) modification of largemouth bass, aiming to determine the optimal zinc requirement for this species. Six diets containing zinc at levels of 25.27, 34.27, 44.08, 61.92, 99.81, and 168.92 mg/kg were formulated and fed for 14 weeks. Results indicated that the best growth performance was achieved at dietary zinc level of 61.92 mg/kg. Broken-line regression model revealed optimal dietary zinc requirements of 60.28 mg/kg for specific growth rate (SGR). Intestinal zinc content increased with dietary zinc levels, accompanied by upregulation of zinc transporter genes (zip4, zip8, zip9, znt2, znt5, znt7) and metallothionein-related genes (mt, mtf-1). At low zinc levels, shorter intestinal villi height impaired intestinal absorption capacity. With increasing dietary zinc supply, mRNA expression of sumo1, sae1, ubc9, and pias1 increased, while senp2 and senp5 mRNA expression decreased. This study determined the dietary zinc requirements of largemouth bass and revealed that varying dietary zinc levels significantly impact growth performance, intestinal zinc metabolism, histology, and SUMOylation levels. These findings provide basis for optimizing feed formulations and enhancing zinc utilization, while offering new insights into the relationship between zinc metabolic regulation and SUMOylation modification in fish.