Dietary niacin supplementation enhances growth and osmoregulation of Nile tilapia (Oreochromis niloticus) under hyperosmotic stress improving ion homeostasis and carbohydrate metabolism

The aim of this experiment was to investigate the effects of dietary niacin supplementation on the growth, osmoregulatory capacity, and energy metabolism of Nile tilapia (Oreochromis niloticus) under salinity stress. In this study, five diets with varying niacin concentrations were prepared, with practical niacin levels of 3.33, 12.18, 33.98, 94.28, and 275.23 mg/kg. Fish with an initial weight of 1.80 ± 0.22 g were selected for an 8-week feeding trial under 20 psu salinity. The results indicated that the dietary niacin significantly increased the weight gain, specific growth rate, and condition factor of tilapia. Furthermore, niacin supplementation also increased the crude protein and crude fat contents of tilapia. 12.18–94.28 mg/kg dietary niacin significantly improved the ion transport capacity of the gills which is a main tissue of the osmoregulation. Histological analysis of gill revealed that dietary niacin at concentrations ranging from 12.18 to 275.33 mg/kg relieved structural damage from salinity stress. After ingestion, niacin primarily accumulated in the liver and gills, activating the niacin metabolic pathway. As a result, compare to the control group, fish fed with dietary niacin got higher level of NAD⁺, NAD⁺/NADH. The addition of 94.28 mg/kg niacin affected the glycolysis, TCA cycle and gluconeogenesis processes through SIRT1/GLUT1/HK signaling pathway. In addition, content of liver glucose was decreased, while pyruvate and ATP contents were increased. Optimal dietary niacin could improve the growth performance of Nile tilapia under salinity stress by activating the carbohydrate metabolism by SIRT1/GLUT1/HK signaling pathway. It can also enhance the salinity tolerance by activating ion transportation. Based on the second−order polynomial regression analysis with weight gain rate and specific growth rate, the optimal dietary niacin for Nile tilapia under salinity stress is 151.67–171.73 mg/kg.