Vitamin D₃ (VD₃) is an essential nutrient for fish and participates in a variety of physiological activities. Notably, both insufficient and excessive supplementation of VD₃ severely impede fish growth, and the requirements of VD₃ for fish vary considerably in different species and growth periods. The present study aimed to evaluate the appropriate requirements of VD₃ for juvenile grass carp (Ctenopharyngodon idella) according to growth performance and disease prevention capacity. In this study, diets containing six supplemental levels of VD₃ (0, 300, 600, 1200, 2400, and 4800 IU/kg diet) were formulated to investigate the effect(s) of VD₃ on the growth performance, antioxidant enzyme activities, and antimicrobial ability in juvenile grass carp. Compared with the VD₃ deficiency group (0 IU/kg), the supplementation of 300–2400 IU/kg VD₃ significantly enhanced growth performance and increased antioxidant enzyme activities in the fish liver. Moreover, dietary supplementation of VD₃ significantly improved the intestinal health by manipulating the composition of intestinal microbiota in juvenile grass carp. In agreement with this notion, the mortality of juvenile grass carp fed with dietary VD₃ was much lower than that in VD₃ deficient group upon infection with Aeromonas hydrophila. Meanwhile, dietary supplementation of 300–2400 IU/kg VD₃ reduced bacterial load in the spleen and head kidney of the infected fish, and 1200 IU/kg VD₃ supplementation could decrease enteritis morbidity and increase lysozyme activities in the intestine. These findings strengthened the essential role of dietary VD₃ in managing fish growth and antimicrobial capacity. Additionally, based on weight gain ratio and lysozyme activities, the appropriate VD₃ requirements for juvenile grass carp were estimated to be 1994.80 and 2321.80 IU/kg diet, respectively.

维生素D ₃ (VD ₃ )是鱼类必需的营养素，参与多种生理活动。值得注意的是，VD ₃的补充不足和过量都会严重阻碍鱼类生长，而且不同品种和生长时期鱼类对VD ₃的需求量差异很大。本研究旨在根据生长性能和防病能力评价草鱼幼鱼对VD ₃的适宜需求量。在本研究中，配制了含有六种补充水平的 VD ₃（0、300、600、1200、2400 和 4800 IU/kg 饮食）的日粮，以研究 VD ₃对生长性能、抗氧化酶活性的影响和幼草鱼的抗菌能力。与VD ₃缺乏组（0 IU/kg）相比，补充300-2400 IU/kg VD ₃显着提高鱼肝脏的生长性能和抗氧化酶活性。此外，膳食补充 VD ₃通过控制草鱼幼鱼肠道微生物群的组成，显着改善肠道健康。与这一观点相一致的是，饲喂VD ₃的幼鱼在感染嗜水气单胞菌后的死亡率远低于VD ₃缺乏组。同时，饲料中添加300-2400 IU/kg VD ₃可以减少受感染鱼的脾脏和头肾中的细菌负荷，而添加1200 IU/kg VD ₃可以降低肠炎发病率并增加肠道中溶菌酶的活性。这些发现强化了膳食 VD ₃在管理鱼类生长和抗菌能力方面的重要作用。另外，根据增重率和溶菌酶活性，估计草鱼幼鱼适宜的VD _{3需要量分别为1994.80和2321.80 IU/kg日粮。}