This study was carried out to investigate the effects of dietary vitamin A (VA) on growth performance, antioxidant capacity, digestion, intestinal immune response, and mRNA expression of intestinal tight junction proteins for juvenile hybrid grouper (Epinephelus fuscoguttatus ♀ × Epinephelus lanceolatus ♂). Six isonitrogenous and isolipidic experimental diets were formulated to obtain VA levels (317, 1136, 2038, 4142, 7715, 15204 IU/kg diet, respectively). The triplicate groups of fish (average weight of 9.01 ± 0.27 g) were fed twice daily (8:00 and 16:00) for 7 weeks. Based on the broken-line analysis model of WG and LYZ activity, the dietary VA requirement of hybrid grouper were estimated to be 2688.58 and 4096.36 IU/kg diet. The results showed that VA deficiency or excess could reduce Weight gain, specific growth rate, and protein efficiency ratio, and increase feed conversion ratio and hepatosomatic index (P < 0.05). In addition, VA deficiency could reduce the serum activities of acid phosphatase (ACP), superoxide dismutase, and total antioxidant capacity and increase the malondialdehyde content (P < 0.05). VA deficiency also could reduce intestinal activities of ACP, alkaline phosphatase, lysozyme, complement 3, complement 4 contents, and activities of alpha-amylase, lipase, and trypsin (P < 0.05). Meanwhile, VA deficiency could reduce villus height in proximal intestine (PI) and mid intestine (MI), as well as muscle thickness in PI and distal intestine (DI) (P < 0.05). Moreover, VA deficiency could down-regulated antimicrobial peptides (β-defensin, Hepcidin [not in MI and DI], Epinecidin), anti-inflammatory cytokines (interleukin 10 and transforming growth factor β1 [not in DI]), tight junction proteins (occluding and claudin3) mRNA levels in the PI, MI and DI, and up-regulated pro-inflammatory cytokines (tumor necrosis factor α [not in MI] and interleukin 1β [not in MI]), signaling molecules c-Rel and p65 (P < 0.05). Collectively, VA deficiency could reduce growth performance because of a negative effect on intestinal health by depressing digestive abilities, intestinal morphology, immunity and tight junction function in the intestine.

这项研究旨在研究膳食维生素A（VA）对幼年斑斑石斑鱼（Epinephelus fuscoguttatus♀ ×  Epinephelus lanceolatus）的生长性能，抗氧化能力，消化，肠道免疫反应以及肠道紧密连接蛋白的mRNA表达的影响。♂）。配制了六种等氮和等脂实验日粮以获得VA水平（分别为317、1136、2038、4142、7715、15204 IU / kg日粮）。一式三份的鱼（平均重量为9.01±0.27 g）每天喂两次（8:00和16:00），持续7周。基于WG和LYZ活性的折线分析模型，杂种石斑鱼的日粮VA需求量估计为2688.58和4096.36 IU / kg日粮。结果表明，VA缺乏或过量会降低增重，比生长速率和蛋白质效率比，并增加饲料转化率和肝体指数（P  <0.05）。此外，VA缺乏可降低血清酸性磷酸酶（ACP）活性，超氧化物歧化酶和总抗氧化能力，并增加丙二醛含量（P  <0.05）。VA缺乏还可能会降低ACP，碱性磷酸酶，溶菌酶，补体3，补体4的含量，以及α-淀粉酶，脂肪酶和胰蛋白酶的活性（P  <0.05）。同时，VA缺乏可降低近端肠（PI）和中肠（MI）的绒毛高度，以及PI和远端肠（DI）的肌肉厚度（P <0.05）。此外，VA缺乏可能下调抗菌肽（β-防御素，Hepcidin [不在MI和DI中]，Epinecidin），抗炎细胞因子（白介素10和转化生长因子β1[不在DI中]），紧密连接蛋白（ PI，MI和DI中的occlusion和claudin3）mRNA水平以及促炎性细胞因子（肿瘤坏死因子α[不在MI中]和白介素1β[不在MI中]），信号分子c-Rel和p65（P  <0.05）。总的来说，VA缺乏会降低肠道的消化能力，肠道形态，免疫力和紧密连接功能，从而对肠道健康产生负面影响，因此会降低生长性能。