This study was conducted to examine the combinatory effects of β-glucan and oxytetracycline (OTC) on hybrid giant tiger groupers (Epinephelus fuscoguttatus × Epinephelus lanceolatus). In in vitro tests, OTC significantly reduced superoxide anion production and phagocytic activity in primary head kidney leukocytes. However, this suppressive effect was alleviated by co-treatment with β-glucan. Subsequently, feeding trials were performed to investigate the potential immunomodulatory effects of dietary β-glucan alone or in combination with OTC on groupers. A total of 210 healthy groupers (368.00 ± 51.03 g) were divided into six groups. Group 1 was the control group, group 2 (BG) received 5 g β-glucan per kg feed weight, groups 3–5 received 5 g/kg β-glucan in combination with 10, 30, or 50 mg OTC/kg fish weight/day (groups M1, M2, and M3, respectively), and group 6 (O) received 50 mg OTC/kg fish weight/day. Fish were sampled to determine the innate immunity parameters and residual OTC levels in the muscle tissue during a 28-day feeding regimen. Residual OTC levels were considerably higher in groups M3 and O compared with the other groups, and peaked on day 14. This was followed by a slight decrease on day 28, despite a continuous supply of OTC. Notably, fish fed with OTC alone had significantly decreased phagocytic rates and superoxide anion production observed in head kidney leukocytes, as well as poorer protection against Vibrio alginolyticus infection. These immunosuppressive effects were not observed in the fish fed with β-glucan in combination with a lower dose of OTC (group M2). Thus, these data suggest that the combination of dietary β-glucan and OTC exerts synergistic immunostimulating effects that protect groupers from bacterial infection.

本研究旨在研究β-葡聚糖和土霉素对杂种巨型老虎石斑鱼（Epinephelus fuscoguttatus  ×  Epinephelus lanceolatus）的联合作用。在体外测试中，OTC显着降低了原发性头部肾脏白细胞中超氧阴离子的产生和吞噬活性。然而，通过与β-葡聚糖共同处理减轻了这种抑制作用。随后，进行了喂养试验，以研究饮食中单独或与OTC组合使用的β-葡聚糖对石斑鱼的潜在免疫调节作用。总共210名健康石斑鱼（368.00±51.03 g）分为六组。第1组为对照组，第2组（BG）每公斤饲料重量接受5 gβ-葡聚糖，第3–5组每公斤鱼体重结合5 g / kgβ-葡聚糖和10、30或50 mg OTC /天（分别为M1，M2和M3组），第6组（O）每天接受50 mg OTC / kg鱼体重。在28天的喂养方案中，对鱼进行采样以确定先天免疫参数和肌肉组织中残留的OTC水平。与其他组相比，M3和O组中的残留OTC水平要高得多，并在第14天达到峰值。尽管持续供应OTC，但在第28天略有下降。值得注意的是，仅用OTC喂养的鱼在头部肾脏白细胞中观察到吞噬率和超氧阴离子产生显着降低，并且对鱼的防护能力较差溶藻弧菌感染。在饲喂β-葡聚糖与较低剂量的OTC（M2组）的鱼中未观察到这些免疫抑制作用。因此，这些数据表明，饮食中的β-葡聚糖和OTC的组合具有协同免疫刺激作用，可保护石斑鱼免受细菌感染。