We evaluated the immune response of pacu fed with a β-glucan diet (0.5%) for 10 days. After the feeding period, fish were subjected to handling and 3 h after, inoculated with Aeromonas hydrophila. Fish were sampled before handling (baseline condition), 3, 6, and 24 h and 1 week after inoculation. A higher level of blood glucose was found in fish treated with β-glucan in baseline conditions. Handling and bacterial inoculation increased the circulating levels of cortisol and glucose and promoted the acute inflammatory response (lymphopenia and neutrophilia). β-Glucan prevented the decrease in the respiratory activity of leukocytes observed in the control group at 3 h sampling. β-Glucan did not affect the complement and lysozyme, which were activated 24 h after the bacterial challenge in control fish. A reduction in the number of leukocytes was found in fish treated with β-glucan 1 week after the challenge. We suggest two plausible hypotheses for this event: (1) it could be attributed to a depletion of the immune responses or (2) it could be due to a mobilization of the leukocytes to the spleen for antigen presenting/processing. In general, β-glucan avoided the reduction of the activity of leukocytes after stress and the bacterial challenge and increased the baseline glucose levels. Our findings confirm the immunomodulatory action of glucan and add evidence showing that glucan can have a role in stress response.

我们评估了饲喂β-葡聚糖饮食（0.5％）10天的pacu的免疫反应。喂食期后，对鱼进行处理，并在3小时后接种亲水性气单胞菌。在处理前（基线条件），接种后3、6、24小时和1周对鱼进行采样。在基线条件下，用β-葡聚糖处理的鱼体内发现较高的血糖水平。处理和细菌接种增加了皮质醇和葡萄糖的循环水平，并促进了急性炎症反应（淋巴细胞减少和中性粒细胞增多）。在3小时的采样中，β-葡聚糖阻止了对照组中观察到的白细胞呼吸活性的下降。β-葡聚糖不影响补体和溶菌酶，它们在对照鱼中受到细菌攻击后24小时被激活。攻击后1周，用β-葡聚糖处理的鱼白细胞数量减少。对于此事件，我们提出两个合理的假设：（1）可能归因于免疫应答的减少，或者（2）可能归因于白细胞动员到脾脏进行抗原呈递/加工。通常，β-葡聚糖避免了应激和细菌攻击后白细胞活性的降低，并增加了基线葡萄糖水平。我们的发现证实了葡聚糖的免疫调节作用，并增加了表明葡聚糖可以在应激反应中起作用的证据。