杀鲑气单胞菌对大西洋鲑游泳行为和血细胞数量的影响

为探讨利用鱼类行为及血细胞数量变化预警杀鲑气单胞菌(Aeromonas salmonicida)病害发生的可行性,监测了生产中感染杀鲑气单胞菌的大西洋鲑(Salmo salar L.)的游泳行为,以及杀鲑气单胞菌攻毒后大西洋鲑血细胞数量的变化。实验采用同一养殖基地和同一批次的大西洋鲑,其中现场实验鱼选自生产车间健康的和感染杀鲑气单胞菌的养殖鱼,攻毒实验中处理组实验鱼每尾背肌注射100μL、浓度为3.05×107CFU/m L的菌液,对照组注射等体积灭菌生理盐水。现场实验表明,感染杀鲑气单胞菌的大西洋鲑临界游泳速度较健康鱼低26.7%(P0.05),摆尾频率与游泳速度的线性回归方程的斜率也存在显著差异(P0.05)。攻毒实验表明,从攻毒的第4天开始,处理组大西洋鲑白细胞、淋巴细胞、单核细胞和粒细胞数量较对照组均发生显著变化,其中第6天的变化最为显著,白细胞总数、粒细胞数分别降低了2.8%和43.9%(P0.05),淋巴细胞数及单核细胞数分别升高了63.3%和23.9%(P0.05),且处理组4种血细胞数随时间呈现显著的线性变化(P0.05)。研究结果表明通过监测大西洋鲑游泳行为(临界游泳速度和摆尾频率)以及血细胞相关指标的变化可快速判断其健康状况,为病害的早期预警提供依据。

The impacts of Aeromonas salmonicida on swimming behavior and numbers of blood cells of Atlantic salmon (Salmo salar L.)

We investigated the feasibility of monitoring the health of Atlantic salmon (Salmo salar L.) to facilitate development of an early warning system for disease. To do this, we recorded changes in the swimming behavior and blood composition in the salmon after challenge with Aeromonas salmonicida. The fish used for the in situ challenge experiments were the same batch from the same farm. Healthy fish and fish infected with A. salmonicida were used for the in situ experiments. Salmon were injected in the dorsal muscle with 100 µL of A. salmonicida at 3.05×10⁷ colony forming units (CFU)/mL per fish (suspended in saline), while the control fish were injected with isotonic sodium chloride (0.9% NaCl, 100 µL per fish). The swimming ability and tail beat frequency measurements of the healthy and sick fish revealed a significant decrease in the critical swimming speed (U_crit) of sick fish compared with healthy fish (~27%, P<0.05). There was also a significant change in the slopes of the correlations between the tail beat frequency and the swimming speed (P<0.05). For the laboratory experiments, comparisons of the leukocyte system were made between groups at each sampling point and among treatment groups for time after challenge, separately. From day 4 after challenge, the total number of leukocytes, lymphocytes, monocytes and granulocytes showed significant changes in the A. salmonicida-challenged groups compared with the control groups. The biggest change occurred on day 6 after challenge, when the number of leukocytes and granulocytes significantly reduced by 2.8% and 43.9% (P<0.05), respectively, compared with the control groups, and the number of lymphocytes and monocytes significantly increased by 63.3% and 23.9% (P<0.05), respectively, compared with the control groups. Additionally, there were significant correlations between numbers of blood cells and the sampling point in the challenged fish(P<0.05). The results of the present study highlight the feasibility of monitoring fish health through use of the following convenient parameters: swimming performance (e.g., U_crit) tail beat frequency, and blood analysis. Our results lay the foundations for an early warning system for fish disease.