Changes of cortisol and lysozyme levels in Carassius auratus blood after crowding stress and the fish sensitivity to pathogen
Changes of cortisol and lysozyme levels in Carassius auratus blood after crowding stress and the fish sensitivity to pathogen
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拥挤应激后鲫鱼血液中皮质醇和溶菌酶水平的变化及对病原菌的敏感性
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发表时间：
2004
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通讯作者：
Cai Tao
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作者：
Cai Tao
自然渔业和集约化养殖系统的压力问题是科学调查的一个主要主题。据报道，鱼类对不同应激的生理反应之一是刺激下丘脑-垂体-肾间轴(HPI)，循环皮质醇浓度增加，这可以被认为是鱼类应激的一般和内分泌指标。众所周知，硬骨鱼对入侵生物具有多种特定和非特定的防御机制。当病原体穿透动物的身体屏障时，它遇到的第一道防线是非特异性免疫系统的防线。化学防御系统攻击病原体，或使其被非特异性免疫系统的细胞成分进一步破坏。因此，鱼类的非特异性免疫系统在抵抗疾病方面具有重要意义，值得更多的关注。溶菌酶是一种特性良好的蛋白质，通过攻击细菌细胞壁从而引起裂解和刺激细菌的吞噬作用而具有抗菌作用(特别是对革兰氏阳性细菌)，因此溶菌酶作为一种天然免疫成分在抵抗病原微生物的入侵方面发挥着重要作用。拥挤应激是水产养殖业中普遍存在的一种慢性应激，近年来受到了广泛的关注。鉴于皮质醇和溶菌酶对鱼类的重要影响，因此选择这两项指标在拥挤应激后进行检测。将160尾鱼随机分为13个玻璃纤维水箱(每个水箱12尾)：拥挤前1个水箱(无关对照组)，对照组4个水箱(7.5g/L)，低密度组4个水箱(15g/L)，高密度组4个水箱(80g/L)。在拥挤应激后第3、10、20、30天分别测定鲫鱼血液中皮质醇和溶菌酶的水平，并在每次采样后计数因感染嗜水气单胞菌而引起的死亡率。结果表明，高密度组大鼠应激后第3天血皮质醇水平显著升高(P0.005)，随后略有下降，但在第30天仍维持在较高水平(平均216.32 ng/mL)。在拥挤后第3天，与对照组相比，血液溶菌酶水平略有升高，但长期应激显著抑制其水平(P0.01)。嗜水气单胞菌感染死亡率与拥挤时间呈正相关。最后一次抽样时，高密度组的平均死亡率为58.3%，显著高于对照组的16.7%。提示短期应激后血皮质醇水平与溶菌酶水平呈正相关，长期应激后血皮质醇水平与溶菌酶水平呈负相关。此外，抗病能力也受到拥挤胁迫的抑制。
The problem of stress in both natural fisheries and in intensive cultivation systems is a major subject of scientific investigation. It is reported that one of the fish's physiological response to different stresses is a stimulation of the hypothalamic-pituitary-interrenal (HPI) axis, with a increase in the concentration of circulating cortisol, which can be considered as both general and endocrine indicator of stress in fish. As is known, teleost fish possess a variety of specific and non-specific defence mechanisms against invading organisms. When a pathogen penetrates the physical barriers of the animal, the first defence lines it encounters are those of the non-specific immune system. Chemical defences attack the pathogen or may opsonise it for further destruction by the cellular components of the non-specific immune system. Therefore, the non-specific immune system of fish is important in resistance to disease and is worthy of more attention. Lysozyme is a well-characterized protein, having an antibacterial effect (particularly on Gram-positive bacteria) both by attacking the bacterial cell wall, thereby causing lysis, and by stimulating phagocytosis of bacteria, so lysozyme as an innate immune component plays an important role in resisting the invasion of pathogenic microbes. Crowding stress, a kind of chronic stress, is so common in aquaculture that in recent years it has received much attention. In view of the important effects of cortisol and lysozyme on fish, the two indexes were therefore chosen to test after crowding stress. In the present study, about 160 fish were randomly allocated into 13 fiberglass tanks (12 fish per tank): one tank for control group before crowding (unrelated control group), four tanks for control groups (7.5 g/L), four tanks for low density groups (15 g/L) and four tanks for high density groups (80 g/L). Cortisol and lysozyme levels in Carassius auratus blood were measured at the 3rd, 10th, 20th and 30th days after crowding stress, and the mortalities due to Aeromonas hydrophila infection were also counted post every sampling. The results indicated that the blood cortisol level increased remarkably at third day after stress (P0.005), then decreased slightly, but still maintained a high concentration (216.32 ng/mL average) in high density group at 30th day. At third day after crowding, blood lysozyme level had a little elevation, but it was inhibited markedly by long term stress in comparison with control group (P0.01). Mortality due to A. hydrophila infection had a positive correlation with crowding time. At the last sampling, the average mortality of high density group was (58.3%,) which was statistically higher than that of control group (16.7% only). It is suggested from the present study that, blood cortisol level and lysozyme level are a positive correlation after short term stress, whereas have a negative one post long term stress. In addition, the resistance ability to disease is also depressed by crowding stress.