急性离水操作胁迫对四指马鲅(Eleutheronema tetradactylum)幼鱼组织结构和氧化应激的影响

The Effects of Acute Off-Water Handling Stress on the Tissue Structure and Oxidative Stress of Juvenile Eleutheronema tetradactylum

关键词:  四指马鲅  操作胁迫  抗氧化酶  Na+-K+-ATP酶

Key words:  Eleutheronema tetradactylum  Handling stress  Antioxidant enzymes  Na+-K+-ATPase

摘要:

为探究急性离水操作胁迫对四指马鲅(Eleutheronema tetradactylum)幼鱼组织结构和氧化应激的影响，本研究通过组织切片和酶活性测定来观察及检测鳃和肌肉显微结构的变化、抗氧化酶活性以及Na+-K+-ATP酶活性，以探究四指马鲅应激反应规律。结果显示，急性离水操作胁迫2 h后，鳃小片、扁平上皮细胞以及线粒体丰富细胞都出现不同程度的损伤；肌肉从肌纤维变性、肌纤维束之间的间隙增宽、空泡化至肌肉组织整体失去固有形态，并且呈逐渐分解的趋势；超氧化物歧化酶(SOD)和还原型谷胱甘肽(GSH)有相同的变化趋势，胁迫后的2 h显著下降(P<0.05)，但12 h时则升至最高值。过氧化氢酶(CAT)和总抗氧化能力(T-AOC)水平在处理后2 h无显著变化(P>0.05)，之后升高，直到12 h达到峰值。丙二醛(MDA)含量在胁迫后的2 h无显著差异(P>0.05)，直到6 h达到峰值。SOD和CAT活性在处理24 h后显著低于处理前，其他酶变化不显著。Na+-K+-ATP酶活性在处理后2 h显著升高(P<0.05)，12 h达到峰值，24 h恢复到处理前水平。本研究表明，操作胁迫会对鳃和肌肉的组织结构造成损伤，而且随时间持续，损伤呈现加重趋势；肌肉抗氧化酶系统在受到氧化压力2 h后才启动，处理后12 h肌肉受到的氧化压力最大，抗氧化酶活性最强；在受到外界刺激时，SOD和GSH之间可能存在协同作用；MDA可以作为四指马鲅氧化损伤的快速响应生物标记物。

Abstract:

Eleutheronema tetradactylum is subordinate to Mugiliformes, Polynemida, Eleutheronema in taxonomy. As a new aquaculture species, it has gained popularity in most farmers in recent years because of the delicious meat, the fast growth, the high market value and other advantages. However, this species is prone to stress from the pulling capture and the transport due to its weak anti-stress ability. In order to understand the effects of acute off-water handling stress on the tissue structure and oxidative stress of juvenile E. tetradactylum, we stocked the juvenile fish in the outdoor water tank and stressed them by simulating the pulling capture. The samples were collected at 2 h, 6 h, 12 h and 24 h after the off-water handling stress, and fixed separately with poly formaldehyde and liquid nitrogen. The samples fixed with poly formaldehyde were used in tissue sectioning and we observed the changes in the micro- structure of gills and muscles. The samples fixed with liquid nitrogen were used to examine the activities of antioxidant enzymes in muscles and the Na+-K+-ATPase in gills. Results showed that varying degrees of damages were induced in the gill lamella, the squamous epithelium cells and mitochondrion-rich cells (MRC) in 2 h after stress. Firstly, the muscle fiber necrosis appeared and then the gap of muscle fiber became widened, followed by vacuolation and even muscle fiber loss. Superoxide dismutase (SOD) and glutathione (GSH) had the same changing pattern, which was a significant drop (P<0.05) in 2 h after stress, followed by the rise to the highest level 12 h later. Then they began to decline slightly lower than the control level at 24 h. Catalase (CAT) and total antioxidant capacity (T-AOC) did not change significantly (P>0.05) at the beginning of 2 h, but then it rose to a highest value at 12 h and subsequently recovered to the normal level at 24 h. The content of malondialdehyde (MDA) did not have a marked change (P>0.05), and it reached the highest value at 6 h, and then fell back to the normal value at 24 h. The activity of Na+-K+-ATPase was elevated (P<0.05) at 2 h, stayed stable, and rose again until 12 h when it reached the highest value, then it went back to the normal value at 24 h. In conclusion, muscles and gills of E. tetradactylum will be damaged by acute off-water handling stress; besides, the damage will deteriorate as the off-water time goes over. The muscle antioxidant enzyme system will only be activated at 2 h after the handling stress. The synergy may exist between SOD and GSH when the organism was stressed by external factors. At 24 h after the stress, the activities of SOD and CAT will be in a state of equilibrium and the values will be significantly lower (P<0.05) than the control level, and this explains that antioxidant enzymes were affected to certain extent by off-water handling stress. In addition, MDA, the degrading product of peroxide lipid, can be used as a biological marker of rapid stress response in E. tetradactylum. Na+-K+-ATPase in gills can provide energy support during this process to improve the anti-stress ability of E. tetradactylum.