Low oxygen concentration is a common feature occurring in a wide range of aquatic systems and in varied ranges depending upon temporal frequency, seasonality and persistence of a place. There have always been naturally occurring low oxygen condition in freshwaters of tropical countries like India. Moreover, anthropogenic activities, related primarily to organic and nutrient enrichment, have led to increase in hypoxia and anoxia both in fresh and in marine system. The fishes in a tropical country like India are quite frequently exposed to this. Aquatic organisms which are frequently exposed to hypoxia show adaptations at all the three levels, namely behavioural, morphological and physiological. To assess the effect of hypoxia at physiological level, change in anaerobic and aerobic enzyme activities and protein profiling in selected tissues of air-breathing catfish, Heteropneustes fossilis, was undertaken. Fish were exposed to experimentally provoked hypoxia for different durations and were killed to study the effect of hypoxia on selected enzymes activities in heart, liver, brain and muscle. Significant changes were recorded. The observations indicated that different tissues respond differently to the stress of hypoxia and the enzyme activity responds in a tissue-specific manner.

低氧浓度是广泛的水生系统中普遍存在的特征，并且取决于时间的频率，季节和场所的持久性而在不同的范围内发生。在印度等热带国家的淡水中，自然一直存在着低氧状况。此外，主要与有机和营养富集有关的人为活动已导致新鲜和海洋系统缺氧和缺氧的增加。在像印度这样的热带国家，鱼类经常暴露于这种情况。经常缺氧的水生生物在行为，形态和生理三个方面均显示出适应性。要在生理水平评估缺氧的影响，进行了化石杂种。将鱼暴露于实验激发的缺氧时间不同，然后杀死鱼以研究缺氧对心脏，肝脏，大脑和肌肉中某些酶活性的影响。记录了重大变化。观察结果表明，不同组织对缺氧应激的反应不同，酶活性以组织特异性的方式反应。