PHYSIOLOGICAL ADAPTIVE-MECHANISMS OF CATFISH (SILUROIDEI) TO ENVIRONMENTAL-CHANGES

Emphasis on physiological adaptations to environmental changes in the catfish (Siluroidei), is a rather recent development like that of thei r use in aquaculture. The siluroid fishes with smooth scaleless skin a nd sensory barbels are adapted to live in a variety of aquatic environ ments ranging from freshwater and brackishwater to swamps and marshes both in temperate and tropical regions. However, very little has been explored on their expected wide range of physiological adaptations. Mo st of the results obtained in siluroid fishes are similar to those rep orted for other teleosts such as cypriniform species. However, there a re some air-breathing siluroids, found in the tropical areas, with acc essory air-breathing organs. Besides tolerating periods of water depri vation, some of these fishes have been shown to possess special physio logical and biochemical adaptive mechanisms to tolerate a wide range o f adverse physico-chemical conditions in the ambient environment. Some of the physiological adaptive mechanisms of Siluroidei in general, an d air-breathing species in particular, to important physico-chemical f actors such as oxygen, temperature, ammonia and xenobiotics are review ed and discussed.