During a severe drought, rivers and streams tend to dry up but fish and other freshwater organisms need to survive if they are going to be around to re-populate the stream in the next wet period. So, the question to ask is, “Where do they go?’’
The African sharp-toothed catfish is a large, eel-like fish, usually of dark grey or black colouration on the back, fading to a white belly. They are one of the more common fish species found in southern Africa’s rivers and other freshwater sources. These catfish have a unique ability to endure extremely harsh conditions, able to tolerate very low oxygen concentrations and can even survive for considerable periods out of water. They do this using a specialised suprabranchial organ. This organ is a large, paired chamber with branches above the gill arches specifically adapted for air breathing which enable it to move over land even when not forced to do so by drought. They are also able to endure a wide range of PH balances, salinities of 0-10% and water temperatures of 8-35°C.
During periods when drought sets in, environmental conditions force the catfish to move out of dried-up riverbeds, seeking wetter areas. They will take refuge in places that stay adequately wet for months or years until the stream is replenished by the first rains. For example, in pools or waterholes within stream channels, on floodplains, streambed sediments, bank burrows and mud flats.
These catfish are also able to breathe by a process called cutaneous respiration. To do this, they will bury themselves in mud, encapsulate themselves in a mucus slime and stay that way, suspended for an entire year or more, absorbing oxygen through the permeable skin they possess for this very purpose. When the rains return, they will be the only fish in the pond. The ability to breathe out of water as well as under and to tolerate extreme conditions make it one of the most adaptable fish species to live in our water sources.
Sources: (Safriel & Bruton 1984, Hecht et al. 1988)