After having one of the highest rainfall seasons in several years, Londolozi has been scattered with numerous ephemeral pans; all providing well-needed respite from the scorching summer days for myriad different animals. As the days continue to shorten and the seasonal minimum temperature briskly dropping, animals have adopted various strategies to survive the winters. The most evident aspect of the change of season in Africa is the scarcity of water as all the waterholes and pans disappear. Our first thought is of hippos and crocodiles but what about the fish species and how they are needing to adapt to survive the winter.
Fish play a vital role within the complex food webs that exist within rivers and waterholes and are essentially the link between land and water food webs. Fish keep the populations of numerous insects in check as they feed on both the larvae and or on the adult water-based insects themselves. Birds, crocodiles, water monitors, small mammals, and even some opportunistic leopards will then feed on the fish; who will, in turn, get preyed upon by other animals on land.
In thinking of Africa and its most prolific hunters, lions, leopards, wild dogs, and such, come to mind first but in fact, there are some less assuming, yet equally deadly, hunters that lurk just below the surface. The African Sharptooth Catfish (Clarias gariepinus) is an expert hunter too. It was one of the first fish described by the British natural scientist, William John Burchell (1782 – 1863) after he first found the species in the Orange River (known locally as the Gariep hence the species name). Growing up to 1.4m (4.5 ft) long and weighing up to 60kg (132 lbs) which, to put in perspective, is significantly bigger than a female leopard. They predominantly prey on other fish but will even eat birds, frogs, reptiles, and even small mammals if they get a chance. Working together as a pack to hunt using their whisker-like protrusions to identify prey in the murky waters, cornering off schools of fish in shallower water before feeding on them. As impressive as their hunting strategies are and varied diet is I think their adaptations for surviving temperature and habitat changes are simply remarkable and more appropriate for this discussion.
A specific characteristic of catfish in the Clariidae family is the ability to absorb oxygen from the air as well as through their gills from the water. This special respiratory organ is located in the upper part of the gill cavity, giving them the facility of surviving in very low oxygenated water sources, as they can venture to the surface to gulp in additional oxygen. Combined with this ability to breathe out of the water, they are also armed with robust bony pectoral fins which they use in unison with a wriggling motion of their bodies to “walk” across the land in search of a new, larger waterhole. These excursions out of water will usually happen during the night as their bodies need to maintain a certain level of moisture and the harsh African sun will dry them out quickly. To combat their need of maintaining moisture these fish will burrow themselves into the mud and are able to secrete a mucus membrane that seals them off to the conditions outside, where they will wait out the dry months and using their lung-like chamber to breathe as opposed to their gills.
So as we head further and further into winter and more waterholes dry up the catfish will start looking for better places to wait out the dry months… can you imagine the good fortune of a predator looking for a quick easy meal and coming across a fish out of water?