Within the water as well, there is a rich profusion of species to be found, none more important than the fishes. Fish are an important source of food for crocodiles and various water birds and are also species by which one can measure the health of an ecosystem. Fish communities, and specific species, are excellent indicators of biological and ecological integrity due to their continuous exposure to water conditions. Fishes display an array of biotic responses to certain levels of toxicity in the water.
In modern time, pollution of rivers is a reality and two of the biggest contributors to the degradation, phosphorus and nitrogen, reach the rivers through, among other things, human waste. The abundance of phosphorus and nitrogen in the system causes algae to grow profusely. When the algae bloom becomes too much, it dies and decomposes, taking the oxygen out of the water. Various species of freshwater fish feed on algae and the pressure of this algae growth can be alleviated by these fish. This feeding behaviour will neutralise the growth of algae, creating equilibrium in the environment.
One of the most abundant species of this river are the Mozambique Tilapia, the sharp tooth catfish and the smallmouth yellowish. To explain the behaviour of these species I am going to use land animals as a comparison. The Mozambique Tilapia: These fishes are quite small and feed on a variety of different food sources. They will eat smaller fish and vegetation and can be compared to the side striped jackal. Always on the prowl looking for any opportunity to pounce.
Mozambique Tilapia. Image courtesy of Wikipedia
The Sharptooth catfish: This is the largest freshwater fish in South Africa and one of the apex predators (let’s not forget the crocodile) of the Sand River. These fish hunt other medium-sized fishes and will go as far as eating smaller mammals and water birds. Their slumbering movement patterns and explosive power means that they are not to unlike the lion.
Sharptooth Catfish. Image courtesy of fishthesea.co.za
The Smallmouth Yellowfish: Powerfully built, streamlined and always waiting for an opportunity, the smallmouth yellowfish is the leopard of the watery unknown. Yellowfish hide behind boulders and freshwater vegetation, waiting for the ideal moment to make their move and hunt down unsuspecting fishes.
Smallmouth Yellowfish. Image courtesy of feathersandfluoro.com
Although seldom seen, especially on a game drive, fish are vitally important to the health of the Sand River and consequently the entire ecosystem, regardless of whether they’re in this African river, a lake, an ocean or pond. The great network that is a natural ecosystem includes all facets of the environment. This foodweb includes all species, including the small fishes that feed on algae every day. As crazy as sounds, these fishes – as well as a multitude of other diminutive species – give us the opportunity to view the magical bigger species strolling to the Sand River in the blistering sun by keeping the fragile ecosystem in relative homeostatis. Next time you pass by or over a body of water, take a moment to appreciate some of the less glamorous species that make our planet so precious.