Lakes are an important part of the water cycle; all the water in an area collects in them. The fish either enter new lakes and ponds with outside help, or they stay there, survive the drought and then thrive again when there is plenty of water again. For some time, people have been using fish for recreational purposes. In other cases, a new pond is created and the fish bring themselves along.
The fish move into the new area or migrate up the stream to spawn and eventually find their way into the new lake and colonise it.
Do fish occur naturally in lakes?
This question was already addressed by some of the leading natural scientists of the 19th century, such as Charles Darwin, Alfred Russel Wallace and Charles Lyell, who all came to the same conclusion: Water birds must be responsible for the dispersal of fish. While most fish cannot travel very far over land, their eggs survive several hours out of the water. When the stream is connected to another body of water – another stream or river, a lake or the sea – a fish highway is created. Unfortunately, since the lakes are now connected to the sea, the sea lampreys have migrated up the channel and fed on the fish in the lakes.
Are there fish in all waters?
Certain species, such as the very strange African killifish, burrow deep into the mud of a pond and lay their eggs there. The fact that the same type of freshwater fish is found in lakes connected only by salt water proves that the fish did not evolve independently in each lake. Trout is one of the most common fish introduced by humans, which explains how a small pond in a person’s backyard can have a thriving fish population. One can imagine that over time, fish that migrate through and between river systems downstream or upstream to lakes can colonise many different lakes in a large catchment area.