Do fish naturally occur in lakes?

When the stream connects with another body of water - another stream or river, a lake or the sea - a fish highway is created. One can imagine that over time fish migrating through and between river systems downstream or upstream to lakes can colonise many different lakes in a large catchment area. It also happens that a new pond forms and the fish bring themselves with it. Even lakes that used to be fish-free, such as high mountain lakes, now have healthy fish populations and often displace the native amphibians.

The fish move to the new area or migrate up the stream to spawn and eventually find their way into the new lake and colonise it.

How do the fish get into the lakes?

Or a river overflowed its banks a long time ago and briefly flooded low-lying land, creating a populated lake. The fish move into the new area or migrate up the river to spawn, and eventually find their way into the new lake and colonise it. Some cultures even have religious New Year customs where fish are released into bodies of water. Similarly, fish roe that stays moist enough on its way from one pond to another can be washed off the skins and feet of native animals.

While this mechanism is primarily responsible for the transfer of river-dwelling fish, it can also move lake fish from one pool to another if they spend part of their life cycle in rivers.

How do the fish get into an artificially created lake?

They then come out of hiding to feed and reproduce, and continue their life cycle until the next dry period. Sometimes a short flood can also flush some fish from other waters nearby into a particular pond, river or lake. Depending on the size of the streams or rivers feeding the lake, they may enter the lake by migrating downstream into the lake if there are fish in the tributaries. Fish and other aquatic life may already be living in a fresh pond (or in a pond that refills after a prolonged drought), but they may not be seen until some time after it is formed.

Why do the fish in a lake come to the surface?

The reason they are at the surface trying to breathe is because of the lack of dissolved oxygen in the water. If you can find areas where the thermocline meets weeds, rocks, structures or cover, you will almost certainly find fish. Perhaps the most common reason fish jump out of a pool is a lack of dissolved oxygen in the water. Salmon are famous for their wonderful aerobatics; other fish do the same, but in a less dramatic way.

The fish need a high level of dissolved oxygen in the water to breathe and may jump out of the tank in the hope of finding a more oxygen-rich environment.

References:

Amie Pross

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