I was sitting at the edge of a small pond in a park the other day, peacefully observing the fish and other tiny aquatic creatures wading and floating in the water. Out of nowhere, a question popped into my head: where did all these little guys come from?
I assumed that the fish in that pond must have had a lot of human help to propagate their species and populate the pond. However, that didn’t really answer the question, because how can you explain the presence of aquatic animals in new water bodies, especially small ones situated in the middle of nowhere?
There are certain places that have large pits or depressions that have turned into ponds following heavy rains or flooding of the region. If you have ever observed that type of water body, you have likely noticed that fish start to appear in them on their own, as if by magic! Since there were no fish in the pond before (as the pond didn’t previously exist), and with absolutely no outside human help, how do fish appear in these ponds and lakes after they form?
Another similar instance occurs with dry ponds. When a pond dries up and its aquatic inhabitants consequently die, how can it suddenly play host to more little creatures when it refills?
Short answer: They either reach the water body through external help, or the creatures stay there, survive the period of drought, and then thrive again when water is plentiful.
How do fish appear in newly formed water bodies?
Fish reach new/replenished pounds in three main ways: they’re already there, they get there naturally, or they have some type of external help getting there.
When fish are already there
This might sound a bit unbelievable at first, but it’s true. Fish and other aquatic creatures might already reside in a fresh pond (or one that refills after being dry for a while), but you might not see them until some time passes after their formation.
There are some species of aquatic animals that lay eggs capable of surviving long spells of drought that will hatch only when they’re locally rehydrated. For instance, algae leave spores that can survive for extended periods of time. There are also certain species that dig deep into the mud of a pond and leave their eggs there. The eggs hibernate until the pond is refilled, at which point they come out, reproduce and propagate their species in the newly formed water body. American alligators survive dry spells in this exact way!
When fish are delivered naturally
A piece of land could have the same drainage system causing different water bodies to share the same water and its inhabitants
Many lakes and ponds are formed by rivers and seas themselves. For instance, if there is a steady upsurge of water in a lake, its water might ‘spill’ over its natural boundaries and accumulate in a low-lying area via small streams. This leads to the formation of a small ‘child’ water body, where fish and other aquatic creatures might travel to through the same streams, which act as a ‘liquid highway’ between the parent river and the newly formed lake. Once there, the newly arrived fish reproduce and populate the new lake/pond.
In many cases, a piece of land will share the same drainage system with many other water bodies. Therefore, many lakes and ponds that seem unconnected when the water level is normal are actually joined in various ways; as a result, they contain basically the same water.
When fish get there with external help
While most aquatic creatures travel to newly formed water bodies through one of the methods mentioned above, there’s one more method (also the most exciting one) of migration that fish use: through the helps of birds, land-based animals and humans.
Through the help of animals
Lakes that are close to each other often get a population boost by hitching a ride on birds that hang out in ponds. For instance, when a bird comes to drink water from a pond, eggs might stick to its feathers/feet. When it flies off to a newly formed pond nearby, which is also a new hang-out spot for many of its pals, those same eggs might uncouple themselves from their host and populate the new pond over time.
The same thing happens in the case of land animals, whose feet and fur might play host to the eggs of aquatic animals for the journey between two ponds.
Through the help of humans
Humans play a crucial role in populating ponds by actively/passively introducing select species of aquatic animals in them. There are dedicated fish farms and hatcheries where populations of certain fish are raised and subsequently delivered to water bodies that need a population boost. Trout is one of the most commonly introduced fish through active human effort, which explains how a small pond in someone’s backyard can have a thriving fish population.
Regardless of a pond’s size, its newness or apparent isolation from other water bodies, the appearance of fish and other aquatic creatures in it can be attributed to one of nature’s many maxims: life will always find a way!