Fishes Spawning In The Wild

Updated during November, 2023.

Warning! This article includes personal opinions and speculations!

In the wild, the daily weather fluctuations and seasonal changes, usually, makes the environment in natural freshwater habitats vary more than in an aquarium. Rainy seasons and dry seasons are examples of large changes in the natural environment of many freshwater fishes.

To many marine saltwater fishes, the spawning is sometimes related to the moon cycle, since many marine saltwater organisms spawn at the same time during the full moon.

To many (but not all) freshwater fishes, it can be important to adapt their spawning to a time when the supply of food is good, both for the fry and the parents, and/or the odds for successfully getting surviving eggs and fry are also good. This, often (but not always), means the rainy season, for many tropical freshwater fishes, while it, usually, means the spring season for many subtropical freshwater fishes. When the lifegiving water is of good quality and gradually becomes filled with tiny organisms, that the fry, juveniles and parents may eat to grow. They may need to thoroughly prepare in advance, for the other yearly seasons ahead, with harsher conditions during dry season, or winter season.

Factors that trigger spawning in tropical freshwater fishes that spawn during the rainy season are, for example, the temperature of the water, pH value, hardness value, oxygen gas content, water level, water flow, food supply (some species even need to eat special types of food, to spawn), availability of appropriate spawning sites (that are, perhaps, above water level and unavailable during the dry season), the diurnal rhythm, atmospheric pressure, other fishes that spawn, etc.

Some fishes (but not all), seem to have a "biological clock", that triggers spawning only at a certain time of year. Different species are different, in their level of sensitivity to their "biological clock". After a few generations in captivity, sometimes with the use of artifical means (some fish farmers use hormones and massaging techniques, instead of letting the fishes get ready and spawn "naturally") the "biological clock" may becomes less important, and/or unsynchronized with the seasons in the wild.

If you want a "stubborn" species of fish to spawn "naturally" in your aquarium, especially if it is wild caught and not known to breed without artifical means in captivity, to "crack the code" on what makes them spawn, you may have to consider all triggering factors, that makes that perticular species spawn in the wild.

Sometimes, it may not be enough to only simulate the wild conditions of the spawning season, since the other seasons of the year may also hold some puzzle pieces, as part of the process, to fully prepare and get the fishes ready and eager to spawn.

For fishes in the wild, it is a struggle to survive as a species, according to the principle of "survival of the fittest". The most sensitive time is as eggs and fry. It is, usually, only a small number, of the original amount of fertilized eggs, that survive, to become larvae, fry, juveniles and, eventually, adult fishes.

The fishes have developed methods to ensure reproductive success. Evolution has led to some species laying thousands of eggs, where the chance for any particular fry to survive is very low, but the large amount of eggs ensures that there are still a few survivors.

Other fishes have bet their heritage on another method, to lay only a few eggs. These species often protect this smaller amount of eggs and fry. These eggs are often a lot larger and one, or both, of the parents sometimes guard the offspring, until the fry are large enough to take care of themselves. Yet, other fishes have adapted by giving birth to live young, instead of laying eggs.

The fishes have different enemies and dangers to overcome in the wild. There are predators, drought, diseases, rivals, lack of food, water quality issues and so on. They must also find an appropriate fish of the same species, but the opposite gender, to reproduce with, so that the species may live on and keep adapting through the generations. Through natural selection, the genes of individuals that never succeed to get their offspring to survive, will not be passed on to the next generation, but the ones that do succeed makes the cycle of life able to continue, for an other round, in the natural world of fishes!

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