How do fish reproduce?
Fish are marine vertebrate animals, abundant and diverse in the different oceans, lakes, and rivers of our planet. Many of them are part of the diet of humanity, while others can become pets.
These are eukaryotic animal species. They breathe through gills and are endowed with fins instead of legs, distributed differently throughout their bodies.
Fish are only a fraction of the aquatic animals that exist, that is, they are immersed in complicated dynamics of predation and competition. For this reason, the reproduction of fish is not an ecologically simple matter.
In reproduction, courtship strategies to attract the female are common, such as dancing, nest making, etc. In addition, the different species developed diverse methods to ensure the perpetuity of the species.
The reproduction is almost always sexual, since fish, as the great common of animals is born with a certain (female-male) sex. In general, it occurs in three different ways: oviparous, viviparous, and ovoviviparous. We will see each of them below.
Types of fish reproduction
As we said before, fish reproduce in three different ways, depending on the specific species we are talking about. These modes are:
- Oviparous reproduction. As its name suggests, it is about reproduction by eggs, which is the most common in the species of fish that exist. This generally occurs through external fertilization strategies, that is, the female deposits her eggs in the environment, and then the male fertilizes them with his sperm. There are also rare cases where the eggs are fertilized within the female through intercourse.
- Viviparous reproduction. This type of reproduction, similar to that of human beings, involves the internal fertilization of the female, the maturation of the offspring inside it thanks to the nutrition via the placenta, and then its expulsion through a birth canal, ready to start. his independent life. Only about 53 families (around 900 species) of fish have this type of reproduction, which has the evolutionary advantage of ensuring that the young go out into the world as mature as possible.
- Ovoviviparous reproduction. This is a method of reproduction that combines the previous two in a certain way: the female lays eggs inside, which are internally fertilized by the male during copulation. Juveniles grow inside these eggs, without the need for maternal placentas, until they are ready to hatch the eggs. Only then does the female deposit them into the environment, or even expel them into the water around her moments before or after birth.
In the vast majority of cases, fish have separate and well-defined sexes. However, there are species in which hermaphroditism is common, that is, they present both sexes or alternate between one and the other in some stage of their sexual maturation.
Some species, for example, grow up as females and at some point in their adult life “change their sex” (proterogynous species), so to speak, or vice versa (protandric species). In contrast, simultaneous hermaphroditism, in which an individual has both functional sexes at the same time, is extremely rare invertebrate animals
Breeding migrations of fish
Migratory species are those that make long trips or movements for the sole purpose of reproduction or spawning. Some even alternate between fresh and salty waters in this movement, something that they would not normally do in their daily lives.
The classic example is salmon, a sea fish that, once it has reached sexual maturity, travels upstream against the current until it reaches its customary spawning grounds. They do this difficult movement by jumping upstream, an opportunity that many of their predators on land take advantage of to get their prey.