Reproduction is one of the most important phenomena on our planet. Moreover, from the most ancient times, it has two types. According to scientists, this is an asexual species of reproduction that appeared on Earth at least 3 billion years ago. In addition, the second type was the sexual type. This method of procreation first appeared for about one and a half billion years. Over the course of millions of years, these methods have evolved and assumed a wide variety of forms. Thanks to this, today there are many different land and aquatic life forms that have a unique method of reproduction. For example, mating fish can be of several species. Some of them reproduce offspring through parthenogenesis, while others reproduce histogenesis.
In this article we will look at how fish mate, what methods exist and what is their fundamental difference.
The structure of the reproductive system
To understand how the process of mating fish is carried out, you need to consider in detail some features of their reproductive system. According to statistics, the bulk of the fish inhabiting the waters of the oceans are dioecious. It is about eighty percent of all individuals. However, science also knows such species where it is possible to observe a change in the sexes of fish. In these cases, the female can turn into a male.
The genitals of the male are expressed by paired testes. Ducts depart from them, ending with an opening responsible for the performance of sexual functions. When the mating period begins, a huge amount of sperm accumulates in the ducts of males. At the same time, eggs mature in the genitals of the female, expressed by paired ovaries. Mating in fish occurs as soon as the eggs have reached the necessary maturity. It is noteworthy that the amount of caviar directly depends on several factors, such as the type of fish, its size and age.
Sexual reproduction of fish
Sexual reproduction can have a very different form, depending on the type. The basic principle is the fusion of the gametes of the male and the female, which occurs after the pairing of fish. As a result of this, the so-called zygotes appear, and after the full development of the fry occurs. The embryo is formed as a result of zygote division. When the eggs reach their maturity, the fish, having the appearance of a larva, leave it. Initially, they exist thanks to the yolk sac, which gradually dissolves, providing development and nutrition. After the yolk finally disappears, the larva passes to the next stage - male. At this stage of development, it can feed on unicellular organisms and small crustaceans, for example, daphnia. With the development of fry, his diet also changes. As a result of this, it differs from adults only in size.
Types of Fertilization
The process of fertilization can be of two types: external and internal. In the main part of fish species, this process is carried out externally in an aquatic environment. Female specimens spawn, and males, in turn, fertilize it with sperm. However, there are fish species that have internal fertilization. These include perches that live in salt ponds, and guppies, which have gained wide popularity among fans of aquariums. In this case, fertilization occurs due to modified anal fins, which are called gonopodia. Often this method of reproduction is accompanied by live births. There are certain advantages to this, as the offspring born in the womb are protected from predators. In addition, immediately after birth, it is adapted for independent search and consumption of food.
Parthenogenesis
Parthenogenesis is one of the types of reproduction in which the sperm does not participate in the fertilization of eggs. Moreover, this method is considered to be sexual, because in the process of reproduction one sex gamete is involved. The egg in this case can develop autonomously to the stage of division. After that, she begins to interact with fertilized eggs and is activated. Due to this feature, unfertilized caviar does not adversely affect the masonry and does not rot. Parthenogenesis occurs in the following species:
- sturgeon;
- cyprinids;
- salmon.
Histogenesis
In turn, histogenesis is a reproduction method involving sperm. In this case, the activation of the egg is stimulated by its interaction with the sperm of a male of a different species, related to this. After the sperm is in the egg, it stimulates its division. However, the whole process takes place without nuclear fusion. It is noteworthy that the egg in this case becomes a female organism. Male individuals do not form during histogenesis. Histogenesis is mainly found in silver carps and mollies. In this case, the stimulator for them is the sperm of roach and cyprinids.
