Reproduction is one of the most important phenomena on our planet. At the same time, from the most ancient times, it has two types. According to scientists, this is an asexual form of reproduction that appeared on Earth at least 3 billion years ago. In addition, the second type was the sexual type. This way of procreation first appeared about one and a half billion years. Over millions of years, these methods have evolved and taken on a wide variety of forms. Because of this, today there are many different terrestrial and aquatic life forms that have a unique way of reproduction. For example, the mating of fish can be of several types. Some of them reproduce by parthenogenesis, while others by 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 mating process worksfish, you need to consider in detail some features of their reproductive system. According to statistics, the bulk of the fish that inhabit the waters of the world's oceans are dioecious. We are talking about almost eighty percent of all individuals. However, science also knows such species where you can observe the change of sexes of fish. In these cases, the female can transform into a male.
The genitals of the male are expressed by paired testicles. The ducts depart from them, ending with an opening responsible for the performance of sexual functions. When the mating period of fish comes, a huge amount of spermatozoa accumulates in the ducts of males. At the same time, eggs ripen in the genital organs of the female, expressed by paired ovaries. Mating in fish occurs as soon as the caviar has reached the required 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 take many forms, depending on the type. The basic principle is the fusion of male and female gametes that occurs after the mating of fish. As a result of this, the so-called zygotes appear, and then the fry develop fully. The embryo is formed as a result of division of the zygote. When the eggs reach their maturity, the fish that look like larvae leave it. At first, 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 - fry. At this stage of development, it can feed on unicellular organisms and small crustaceans, such as daphnia. With the development of the fry, its diet also changes. As a result, 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 the fish species, this process is carried out externally in the conditions of the aquatic environment. Females spawn, and males, in turn, fertilize it with sperm. However, there are species of fish in which fertilization is internal. These include perches that live in s alt water bodies, and guppies, which have gained wide popularity among aquarium lovers. In this case, fertilization occurs due to modified anal fins, which are called gonopodia. Often this method of reproduction is accompanied by live birth. This has certain advantages, since the offspring nurtured in the womb are protected from predators. In addition, immediately after birth, it is adapted to independently search for and eat food.
Parthenogenesis
Parthenogenesis is one of the types of reproduction in which the spermatozoon does not take part in the fertilization of the eggs. Moreover, this method is considered to be sexual, because one sex gamete is involved in the process of reproduction. The egg in this case can develop autonomously to the stage of division. After that, she begins to interact with fertilized eggs andis activated. Due to this feature, unfertilized eggs do not adversely affect the laying and do not rot. Parthenogenesis occurs in the following species:
- sturgeon;
- carp;
- salmon.
Histogenesis
In turn, histogenesis is a method of reproduction involving the sperm. In this case, the activation of the egg cell is stimulated by its interaction with the sperm of a male of another species related to this one. After the sperm is in the egg, it stimulates its division. However, the whole process takes place without the fusion of nuclei. It is noteworthy that the egg in this case becomes a female organism. Male individuals are not formed during histogenesis. Histogenesis is mainly found in silver carps and mollies. In this case, the stimulant for them is the sperm of roach and cyprinids.
Some interesting facts
Many aquarium lovers, who are fond of breeding exotic species, always keep a cockerel fish. This is practically the only species of fish on the planet that has a kind of romantic context during the breeding season. Mating betta fish is accompanied by the versatility of each stage. Each action or posture of these fish during this period is nothing but a demonstration of emotions and moods. Aquarists say that this spectacle must be seen at least once in a lifetime. Interesting, however, is the fact that for all its romanticism, this type of aquarium fish is famous for its fightingdisposition.
The second no less unique type of aquarium fish is the gourami. The mating process of gourami fish is quite amusing. During it, the male invites the female to the nest. When the female accepts the invitation, both individuals are located in this shelter. The male turns the female upside down and squeezes the eggs out of her. At the same time, he fertilizes them. When this process comes to an end, he releases the female, and then collects the eggs that have fallen to the bottom of the aquarium with his mouth and takes them to the nest.
