Stages of embryonic development of fish
There is no doubt that the embryonic development of fish is as fabulous as that of any other animal. The processes that are carried out to form a new life are fascinating. In this article we will tell you how a fish is formed. It's really interesting!
Embryonic development: general concepts
Before talking about the embryonic development of fish, it would be good to learn a little about embryology in general.
For starters, there are different types of eggs, depending on the organization of the yolk inside. They can be isoleciths (as in mammals), centrolecitos (arthropods) and telolecitos (mollusks, fish, reptiles). , birds or amphibians). In any case, there are three phases within embryonic development, which are the following:
Cell divisions occur and end in a state called blastula.
Cells rearrange and give rise to blastoderms.
3. Differentiation and organogenesis
The tissues and organs are formed, which fix the structure of the new individual to be developed.
In addition, we can not leave aside what happens with the temperature, fundamental in the embryonic development of fish, but also of other animal species. Eggs are more likely to end their cycle - that is, hatchlings - if the ambient temperature does not change more than 8 ° C.
When this does not happen and they go through extreme temperatures, there is less chance of hatching and more likely that offspring are born with serious anomalies or do not survive the first hours.
How is the embryonic development of the fish?
Now that we know the basic notions of embryology, we will briefly explain what are the different stages through which an embryo of fish passes in an egg telolecito before birth:
1. Zygotic phase
Once the egg is fertilized by the male, it remains in a zygote state until the first division occurs . How long does this process take? Everything will depend on the species and the temperature of the waters. For example, the zebrafish needs 40 minutes to perform the first segmentation after fertilization.
Although it can be thought that in the zygotic phase there are no changes, the truth is that inside the egg there are many processes that will subsequently lead to the birth of a new life.
2. Segmentation phase
It begins when the first division of the zygote occurs and is a meroblastic segmentation. This happens because the eggs of the fish have a yolk that limits the area where it can be develop the embryo. Therefore, it has a reduced space to be segmented.
The divisions -both vertical and horizontal- are fast and synchronized, which results in the discoidal blastula, a 'mound' of cells within of the yolk.
3. Gastric phase
In this third phase a rearrangement of the cells takes place through morphogenetic movements (so that they all have the same information). In the embryonic development of the fish this stage is known as involution.
This phase is characterized by a reduction in the rate of cell division and a null growth. Likewise, many interesting things happen, because For example, the endoderm, the ectoderm and the discogástrula are formed, all cellular layers.
4.For example, in this stage of differentiation, the cephalic (brain), optic (eyes) and blastopore (anus) vesicles appear.
Little by little, the bones of the spine, muscles and muscles will also form. the other organs: epidermis, dermis, nervous system, digestive tract, reproductive organs, circulatory system, etc.
Once the individual is perfectly formed, it is the moment of hatching, the final stage of embryonic development in the fish. When they are born, they already have the same shape as when they are adults, but in small size. As if they were an exact copy of their parents!