INITIAL FISH lifecycle
Attention to the processes contained in the early development of fish life is interesting because it deals with the stability of fish populations in some waters. Mortality in the early development of fish life is generally very large fluctuations in mortality which have major stakes in determining variations in the production of each year. However, this still requires digs further research to develop useful. Even more to the species of tropical fish, many that have not been disclosed.
Fish eggs with their parts.
Vertebrate eggs, according to the number of deutoplasma (egg yolk, etc.) contained in the cytoplasma, can be divided into two (Nelsen, 1953):
a. Eggs homolecithal (isolecithal).
This egg groups present only in mammal. Number of deutoplasma few bouts, especially in the form of grain-yolk fat and the largest in the cytoplasma.
b. Telolecithal eggs.
In the eggs of this group there are a number of egg yolks together in one poles. Ganoids fish eggs have the same kind of eggs that are not Amphibia-legged (Gymnophiona) where the number of relatively large yolk and gathered at one of poles. Romer (1955) called such groups of eggs mesolecithal name.
Eggs in Teleostei fish and massive Elasmobranchia deutoplasmanya. Protoplasm of these eggs will soon take part in some of the first division, are few. Egg yolks do not participate in the processes of cleavage, whereas embryo development is limited to that found in cytoplasma polar anima.
Ovipar fish eggs are not fertilized (Fig. 11), the exterior is coated by a membrane called a capsule or chorion membrane. Under another chorion.terdapat second membrane called the vitelline membrane. The third membrane surrounding the egg and the plasma membrane called the plasma membrane.
All three membranes are all stuck together and there is no space between them. Section contained egg cytoplasma usually gathered on the top of the egg poles called anima. Namely lower polar opposites on many egg yolks. These poles are called polar vegetative. Actually, the fish egg yolk is almost fills the entire cell volume. Egg yolk in the middle of the situation is more intense than the yellow egg on the edge because of the cytoplasma. Apart from that there are many in the cytoplasma around the egg nucleus. In chorion, there is a micropyle is a small hole where the entry of sperm into the egg at the time of conception.
If the new egg from the parent body and in contact with water one of two things will happen. First chorion membranes are released by vitelline membrane and form a space. This space is called the perivitelline space (Fig. 12). The entry of water into the eggs caused by pressure differences osmose and imbibisi protein found on the surface of the yolk. Vitelline membrane is a barrier to the entry of water should not seep into the egg.
The second process is hardening of the chorion membrane. The time required for hardening is not the same chorion membrane depends on Calcium ions contained in water. According to Hoar (1957) incubated eggs in water containing Calcium chlorida 0.0001 M, the membrane will chorionnya harder than the eggs that hatched in distilled water. This chorion hardening will prevent conception polyspermi. With the perivitelline space beneath the hardened chorion, the egg can move more freely during their development. The influence of waves against the position of the developing embryo is reduced because of the perivitelline space.
Conception
In the process of fertilization, spermatozoa enter the egg through the micropyle is present in chorion. Each spermatozoon has the same opportunity to fertilize an egg. However, because the room where the meeting of egg fertilization with spermatozoa in fish ovipar very large, the opportunity to meet the spermatozoon with the egg is actually very small.
To overcome these so successful fertilization, spermatozoa released a huge amount compared with the number of eggs to be fertilized. In the optimum condition the new fish spermatozoa released from the body has the power to move in water 1 - 2 minutes.
According to research done by Hartman and also by Motalenti (Hoar, 1957), eggs and sperm are released from the new parent body, issued a useful chemical in the process of fertilization. According to most of American literature, substances released by the egg and sperm are called Gamone. Gamone derived from egg is Gynamone I and II Gynamone. Gamone from spermatozoa is Androgamone I and II Androgamone. Gynamone I serve to accelerate the movement and attract spermatozoa from the same species are chemotaksis. Gynamone II is to collect and retain spermatozoa on the egg surface. I Androgamone function is to suppress the activity of spermatozoa while still in the genital tract of male fish. While Androgamone II is to create a soft surface charion as opposed to the function Gynamone II.
Egg layers in relative already in the water is hard and can not be penetrated by spermatozoa except through the micropyle shaped like a funnel. A large funnel hole located on the outside and a small hole on the inside. The hole was so small that could not be traversed by more than one sperm at a time. When the spermatozoon into the funnel hole, it is the plug for the rest, and after it entered the spermatozoon head, the tail off. Thus the general conception of the fish when it monosperma where one spermatozoon will go fast changes occurring in the micropyle.
Polyspermi If fertilization occurs, only one spermatozoon is merged together with the egg nucleus. Others are exploited by the egg as a food ingredient. Shortly after fertilization, the egg contents shrink slightly due to the outbreak of cavity contained alveoli in the egg. In the event more enlarged perivitelline cavity so that the fertilized egg can be a rotational movement during their development until they hatch.
Source: M. Ichsan Effendie, 1997
