What is induced breeding of fishes?
The artificial process by means of which the extract of the pituitary is introduced inside the body of both the matured male and female fishes, then the carps after being excited lay eggs in the pond water and subsequently fertilization takes place and the process is called induced breeding of fishes. This process of breeding is also known as hypophysation.
Collection of Pituitary extract:
From the matured fishes of both sexes either belonging the same species as the recipient or a closely related the pituitary glands are collected. It is preferred to collect the pituitary gland from freshly killed fishes. But it has been observed that the pituitary glands taken from five to eight days old ice-preserved fishes have also given successful results. In the fish markets, where the head of the cut fishes are available the pituitary glands can be taken out from the posterior end of the cranium through the foramen magnum after cleaning the brain tissue.
Preparation of Pituitary extract:
For the induced breeding of fishes the preparation of pituitary extract is very important. But it is very easy to prepare. Immediate after the collection of the pituitary glands are kept in absolute alcohol for dehydration. After 24 hours, the alcohol is changed for further dehydration and defattening. The glands are then weighed and preserve in fresh alcohol in dark colored phials. It may be stored at room temperature or in a refrigerator. The weight of each pituitary gland varies from 7 to 19 mg in Rohu weighing 1kg to 3.8 kg and 3 to 23 mg in Mrigal weighing 0.3 to 3.6 kg. At the time of injection to carps for the induced breeding, the required quantity of pituitary glands are taken out of the phials and the alcohol is allowed to evaporate. The glands are then macerated with a tissue homogenizer either in distilled water or 0.3 percent of saline water. The gland suspension is then centrifuged and the supernatant fluid is drawn into a hypodermic syringe for the injection.
Method of injection and Spawning:
During the rainy season, the extract of the pituitary gland of the same species which is prepared on the above said scientific process is injected in the muscle of the matured carps, 1.5 kg the 5.5 kg weight in general. Just before evening, per one female with two males of the approximate same body weight are to be injected the pituitary extract by hypodermic syringe. Injection of the carps is to be done outside of the water lying on a piece of sponge which is used only to avoid the injury of the carps. In case of male carps the pituitary extracts are introduced once and in case of female carps it is introduced twice.
At first, at the rate of 2 to 3 mg of pituitary extract per kg of body weight is introduced in the muscle of the caudal peduncle or near the dorsal fin of the female carp. But in should be kept in mind that the injection should not be done on the lateral line sense organ of the carp. The needle of the syringe is to be introduced between the scales but with an angle of 45° with the body. After six hours of first injection, the second injection is given to the same female at the rate of 5 to 8 mg of pituitary extract per kg of body weight.
Then the carps, i.e., one female and two male are placed in a breeding hapa for spawning. Inside of the breeding hapa both the female and male carps are exited. After the excitation the female carps lays eggs. The eggs are externally fertilized by the spermatozoa that are discharged by the males. After that all the fishes are removed from the breeding hapa and then the eggs are collected by a net and are transferred to the inner part of the hatching hapa. After 14 to 18 hours, the spawns enter into the outer hapa and the induced breeding process completed. Then the spawns are collected from the outer hapa and transferred to the pond for nursery.
What are the advantages of induced breeding?
i) Eggs and spawns of carps at the collected from the river bed, there are every possibility of mixture of other fishes of eggs and spawns. Whereas, in the induced breeding there is no possibility of mixture and as a result the pure form of fish seeds are obtained. ii) Desired species of carps can be cultured through the induced breeding. iii) Large numbers of eggs are available from a fish through induced breeding. iv) In the same season, a carp can be induced to breed more than once. v) Transportation cost becomes very low as the carps can be breed in any desired pond. vi) Between the different species of fishes hybridization can be done and it is possible to get hybrid variety of fishes.