History of Induced breeding: The technique of induced breeding was first evolved in
Why Fish does not breed in Captivity??
Many cultural farm fishes like IMC do not breed in captivity. The reason may be environmental and consequently hormonal. Certain environmental parameters like photoperiods, rain, temperature, current of water influence the hormonal activity from pituitary and gonads. Disturbances arise in environment may cause the insufficient release of hormones in captive conditions and thus, the fish does not breed in captivity.
Other factors like poor foods or insufficient natural foods, exposure to biocides and other pollutants badly affect the maturation of ovary.
Why induced breeding is necessary??
The technique of induced breeding gives very promising result in fishery point of view due to –
· It gives pure spawn of certain species of fishes under cultivation. Spawn collected from natural water is not pure as because some undesirable wild species may come with them in culture pond. Sorting of pure seed is quite impossible in those stages. In later stages it is possible, but time consuming.
· It assures timely available of pure seed, where as in nature the availability of seed is quite uncertain.
· It can fulfill any quantity of demand in any time.
· It also cuts short the holding potential spawners over long periods in uncertain hope of their breeding in time. Many carps take their full maturity in confined water but do not breed.
· The technique is very simple and does not need too much technical assistance or knowledge. It can be easily learnt by a layman without much training.
· The cost of expenditure is very low than the natural collections of spawns.
Technique of Induced breeding:
Preparation of Pituitary Extract – For preparation of gland extract the glands are removed carefully from freshly killed fish called donor fish. For best result the donor fish should be fully ripe and mature. Common carp is the best donor fish, because it breeds through out the year and the individuals are available in all parts of the world. The pituitary glands of such species are relatively large. The gland should be collected prior to spawning. However the gland doesn’t show species specificity and any carp species can be used as donor. However the glands of relative or closely related species show best result.
Removal of Glands –
The removal of glands can be done by following two processes:
- Removal through foramen magnum – the foramen magnum was first exposed by removing vertebral parts adhering to skull. Fat is removed first by means of forceps and then cotton piece. A pair of forceps then inserted into foramen magnum dorsally to the brain and anterior part of the brain now detached and remaining is carefully lifted out through the foramen magnum. The gland is then located and removed.
- Removal of gland by dissecting head – This technique is not used commercially as because the heads are damaged by this process. The first method of removal is less time consuming and economical as the heads are used for human consumptions later. At first the head is dissected using sharp butcher’s knife, a portion of scalp is chopped off in a clean cut with one stroke. Fat surrounding the brain is removed with the help of cotton. Olfactory and optic nerves are now severed, and then brain is lifted up and removed. Locate the gland. The gland may come up along with the brain or may remain behind on the floor of brain cavity often covered with a membrane. In any case the gland is carefully removed after separating it from membrane or the brain proper. The gland must not be damaged or torn.
The gland after removal needs to be preserved for certain periods or for future use. The glands are taken in absolute alcohol and can be stored in room temperature. In certain countries like
Preparation of Pituitary Extract:
The preserved glands of known quantity are taken out and macerated in a homogenizer after evaporation of alcohol with little amount of distilled water. Then the extract is freed of suspended particles by means of centrifugation. It is the diluted with required amount of distilled water or 0.3% saline water or a suitable physiological solution. The extract is now ready for use.
Istruments for Gland Extract Preparation Removal of Pituitary Gland
Preservation of Extract:
The extract can also be preserved for future use. In this process in place of saline water glycerine is used and extract can be preserved in room temperature or in refrigerator. Other methods of preservation are done by propane and trichloro-acetic acid in place of glycerine.
Selection of Brooders:
Proper selection of are the key of success in case of induced breeding. The breeders should be healthy, fully ripe and of medium sized. They should preferably come into the age group ranging from 2 – 4yrs and have the weight of 1 – 5kgs. Large sized breeders are avoided for difficulty in handling. For ripe male and female carps, it can be easily identified. The male shows roughness on pectoral fins when belly pressed milt freely oozes out. The ripe female shows relatively smooth pectoral fins and operculum. The eggs are released when the belly is pressed smoothly in female. The belly of ripe female is generally soft and round or budged. The vent is swollen, protruding and pinkish in colour. It is wiser to practice to keep ready adequate stock of potential brooders. For this a few months before breeding season potential breeders are kept away under care, and fed on supplementary feed (rice bran and oil cake mixture).
Injection to the breeders:
The pituitary extract is administered into the body of breeders by means of hypodermic syringe either intra muscular or intra peritoneal. To ensure a higher percentage of fertilisation during induced spawning it is necessary that there is synchronisation between ovulation and milt shading. This difficult to achieve with a set of breeders having one male and one female. Therefore the common practice is to use a set consisting of one female and two males.
Determination of correct dosage of pituitary extract to be given to the breeders is very important though a difficult matter. Dosage depends upon the size and state of maturity of the recipient (breeders) as well as upon the state of maturity of the donor for the glands. It has been found that the potency of the gland is influenced by the size, the age, the sex, the state of sexual maturity of the donor fish as also the size of the gland itself. Great difficulty is encountered because it is not easy matter to ascertain the state of maturity of fish from external examination. Usually the female is given a preliminary dose of 2-3mg/kg of body wt. The preliminary dose is not given to the male. After an interval of time about 6hrs a second dose of 5 – 8mg are given per kg of body wt of female. The male was given then the first dose of injection with female @ 2-3mg/kg of body wt. The dose may be depending upon the maturity of fish, age, sex and also the environmental conditions.
For intra muscular injection the fish is laid on its side while held in hand net and the needle is inserted either in the caudal peduncle or in the shoulder. For intra peritoneal the injections are given in the bases of paired pectoral fins. But it is avoided because less expert hand can puncture heard of the fish.
After injection to the brooders a set of brooders are released into breeding hapa. In hapa breeding the hapa is the fine netting, rectangular in shape and is held by four bamboo poles one at each corner. Closed meshed mosquito netting is preferred for that purpose, as its meshes will allow a good circulation of water and will also not let the laid eggs and milt escape through the meshes. The hapa measures the range of 3m × 1.5m × 1m for breeders weighing to 3 to 5kgs. The height of the hapa should remain about 20cm above to the level of water. The roof can be open or closed. The roof can be opened or closed.
The spawning takes place with in 3-6hrs following the second dose. It turns out the midnight if the second injection was given in the evening. Successful induced breeding results in the spawn of fertilised eggs. The fertilised eggs are transparent, pearl like where as unfertilised eggs are opaque or whitish.
Factors influencing the breeding:
Climate - 24°C to 31°C with cloudy days and rainy periods. Light drizzling following heavy rains is ideal. In absence of rain artificial showers are used.
Water – Flowing water is preferred.
Turbidity – 100ppm 1000ppm.
Light – It is known to bring that light may help in early maturation and spawning of fish.