Induced Breeding Technique Of Fishes (Hypophysation)

Induced Breeding: Induced breeding is a technique used in aquaculture to stimulate the reproduction of fish in captivity. This is done by injecting the fish with hormones, which mimic the natural hormonal changes that occur during the spawning season.

Table of Contents

What is Induced Breeding

Induced breeding is a technique by which the economically important fishes (which generally do not breed in captive condition) are breed through artificial stimulation. Induced breeding is a technique whereby ripe fish breeders are stimulated by pituitary hormone or any other synthetic hormone introduction to breed in captive condition. It is also known as hypophysation.

History of Induced breeding

The technique of induced breeding was first evolved in Argentina after producing pituitary extract by Houssay 1930 where fish was injected with the hormone. In the year of 1934, Brazilians were succeeded in induced breeding by pituitary extract. This technique was also followed in America (Merlin & Hubs) and in Russia (Gerebilisky). In India first attempt of induced breeding was made by Khan in 1937 on Cirrhinus mrigala. Later in 1955 Dr. Hiralal Choudhuri applied this technique in minor carps (Esomus danricus, Pseudeotropius atherinoides). Ramaswamy and Sunderaraj first induced to breed Clarias batrachus & Heteropneustes fossilis. The first successful induced breeding on major carps was done by Dr. Hiralal Choudhuri 1957– Cirrhinus mrigala, C. reba, & Labeo rohita, Parameswaran & Alikuni successfully breed the exotic Chinese carps – Hypophthalmichthys molitrix & Ctenopharyngodon idella in 1963. ‘Induced Breeding Technique of fishes (Hypophysation)’

Why Induced Breeding is Necessary for Fish Culture

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.
Fish culture depends on the quality and availability of the seed of the fish. The supply of fish seed can only be ensured through induced breeding of the fish through hatcheries. Presently almost entire seed production of cultivable fishes is done through breeding in hatcheries.
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.

Why fishes 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.

Fish Pituitary gland

Pituitary gland is an endocrine gland situated on the ventral side of the brain
It is a small, soft, whitish body whose size and shape vary with species
It is more or less round in carps, oval in catla and rohu and pear shaped in mrigal
Pituitary is located in a concave cavity known as sella turcica and enclosed by a thin membrane known as durometer
It may be attached to the brain by a short stalk called the infundable stalk

Role of pituitary gland in Induced breeding

Pituitary glands secretes the gonadotrophins, ie; Follicle stimulating hormone (FSH) & Luteinizing hormone (LH)
FSH causes growth and maturation of ovarian follicle in females and spermatogenensis in the testis of males ‘Induced Breeding Technique of fishes (Hypophysation)’
LH causes luteinization in females and promote the production of testosterones in males

Induced Breeding Techniques

Removal of glands
Preservation of glands
Preparation of gland extract
Brooders selection
Injection to brooders
Spawning

1. Removal of glands

i) 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

ii) 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. ‘Induced Breeding Technique of fishes (Hypophysation)’

2. Preservation of Gland

Glands can be preserved in 100% ethyl alcohol Acetone can be used for preservation in temperate countries
Glycerin is also used as preservation media

Preservation of Pituitary Gland

3. Preparation of Gland Extract

Known amount of gland is taken by estimating the total quantity of fish to be breed.
Gland is dried in air by using blotting paper
Gland is taken in tissue homogenizer with little amount of distilled water
The dilution rate is 0.2 ml/kg of body weight of the fish
The pituitary extract is then centrifuged and only the supernatant solution is used for injection

Mortel and Pestle

Types of injections

Homoplastic injection: Injecting pituitary from one fish to another fish closely related to
the donor fish e.g. Carp pituitary gland extract to carps
Heteroplastic injection: Injecting pituitary from one fish to another fish distantly related
to the donor fish e.g. Carp pituitary gland extract to catfish and vice versa

Types of Dosage

4. Brooders Selection

The brooders must be healthy enough and ripe
Breeders should be collected in 1:2 ratio for female and male respectively
Fishes should be almost same size and weight
2 –4 years of age is generally selected
1 –5 kg body weight is preferable

Sexual Dimorphic Characters

5. Injection to the Brooders

The pituitary extract is administered into the body of breeders by means of hypodermic syringe either intra muscular or intra peritoneal
Determination of correct dosage of pituitary extract to be given to the breeders is very important and 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
The females receives 2 injections and the male receives only 1 injection (at the time of second injection to females) ‘Induced Breeding Technique of fishes (Hypophysation)’
I dose/ Provocative / Preliminary dosage & II dose / Effective / Resolving dosage
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 6 hrs 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.

6. Spawning

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 “Induced-Breeding”
The spawning takes place with in 3-6 hrs 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 fertilized eggs
The fertilized eggs are transparent, pearl like where as unfertilized eggs are opaque or whitish