Induced Breeding

The induced breeding technique includes stimulating mature brood fish to spawn under artificial environment through administration of hormone and manipulation of environmental conditions.

Hypophysation:

• The technique of inducing fish to spawn by administering pituitary gland extract is known as the hypophysation technique.
• The process of hypophysation involves different steps and needs technical expertise for perfection of the breeding operation.

Selection of Brooders

The success of induced breeding depends on the proper selection of brooders. The identification of the sex is made on the basis of the external characters.

• The mature males are distinguished from the females by the presence of denticulation on the dorsal surface of the pectoral fin which is hard and rough to touch.
• In males the abdomen is comparatively flat and the vent is not swollen but they ooze milt (whitish sexual product) at slight pressure on their abdomen (Fig. 1).

The ripe females have soft and smooth pectoral fins and bulging abdomen with swollen pinkish genital opening (Fig. 2).

Recommended weight and age for selection of brood fish

The mature male and female brooders are segregated and stocked sex-wise in separate ponds about 1-2 months prior to the breeding operation for optimizing spawning and their health and maturity status should be monitored periodically.

The mature male and female brooders are segregated and stocked sex-wise in separate ponds about 1-2 months prior to the breeding operation for optimizing spawning and their health and maturity status should be monitored periodically.

• During breeding season, fully ripe male and gravid females are netted out carefully and after selection they are carried to the hatchery site for breeding.
• For long distance transport, polythene bag or PVC pillow or crates with provisions for oxygenation are recommended. However, for short distance, canvas bag filled with water or big sized container with water may be used.
• At the hatchery site, the brood fishes are kept in breeding hapa fixed either in conditioning pool with inlet-outlet facility or in breeding pool of hatcheries filled with water for about 5-6 hours. This is done for conditioning of the brooders before the actual process of hormone administration. Feeding should not be done.
• Fresh water should be sprinkled with the help of shower for oxygenation during the process of conditioning. After proper conditioning the individual brood fish is weighed using a spring balance. The brooders are then ready to receive injection. Hand nets or scoop nets are generally used during weighing and injecting process.

Determination of dosage for injection

• Dosages of pituitary gland extract are calculated on the basis of body weight of the recipient fish.
• Besides body weight, determination of proper dosages of pituitary gland depends largely on the stage of sexual maturity of the brooders and also to some extent on the environmental conditions.
• The female brood fish is administered with 2 doses of pituitary hormone at an interval of 6 hrs.
• The male fish is given only a single dose of hormone at the time of 2nd dose to the female. The dose of hormone to be used for both the male and female is given below-

Process for administration of hormone

• The selected brood fishes are injected intra-muscularly at the caudal peduncle or the space between caudal peduncle and dorsal fin above the lateral line. The intra peritoneal injection at the base of pectoral fin is also practiced. Never inject on the lateral line.
• A 2ml capacity hypodermic syringe with 0.1ml graduation preferably with inter locking system is most convenient for injecting most of the fishes.
• The size of the needle depends upon the size of the brooder to be injected. Usually with increase in weight and length of fish, the specification number of the needle proportionately decreases.
• Generally B.D.H. No. 22 needle is used for fishes weighing between 1 to 3 kg and No. 19 for the larger ones.
• For smaller fishes with less than 1 kg weight, No. 24 needle is considered.
• Careful handling of brooder fish during the injection process is very important so that there is no physical strain or injury to the brooder.
• Usually the recipient fish is taken out from the conditioning enclosure by hand net or scoop net and are carefully placed on a rubber cushion of suitable size. Before taking out the fish, the syringe is filled with required quantity of hormone.
• The piston of the syringe is hold firmly by placing the thumb finger on the head of the piston and the other fingers in suitable positions of the graduated cylinder of the syringe.
• Before inserting the syringe one person places his hand on the head of the fish and the person giving injection holds the caudal peduncle and inserts the needle at 45º angle and injects the fluid with thumb finger pressing the head of the piston.

Breeding season:

• In Assam, generally the time sequence of induce breeding starts in April. It is started with silver carp and grass carp in April, followed by catla, rohu and mrigal. But there is no hard and fast rule of that breeding sequence.