Principles of Genetics and Breeding

Induction of triploidy in fishes

Triploidy is a process in which there will be addition of one set of chromosomes to the original diploid complement by preventing the extrusion of second polar body of the fertilized egg. Triploidy is induced by subjecting the fertilized egg by normal sperm to the usual shock treatments. Generally triploids are supposed to be sterile. Sterility is of great advantage in modern fish culture, as energy spent for maturation or gonadal development may possibly diverted or utilized for increased somatic growth, especially species like common carp and tilapia, which have shorter maturity cycle. Triploid common carp have shown more than 60% growth rate than its normal diploid counter part. Because of its sterility overpopulation is also checked, as the species has pond breeding habits similar to tilapias. Sterile triploid grass carp can be safely used for controlling aquatic weeds in open water system without fear of its establishment through reproduction.

Materials required

Matured male and female fishes, cotton, small screw cap tubes, petridish, ice blocks, water-bath, thermometer, quill feather, Hank's Balanced Salt Solution, etc.

Procedure

1. Inject spawning hormone such as ovaprim/ovatide to the brood fishes in the late evening hours.

2. Strip the milt from ripened males after allowing sufficient latency period (12 hrs)

3. Mix milt with freshly prepared Hank’s solution 1:4 without bicarbonate and store at 4°C for 1-6 hrs or until needed.

4. Strip the matured eggs as soon as ovulation commences.

5. Mix the stored milt (before mixing, the milt should be brought to water temperature) with freshly stripped eggs and fertilize the eggs by dry fertilization method.

6. Treat the fertilized eggs to cold shock (0°C for 1 hr) or heat shock (40°C for 1 or 2 min) immediately after fertilization before the release of second polar body.

7. After shock treatment bring the treated eggs to normal condition and incubate them.

8. Estimate the percentage of triploidy induction by preparing the chromosome spreads or by calculating the nuclear and cellular area and volume.