Field protocol for induction of triploidy in Clarias gariepinus
A simple field protocol for induction of triploidy in Clarias gariepinus using cold shock was developed. The quantity of ice needed to bring temperature of water down to desired temperature was first calculated. Fertilized eggs were then exposed to 5 ºC or 10 ºC at different times. Percentage hatchability for 5 ºC fertilized cold-shocked eggs was 55.63%, 49.53% and 46.76% for 10, 20 and 35 minutes accordingly. At 10 ºC cold shock hatchability was 53.23%, 46.85% and 48.24% for 10, 20 and 35 minutes accordingly while 84.28% hatchability was achieved in control. A total of 12 larvae from each treatment tested for triploidy by counting number of chromosomes in 8-hydroxyquinolin-arrested metaphase spreads from newly-hatched larvae. All individual larvae exposed to cold shock showed 3n chromosomes. No triploid was found in control group. Results revealed that 100% triploidy could be successfully induced in C. gariepinus by cold shock for 10 minutes duration. One-way Analysis of Variance showed that treatment 10 ºC at 10 minutes duration produced higher mean weight gain (35.94±0.96 g), followed by treatment 5 ºC at 10 minutes duration whose value was 32.41±1.35 g but there was no significant difference. However, control (51.28±4.82 g) was significantly heavier than triploids.
Keywords: Triploidy, biotechnology, sterile, hatchability, Clarias garipinus