Studies On The Artificial Induction Of Polyploidy In Yellow Catfish (Pelteobagrus Fulvidraco)

The yellow catfish Pelteobagrus fulvidraco, one of the commercial freshwater species in China, with tender flesh, delicious taste, high value of nutritional, has been widely cultured in our country due to the success of artificial propagation in 2000s. However, sexual maturation occurs usually less than one years old yellow catfish under culture conditions, before commercial size is reached. This is considered a major problem because sexual maturation is accompanied by a decrease in growth rate and flesh quality. In order to improve the breeding benefit and accelerate the growth rate of yellow catfish, we need to delay puberty or permanently inhibiting gonad development of yellow catfish as far as possible. A solution to this problem may be found in the production of triploid fish that are functionally sterile from the odd number of chromosomes that cause disruption of meiosis in the gametes. In present study, several shock methods such as cold shock, heat shock and pressure shock are used to induce triploidy and tetraploidy in yellow catfish during last May to August. The main results are summarized as follows:(1) The optimal conditions for triploidy yellow catfish induction were investigated by altering the timing, and the intensity and duration of application of cold, heat and pressure shocks and the efficiency of three methods were also compared. The results shows:①The triploidy yellow catfish could be obtained by cold, heat and hydrostatic pressure shock and triploid rates in experimental groups were mainly affected by the timing, intensity and duration of shocks. In July, at the fertilization temperature of 25℃, treatment optimal for cold shock was 4℃for 10min at 3min after fertilization with 58% triploid embryos at gastrul stage and 53%viable fry to control at hatching; and for heat shock was 40.5℃for 2min at 2min after fertilization with 59% triploid embryos at gastrul stage and 36% viable fry to control at hatching; and for pressure shock was 550kg/cm2 for 3min at 3min after fertilization with 55% triploid embryos at gastrul stage and 54% viable fry to control at hatching.②Comparing the rate of triploid at gastrul stage, the rate of viable fry to control, and the rate of triploid at adulthood synthetically, it is suggested that the efficiency of pressure shock was much higher than the other two methods. Cold shock and heat shock resulted in more or less the same effect, but both have their respective merits. Cold shock has a relatively high rate of viable fry to control, and heat shock has a relatively high rate of triploid at adulthood.(2) Orthogonal composite designs were used in experiments. Eggs were hand-stripped and fertilized artificially. First division was visible and occurred about 57min after fertilization. Zygotes were developed in freshwater at 25℃. Using heat shock treatment for blocking first division of fertilized eggs, tetraploidy were indued by application of 39,40 and 41℃heat shocks to eggs for 1,1.5 and 2min at 42,45,48,51, 54 and 57min AF in yellow catfish. The results showed that the tetraploid rates of embryos were range from 0%to 42.11%, and the viable fry rates to control were were range from 0%to50.57%. The suitable factors of heat shock treatments for inducing tetraploid in yellow catfish were 40±0.2℃for 1.5-1.8min at 45 or 54min AF.(3) A heat shock of 40.5℃for 2min that was suitable for triploidy produced was applied to induce tetraploidy at 42-58min AF. The results showed that the tetraploid rates of embryos at gastrul stage were range from 10.61%to 62.16%, and the tetraploid rates of embryos at hatching stage were range from 11%to 75%, and the viable fry rates to control were range from 9.77%to 36.05%. Shocks applied at 44min and 54min AF resulted in the highest tepraploid rates of embryos in all of the treatment groups.(4) In fish, the high quality mitotic chromosome made from embryos is widely applied in the study of polyploid breeding, hybrid Breeding, karyotype analysis and sex control. It is disadvantage to use conventional preparation for chromosome methods in experiment due to taking a very long time, having fussy steps and lacking stability. In this paper, a rapid, simple and stable method for obtaining permanent chromosome preparation from embryos of fish was established by improving the conventional method.