Comparative studies in the induction of triploidy for <I>Pelteobagrus fulvidraco</I> by cold and heat shocks

Abstract

The yellow catfish Pelteobagrus fulvidraco has become a valuable aquaculture species in China and the possible use of sterile triploids is an interesting option for its culture. The optimal conditions for the induction of triploidy for P. fulvidraco by means of cold and heat shocks were investigated and compared in the present study. Three treatment variables were considered: the time after fertilization when the shock was applied,the temperature and the duration of the shock. Ploidy was determined by chromosome counting and flow cytometric analysis. The diploid,triploid,haploid and aneuploid (or heteroploid) were all identified in the P. fulvidraco eggs (or juvenile individuals) after cold and heat shocks. The survival rate in stages of gastrulae and post hatch,the rates of triploidy induction and deformity under different treatment methods were evaluated. The results indicated that optimal treatment conditions for cold shocks were 5 ℃ for 20 min at 2 min after fertilization,which resulted in about 70% triploidy embryos,50% relative survival at hatching stage,and 25% triploidy individuals in juvenile period. The optimal treatment conditions for heat shocks were 40 ℃ for 2 min at 2 min after fertilization,which results in 58% triploidy embryos,39% relative survival at hatching stage,and 40% triploidy individuals in juvenile period. The orthogonal design analysis showed that the time after fertilization when the shock was applied was the most important factor to the rates of hatching and triploid induction at embryonic stage in cold-shock groups,while in heat-shock groups temperature was the most important factor to the inducing rates of triploids,deformities and relative survival at hatching stage. The results demonstrated that cold shock was less effective in inducing triploidy in P. fulvidraco for its serious injury to embryos and lower survival rate after hatching compared with heat shock. In conclusion,this paper presents the optimal conditions for triploidy induction in P. fulvidraco using cold and heat shocks and indicates that it is possible to mass-produce triploids of this commercially important species.