Tetraploid induction in Clarias gariepinus using cold shock protocol

Abstract

This study was aimed at optimizing the induction of tetraploid in African catfish Clarias gariepinus eggs using cold shock protocol. Three temperatures (0, 5, and 10 °C) were applied at three durations (2, 5, 10 min) to suppress the first mitotic cell division at about 1.4 τ0 after fertilization. Thereafter, the treatment and control groups were incubated at room temperature till the eggs were hatched and the performance characteristics of the progenies evaluated. The result obtained showed that the 0 and 10 °C respectively resulted in poor hatchability and low tetraploid percentage of the induced eggs. However, 5 °C cold shock for 2 or 5 min gave the highest hatchability (70%) and tetraploid percentage (35%); beyond this time, performance significantly reduces. The cytogenetically confirmed tetraploid progenies (4n = 112) in this study had higher erythrocyte axis length compared to their diploid counterparts (2n = 56). The exclusive tetraploid range of 12.5–17.4 μm and 10.2–14.1 μm was identified for the cell major and minor axis respectively, hence can be used to discriminate the progenies of the two ploidy groups. However, the progenies were similar in terms of morphological characterization and growth performance. It was concluded that 5 °C cold shock for 2–5 min at about 1.4 τ0 after fertilization is sufficient to induce reasonable percentages of tetraploids in C. gariepinus.