Triploidy induction by electric shock in red hybrid tilapia

Abstract

The induction of triploidy in red hybrid tilapia (Oreochromis mossambicus × Oreochromis niloticus) using electric-shock at different duration (3, 5, 10, 15 and 20 min) is reported in this study. Triploidy induction was attempted by exposing fertilized egg to electric field maintained at 12 V at approximately 4 min after fertilization. The efficiency of triploidization was confirmed by counting the number of chromosomes and affirmed by assessing erythrocyte biometrics of one month old fingerlings. The result obtained shows that shock duration of 10 min was most effective as it induced triploidy in 87% of the fish in this group with a hatching rate of 68%. The chromosome count of induced triploids was 3n = 66 while diploid fish had 2n = 44. Also, many erythrocyte biometrics of the triploid hybrid tilapia were significantly larger than those of the diploid groups (between 12 and 56% increments). Out of all the erythrocyte parameters measured or calculated, the cell major axis had the highest percentage of erythrocytes (91.4%) that were within the exclusive triploid range (12.61–15.98 μm). Hence, despite the dominant oval shape of both diploid and triploid erythrocytes, discrimination of the entire fish groups was accurately done by solely accessing the exclusive range of the cell major axis. It was concluded that application of an electric field of 12 V for 10 mins was better for triploidization of the red hybrid tilapia eggs.