Triploidy is the result of producing an organism with three sets of chromosomes (3n). Induction of triploidy requires the application of physical shocks (temperature, pressure and chemical) during meiotic cell division leading to the retention of the second polar body (3n chromosomes). Triploid offspring can also be obtained by the combination of gametes from a diploid and tetraploid parent. Previous studies suggested that triploid Zebrafish are male-biased and sterile due to abnormal gonad development. We aimed to evaluate the fertility of triploid Zebrafish by crossing triploid individuals with another triploid (3n x 3n) and with diploids (3n x 2n), to address the contradictory information about triploid fertility. Cold shock (4?) was applied at 3 minutes post fertilization for 20 minutes to produce triploid Zebrafish. Ninety percent of offspring were confirmed triploid at six days post fertilization (dpf) by flow cytometry analysis. Fish were grown out to sexual maturity and sex ratio was determined. At 90 dpf, 12% of triploid offspring were determined to be females. Among those triploid females (n=6), two produced offspring by sibling-crossing (3n*3n) and back-crossing (3n*2n) in six trials.
Triploid females produced eggs when spawned with diploid males in all trials except one (Table 1). All larvae were found to be aneuploid (C-value = 2.24 ± 0.07 pg) by flow cytometry analysis at 6 dpf and no larvae survived more than 10 dpf. Sibling-crossing of triploid male and triploid female produced a comparatively smaller number of eggs, and very few were fertilized (Table 1).