YY super sperm lead to all male triploids and tetraploids

Androgenesis is a unique and rarely encountered reproductive mode in which the offspring only inherit the paternal nuclear genome, resulting in relatively few viable individuals.

In this study, a super male (YY) crucian carp was obtained by androgenesis with the diploid sperm of autotetraploid crucian carp (4n = 200). Flow cytometry assay confirmed the fish was diploid. The scanning electron microscopy and flow cytometry analysis results of sperm revealed that the YY crucian carp produced unreduced diploid sperm. To prove the special reproductive characteristic and homozygosity of the YY crucian carp, three rounds of hybridization experiments were performed. First, self-crossing between female androgenic progenies and YY crucian carp generated all male tetraploids. Then, hybridization of female red crucian carp (2n = 100) and female autotetraploid fish (4n = 200) with YY crucian carp produced all male triploids and all male tetraploids, respectively.

This is the first time reported producing a viable diploid homozygous YY fish with unreduced diploid sperm of the autotetraploid fish, which were derived from distant hybridization. These results will not only help explaining the sex determination mechanism in teleost fish, but also play a significant role in genetic breeding in aquaculture.