Induced gynogenesis in the silver barb ( Puntius gonionotus Bleeker) and evidence for female homogamety

Abstract

Diploid gynogenesis was induced experimentally in the silver barb ( Puntius gonionotus) as the first step in a programme aimed at monosex female production. Sperm was exposed to ultraviolet light at a dose rate of 196 μWcm −2 for 0–32 min (0–376.3 mJcm −2), using a standard sperm concentration of 8 × 10 8ml −1. The optimal UV dose for producing haploid gynogenetics when such irradiated sperm was used to fertilise eggs was 1 min (11.8 mJcm −2). Diploidisation of the gynogenetic genome was achieved via temperature shocks. Cold shocks of 2 ± 0.1 °C for 10, 20 or 30 min or a heat shock of 40 ± 0.1 °C for 1.0 min were applied at various times after fertilisation (pre-shock incubation temperature 29 ± 1 °C). A maximum survival rate of 61.3% viable diploid gynogenetic offspring (relative to control) was obtained using a cold shock of 2 ± 0.1 °C for 10 min starting 1.5 min after fertilisation. A total of 268 diploid gynogenetic fry from ten different females were reared and sexed by histological examination of the gonads. With the exception of four undifferentiated fish, all of the gynogenetic fish were female, in contrast to the controls, which had a mean sex ratio of 54.6% female (which was not significantly different from 50% female). The implications of these results for monosex female production are discussed.