Induced Diploid Gynogenesis in White Bass

Abstract

Abstract Optimal conditions were determined for induction of meiotic diploid gynogenesis in white bass Morone chrysops. In two series of experiments, ultraviolet light (UV) irradiation doses to inactivate sperm genome and optimal temperature shock to restore diploidy were established. Eggs of white bass were inseminated with sperm from striped bass M. saxatilis diluted (1:30) in saline and irradiated with UV at doses ranging from 50 to 1,200 J/m2. A typical “Hertwig effect” was observed with increasing UV dose. Larvae obtained at doses of 400 J/m2 and greater were abnormally developed (haploid syndrome) and had a haploid chromosome number (n = 24). Heat shocks to cause retention of the second polar body were applied. Heat shocks of 2-min duration at 36°C, 38°C, or 40°C were applied at 2 or 3 min after insemination to white bass eggs inseminated with irradiated (800 J/m2) striped bass sperm. The best results were obtained after application of 36°C heat shock at 3 min after insemination, which induced a significant increase in yield of diploid gynogens (24–39%, from initial numbers of gynogenetic embryos) and provided relatively high postshock embryo survival. The gynogenetic origin of diploids obtained was confirmed by the lack of melanophores in putative gynogens (contrary to pigmented control hybrid larvae).