Induced Gynogenesis in Black Crappie

Abstract

This study reports the results of initial experiments on induced diploid gynogenesis in black crappie Pomoxis nigromaculatus. White bass Morone chrysops were an effective sperm donor for gynogenetic experiments with black crappies. White bass spermatozoa fertilized black crappie eggs, but hybrid larvae were not viable and died after hatching. In a series of experiments, we determined the ultraviolet (UV) light dose required to inactivate the sperm genome and the heat shock parameters needed to restore diploidy. Black crappie eggs were inseminated with white bass sperm irradiated with UV dosages ranging from 25 to 2,500 J/m2. A typical “Hertwig effect” in the yield of hatched larvae was observed with dosages greater than 100 J/m2. The genetic inactivation of paternal chromosomes was confirmed by flow cytometry measurement of DNA content in larval cells. Larvae resulting from sperm irradiated at a dose of 1,000 J/m2 were haploid. Time durations of mitotic interval (τ0) at different temperatures for black crappies have been determined to standardize data on heat shock timing in experiments with different preshock temperatures. The resultant regression equation (τ0 = 70.96-2.32T, where T is water temperature) was used for calculation of the value of τ0 for any water temperature observed in the experiments. Application of heat shock was effective for suppression of the second meiotic division in eggs and resulted in morphologically normal diploid gynogenetic larvae. The effectiveness of shock was dependent on its parameters. The best yield of diploid gynogens (8.3% from the initial number of eggs) was observed after application of 37°C shock and 1.5-min duration at 0.05 τ0 after insemination. Future experiments will be directed to increase the effectiveness of heat shock by further optimization of its parameters.