Improved Efficiency of Heat and Pressure Shocks for Producing Gynogenetic Rainbow Trout

Abstract

A large-scale investigation to identify effective procedures for the induction of gynogenesis in rainbow trout Oncorhynchus mykiss was conducted. Milt was effectively inactivated when diluted to a 10% concentration at depths of 0.33–0.65 mm and irradiated with 120–180 W/mm² (12,000–18,000 ergs/mm²) of ultraviolet light. Incubation temperature (8.8–14.6°C) had a marked effect on the effective postfertilization timing for first cleavage blockage induced by both hydrostatic pressure shock and heat shock and for pressure-induced second polar body retention but not for heat-induced second polar body retention. Higher temperature treatments of 29°C for 10 min and 31.5°C for 5 min were found to be more effective for first cleavage blockage than a treatment of 26°C for 20 min. Wide ranges of effective postfertilization timing adjusted to incubation temperature (°C-min) were identified for second polar body retention induced by heat shock (95–508 °C.min) and pressure shock (273–693 °C.min) and for first cleavage blockage induced by heat (981–2,616 °C.min) and pressure (2,730–3,696 °C-min). Gametes from 20 females from five strains were used to compare a 26°C heat shock lasting 20 min and applied 8 min postfertilization and a 62-MPa (9,000-lb/in²) pressure shock lasting 3 min and applied 38 min postfertilization. The gynogenesis efficacy was similar for the two treatments. A significant correlation (P < 0.001) was found between gynogenesis efficacy and gamete quality. Heat shock appears to be more practical than pressure shock for large-scale production of all-female stocks by gynogenesis. The implications of this study for triploid production are discussed.