Attempted triploid induction in Atlantic salmon ( Salmo salar) using cold shocks

Abstract

Radiation gynogenesis was used to investigate the effect of sub-zero cold shocks in inhibiting the second meiotic division of eggs of Atlantic salmon ( Salmo salar). If cold shocks were successful in giving rise to diploid gynogenesis they could be used to produce triploids from eggs fertilized with non-irradiated spermatozoa. Different concentrations of saline and glycerol solution were used to depress the freezing point of water, enabling eggs to be cold-shocked at temperatures below 0°C. Control experiments using eggs fertilized with unirradiated spermatozoa were made to assess the effect of saline and glycerol on normal egg development. A 4 h immersion in saline solution following dry fertilization was lethal to eggs, and haploid development was observed in some experiments when eggs were pre-treated for short periods in fresh water before immersion in saline. No such anomalies in development were observed using glycerol. Eggs fertilized with sperm receiving 60Co γ-irradiation at a dose of 10 5 rad were cold-shocked at between −0.2 and −1.7°C, at varying time intervals up to 40 min after fertilization, for a duration of 4 h. No treatments were particularly successful in inducing diploid gynogenesis. These findings are discussed in relation to studies in which cold shocks are highly successful in inducing diploid gynogenesis and triploidy in eggs of plaice ( Pleuronectes platessa).