Optimization of Thermal Shock Protocols for Induction of Triploidy in Brook Trout

Abstract

Techniques for production of triploids are well described for commercially reared salmonids (e.g., rainbow trout Oncorhynchus mykiss and Atlantic salmon Salmo salar). Among less commonly used species, including brook trout Salvelinus fontinalis, these protocols have not been optimized. As a prelude to investigating the regional potential for commercial culture of brook trout with all-female and all-female triploid stocks, we conducted experiments to test the effects of the primary variables of thermal shock used to induce retention of second polar bodies. The objective was to identify a protocol that maximizes yield of both triploid and gynogenetic diploid progeny. The first experiment measured survival of gynogenetic embryos produced by heat shocks involving combinations of different temperatures (26, 27, 28, or 29°C) and durations (7, 10, 13, 16, 19, or 22 min). In three subsequent experiments, production of triploids was assessed for thermal shocks involving variable times of initiation (7, 10, 13, 16, 19, or 22 min postactivation) in addition to the above temperatures and durations. Significant trends for decrease in survival and increase in percent triploidy were observed with increase in temperature and duration of thermal shock. Effects for time of initiation in two of three experiments were nonsignificant; in the third, survival tended to increase and percent triploidy to decrease with increase in time of initiation. With a preshock incubation temperature of 11–12°C, the most generally effective protocol involved a thermal shock of 28°C for 10 min duration initiated at 10–16 min postactivation, for which relative survival was 68–71%, percent triploidy was 79–99%, and triploid yield was 54–70%. In a fifth experiment, the fertilized eggs of 14 females were treated separately with a 28°C shock of 10 min applied at 10 min postactivation. Although relative survival to initiation of feeding ranged between 42% and 100%, percent triploidy was consistently 98–100%.