Effect of rearing temperatures post hatching on sex ratios of rainbow trout (Oncorhynchus mykiss) populations

Abstract A comprehensive experiment was carried out to study the effect of an elevated temperature of 18 °C for 30 days (starting on day 42 post fertilization) on sex ratios in progenies of six different (I, II, III, IV, V and VI) rainbow trout broodstocks of the Experimental Trout Farm Relliehausen (University of Goettingen, Germany). Further, the repeatability of the obtained results and the effects of mating partners on temperature responsiveness were examined. In total about 7000 temperature-treated (18 °C) fish and their corresponding 7000 full sibs kept at 12 °C were sexed. In general, the mean survival rates after temperature treatment of 18 °C did not differ significantly from the corresponding values of the full sibs kept at 12 °C. Significant differences to 18 °C temperature responsiveness were observed between the progenies of the six broodstock populations. Broodstock population II showed the highest mean female percentage of 60.6% of the temperature-treated progenies, while population III showed the lowest mean female percentage of 36.0%. Single pair matings within the four (I, III, V and VI) populations were repeated and the percentage of females in the 18 °C-treated replicated spawns differed only by 0.4%–5.8%. In addition, paternal and maternal half sibs showed that the sensitivity of sex ratios to temperature treatment varied between breeding pairs. Both parents, male and female, seem to contribute to the different sex ratios after treatment. It was concluded that a sensitivity of sex-differentiation to temperature treatments seems to exist in rainbow trout depending on the genotype and the applied temperature treatment.