Temperature effects and genotype-temperature interactions on sex determination in the European sea bass (Dicentrarchus labrax L.).

The effect of temperature on sex-ratios in 27 families of sea bass reared in the same tank from the fertilization stage onward was investigated. An excess of males (68%) was found in the groups that were reared at high temperature (mean +/- standard deviation: 20+/-1 degrees C) until they reached the mean size of 8.1 cm (Standard Length, 149 days post-fertilization [p.f.]). Masculinization was higher (89% of males) in the groups maintained at low temperature (13 degrees C), from fertilization to a mean length of 6.5 cm (346 days p.f.). Shifts from high to low temperature at 8.1cm and from low to high temperature at 6.5 cm had no consequence on the sex-ratio. The percentage of males showing intratesticular oocytes was higher at low temperature (63%) than at high temperature (36%), suggesting that these males may be sensitive fish that have been masculinized by environmental factors. Fish sampled in the groups reared at high (2,200 fish) and low (500 fish) temperature were genotyped on three microsatellite loci. This allowed them to be assigned to the breeders used in the crossing design, thus permitting an analysis of parental influence on sex-ratios. In groups reared at high temperature, both parents had a significant additive effect on the percentage of females, and the interaction between sire and dam was not significant. Genotype temperature interactions were also detected and their existence suggests the interesting possibility of selecting nonsensitive genotypes in breeding programs.