EFFECTS OF ENVIRONMENTAL FACTORS ON SEX DETERMINATION IN FISH

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1) Temperature-sensitive periodGoldfish and barfin flounder exhibited a critical temperature-sensitive period. The end of the temperature-sensitive period was just before morphological sex differentiation. Moreover, to produce masculinized XX goldfish, it was needed to be kept in high temperatures throughout the temperature-sensitive period. While in order to produce a population where the genotypic and phenotypic sex coincide, it needed that fish are reared below 23℃ during the sensitive period without exact control of constant temperature.2) Histological changes in sex differentiation under the different rearing temperatureMasculinization of genetic female did not occur by low temperature treatment in goldfish. Ovarian differentiation was completely delayed at low temperature.3) Effects of various environmental factors on sex determinationIn goldfish, density and photoperiod have no effect on sex determination, although low pH treatment produced male-biased sex ratio while high pH treatment has no effect on masculinization. In contrast, high pH treatment led to masculinization in barfin flounder. In addition, cortisol treatment produced high male populations in goldfish, indicating a possibility of masculinization by environmental factors through stress responses.