Temperature-Sensitive Period of Sex Determination in the Atlantic Silverside, Menidia menidia

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Abstract
We investigated the timing and duration of the temperature-sensitive period of development in the Atlantic silverside, Menidia menidia, by measuring the sex ratio in groups of larvae shifted reciprocally among low and high temperatures as development progressed. The sensitive period of sex determination was dependent on body size, rather than age, and occurred during the middle to later stages of larval development when fish were between 8 and 21 mm in total length. Sex determination was irreversibly fixed earlier in development (i.e. at 15 mm in length) at higher than at lower temperatures. Higher, male-producing temperatures therefore appear to more strongly effect sex determination than do lower, female-producing temperatures. Temperature prior to, or after, the sensitive period had no measurable effect on sex ratio. From histological examination we suggest that gonad differentiation coincided with the end of the temperature-sensitive period. The timing and duration of the temperature-sensitive period in M. menidia is generally similar to the hormone-sensitive period identified in other fishes. Both phenomena reveal a specific developmental period during which the course of primary sex differentiation in fishes is labile.