Sex Reversal and Breeding of Grass Carp

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Abstract
Grass carp C. idella, 65-105 mm in total length, received a dimethylpolysiloxane implant containing 5 mg of 17 .alpha.-methyltestosterone (MT) or an injection of MT carried in liquid dimethylpolysiloxane. The implant masculinized the phenotypic sex of > 85% of larger (95-105 mm) females treated at age 10 wk. Only 27 of smaller (80-90 mm) females were sex-reversed when treatment started at age 10 wk, but over 95% of 80-90-mm-long females were masculinized when implanted at age 16 wk. Androgen administered in the liquid carrier masculinized < 6% of treated females. A sex-reversed (male) grass carp bred with an untreated female produced all-female progeny, based on histological examination of gonads. These results provide further evidence of female homogamety and suggest sex determination by a single heterologous pair of chromosomes in this species.