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Juvenile growth and gonadal development in sex reversed female chinook salmon Gorkhali, Neena Amatya


In salmon farming, the culture of all female fish avoids the problem of precocial males and reduces the costs of production. In an all female monosex population, hormonal (17α-methyltestosterone, MT) masculinization can be used to obtain XX (chromosome) males for breeding purposes. Such treatment has been successful in chinook salmon. As adults, these XX males produced viable sperm and were fully functional. The present investigation compares the juvenile growth and gonadal development of normal XY male, female, and sex-reversed XX male chinook salmon. Ten monosex families and 10 normal families (from two farm sources) were used for comparison. In each monosex family, half of the fish were exposed to MT treatment and were raised with equal number of untreated fish in a family tank. The body weight and fork length measurements from 940 parr (4 months of age) and 884 pre-smolt (7 months of age) fish were examined. There were no significant differences in parr weight, specific growth rate, and presmolt weight between MT-treated fish and non-treated fish, nor between males and females, but there were significant differences in the growth rate and fork length between the stocks from the two farm sources. Precocial males have been found at the pre-smolt stage age and have not been reported previously. There was no indication that measurements taken from MT-treated fish may bias Breeding Value estimates derived from these measurements, but continued monitoring in the next few generations may be necessary to study the relationship between selection for fast growth rate and the incidence of early precocial development in MT-treated fish. Sex was determined by histological examination of the gonads in 159 parrs and 125 presmolts. Forty three percent of monosex family fish were intersex at parr stage and 19% at presmolt stage. The particular MT treatment protocol adopted by the fish farms may have caused transitional intersexuality in the treated fish. It would be necessary to compare different MT treatment protocols and to examine fish of different stocks to determine the source of variation. These findings suggest that the use of MT-treatment to produce XX males may not have any adverse effect on a selective breeding program.

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