Sex reversal in salmonid culture

Abstract

Oral administration of 17β-oestradiol, at a concentration of 20 mg/kg diet, to juvenile rainbow trout and Atlantic salmon, maintained under the natureal photoperiod, for minimum respective periods of 0–30 and 0–21 days following first feeding, induced sex reversal among the males, and resulted in all-female stocks whose gonads were histologically indistinguishable from control females. Shorter periods of oestrogen administration resulted in the production of hermaphrodites in which, characteristically, the testicular components developed more rapidly than ovarian elements. During the period of steroid administration, the fish were more susceptible to adverse conditions and there was some depression of growth. Following the cessation of treatment, the growth rate increased and size differences between treated and control populations, after 150 days, were not significant. Experiments with radioactively labelled oestradiol showed that the steroid enriched diet had an acceptable shelf life and that the half life of oestradiol in rainbow trout was less than 12 h. An alternative method of producing all-female stocks of salmonid fish by mating homogametic individuals in contingent, assuming the males to be heterogametic, on the development of a process for sex reversing the females. Oral administration of 17α methyltestosterone, at a concentration of 3 mg/kg diet, to rainbow trout and salmon for the period 0–90 days after first feeding, induced sex inversion of genetic females and resulted in substantially all-male populations. Treatment of salmon at a dose rate of 30 mg/kg diet resulted in stocks whose gonads had the characteristic filiform appearance of males but in which spermatogonial development had been suppressed. The usefulness of all-female stocks in commercial salmonid rearing operations is discussed.