Successful Sex Reversal of Brook Trout with 17α‐Methyldihydrotestosterone Treatments

Abstract

Monosex female stocks are widely used in the commercial production of rainbow trout Oncorhynchus mykiss. The potential for commercial production of brook trout Salvelinus fontinalis, however, is constrained by the lack of published protocols for producing the sex‐reversed males required to create monosex female stocks. Immersion and immersion plus feeding treatments with 17α‐methyltestosterone (MT) and 17α‐methyldihydrotestosterone (MDHT) were applied to genotypically female gynogenetic brook trout to induce phenotypic sex reversal. The fry were exposed to a 6‐h immersion in a solution of MT or MDHT on day 10 following completion of hatch and/or to a steroid‐treated diet for 60 d beginning at first feeding. Immersion dosages were 0.5 or 1.0 mg/L, and feeding dosages were 1.0 or 2.0 mg/kg of feed for MT and 0.5 or 1.0 mg/kg for MDHT. Phenotypic sex of the fish was determined 19 or 22 months after first feeding. Control gynogenetic fish were 100% phenotypic females. Treatments with MT had minimal effect: most fish remained female, with only a low incidence of phenotypic males (1–3% in four of the treatments), intersex fish, or sterile fish. In contrast, a substantial number of phenotypic males were observed in several of the MDHT treatments, with the highest proportion (45%) occurring in the 0.5 mg/L immersion plus 0.5 mg/kg feeding treatment. Sperm was obtained from 29 males from five MDHT treatment groups and one MT treatment group examined at maturity (22 months) and was used in progeny tests of these males. The progeny were 100% female, confirming the male parents to be genotypically female. These protocols may be used to create sex‐reversed brook trout males for the production of monosex female progeny, although additional trials are ongoing to test similar MDHT immersion dosages applied once or multiple times, with or without feeding treatments, to identify protocols with increased efficacy.

Gonadal differentiation and hormonal sex reversal in arctic charr (Salvelinus alpinus)

“…Piferrer and Donaldson ('92) described similar ''affected'' gonads in chinook salmon which may have been due to steroid administration outside of the labile period. This is supported by the fact that the optimum concentration of MDHT for sex reversal by immersion in this study was 10-20 times higher than is typical for other salmonids, whereas the optimal concentration for sex reversal by feeding was not (Herman and Kincaid, '91;Galbreath et al, 2003).…”

“…One of the primary constraints to commercially viable culture of Arctic charr is early sexual maturation, especially among males (Galbreath et al, 2003). Sexual maturity affects flesh quality of farmed fish, as protein and lipid energy stores are transferred from the muscle to the developing gonads.…”

“…Previous studies on sex control in salmonids, such as brook charr, rainbow trout, Atlantic salmon and Pacific salmon (Oncorhynchus spp.) (Herman and Kincaid, '91;Chevassus and Kreig, '92;Feist et al, '95;Galbreath et al, 2003), suggest that there are differences among species in relation to the steroid concentration and treatment duration needed for sex reversal. Species-specific characteristics may include the number of steroid receptors, steroid metabolism and the degree of gonadal development at the time of treatment (Piferrer, 2001).…”

Controlling preharvest maturity in farmed Arctic char: A review from the Canadian perspective

“…Given that all salmonid fishes have female-homogametic sex determination (equivalent to the mammalian XX-female/XY-male system), crossing a neomale with a normal female results in all-female offspring (Baroiller & D'Cotta, 2016;Piferrer, 2001). This approach to producing all-female populations is used extensively in the rainbow trout industry (Krisfalusi & Cloud, 1999) and has also been demonstrated to be effective in other salmonid and nonsalmonid species, such as Atlantic salmon, Salmo salar L. (Lee, King, & Pankhurst, 2003), Arctic charr, S. alpinus Linnaeus (M. Chiasson & Benfey, 2007), brook char, Salvelinus fontinalis Mitchill (Galbreath, Adams, & Sherrill, 2003), and Atlantic halibut, Hippoglossus hippoglossus L. (Lin, Benfey, & Martin-Robichaud, 2012). The key steps for optimizing the production of all-female populations are (a) determining the developmental stage at which gonadal differentiation occurs and is therefore malleable, (b) optimizing dosage and duration of treatment with masculinizing agents, and (c) distinguishing neomales from normal males for breeding purposes.…”

“…While protocols for the production of all-female populations have been extensively studied in related salmon and trout species (Oncorhynchus and Salmo spp.) (Fatima et al, 2016;Galbreath et al, 2003;Krisfalusi & Cloud, 1999;Lee et al, 2003), little information is available for Salvelinus spp. (M. Chiasson & Benfey, 2007;Gillet, Vauchez, & Haffray, 2001).…”