The production of hermaphrodites of Atlantic cod (Gadus morhua) by masculinization with orally administered 17-α-methyltestosterone, and subsequent production of all-female cod populations

In order to masculinize Atlantic cod (Gadus morhua) with the ultimate goal to produce all-female populations, larvae were treated with dietary 17 alpha-methyltestosteron (MT) at high (H: 15 mg/kg diet) and low (L: 5 mg/kg diet) dosages for varying time-periods from either 12 or 16 mm total length (TL) lasting up to 16 mm, 21 mm or 25 mm. The results determined by macroscopic and histological evaluation (n = 30 per group) showed that MT were successful in producing hermaphrodites at a dose / duration dependent response, with the highest incidence of hermaphrodites (46.7%) in the groups that were treated for the longest time period at the high dose (the 12-25H group). The treatment groups 12-25L, 12-21H and 12-21L also had high incidences of hermaphrodites, with 32.2%, 29% and 24.1%, respectively, while 0% was observed in the 12-16L and 16-21H groups. The remaining groups had only a few hermaphrodites. The control group had a sex ratio of 46.7% males and 53.3% females and no hermaphrodites. At two years of age, 3 hermaphrodites and 1 control male were selected on the basis of their plasma ratio of 11-ketotestosterone:estradiol-17 beta (11KT:E2). The sperm was used to fertilize the eggs of normal females with the aim to produce three all-female and one control population. The sex of the F1 generation was determined at 10 months of age (n = 50 pr group), revealing 100% females in the offspring of all three hermaphrodites, whereas the offspring of the control male consisted of 54.2% females and 45.8% males. These results provide evidence of female homogamety in Atlantic cod. (C) 2010 Elsevier B.V. All rights reserved.