Use of Sex Reversal in Striped Bass to Create an All‐Male Population

Dietary administration of 17 α‐methyltestosterone (MT) was used to reverse the sex of striped bass Morone saxatilis to create phenotypic males that were genetically female. Fish were exposed to steroid regimes at various times to determine the labile period for effective sex reversal. Methyltestosterone was administered either by dry feed (2.5, 5, 10, 20, and 40 mg/kg) from 19 to 60 d posthatch (dph) or by feeding nauplii of Artemia franciscana cultured in MT media (2.5, 5, and 10 mg/L) from 6 to 30 dph. Sampling at 1 year revealed that a treatment of 2.5 mg MT/kg of formula diet altered the sex ratios significantly from an expected ratio of 1:1 and produced 82% males (N = 28, P < 0.05). Controls and other treatment levels did not differ from a 1:1 sex ratio. Some ovaries had delayed gamete development that was characterized by the presence of significantly more stage‐I ova than stage‐III ova compared with those from control females of a similar size. A few fish were intersex or sterile. The brine shrimp treatment proved unsuccessful in altering sex ratios. This suggests that either the labile period of maximum gonadal hormone sensitivity in striped bass occurs between 30 and 60 dph and that the 2.5 mg MT/kg feed is the optimal dosage to induce sex reversal or that feeding brine shrimp is not an efficacious means of hormone delivery.