Sex reversal in black crappie Pomoxis nigromaculatus:: effect of oral administration of 17α-methyltestosterone on two age classes

The masculinizing effect of 17 alpha-methyltestosterone (MT) on two age classes of black crappie Pomoxis nigromaculatus was investigated. Broodstock were induced to spawn by intramuscular injection of human chorionic gonadotropin hormone (hCG). Fry produced were divided into two age classes, age I (40 days old), and age II (60 days old). Age I fry were fed to satiety with feed containing MT at a concentration of 0, 30, or 60 mg/kg feed. Age II fry were fed MT at 60 mg/kg feed only. Both age classes were fed hormone treated diet for 30 days. Mean initial weight and length of age I fry were 0.21 +/- 0.15 g and 23 +/- 2.2 mm, respectively (mean +/- SD), whereas age II fry were 0.22 +/- 0.10 g and 24 +/- 3.4 mm, respectively. Age I fry fed with 60 mg MT/kg feed yielded the highest (90%) mean percent males relative to all treatments (P < 0.01). Age I fry fed with 30 mg MT/kg feed produced 71% mean percent males that was significantly higher (P < 0.05) than age II fry fed with 60 mg MT/kg feed, and fry fed with control diet (P < 0.01). There was no significant difference in percent males between age II fry (58%) and control (51%). Two patterns of ovotestis were identified by histological examination. One pattern was dominated by ovarian tissue or Ovotestis-Mainly Testicular (OTMO), the other was dominated by testicular tissue or Ovotestis-Mainly Testicular (OTMT). Sex reversal in black crappie seems to be influenced by age more than size. This study reports the first successful masculinization of this species by hormonal treatment. (C) 1997 Published by Elsevier Science B.V.