Masculinization of Tilapia through Immersion in 17 α - Methyltestosterone or 17 α - Methyldihydrotestosterone

All-male populations are used in tilapia aquaculture because the culture of mixed-sex populations often results in precocious maturation and early reproduction (Mires, 1995). Early maturation shunts energy to gonadal rather than somatic growth. In addition, reproduction in ponds may lead to the harvest of many unmarketable fry. Individuals in mono-sex populations have increased somatic growth rate due to the avoidance of energy losses associated with gonadal development and reproduction. Furthermore, all-male tilapia populations are desirable because males achieve a larger final size than females (MacIntosh and Little, 1995). One of the most common techniques for producing mono-sex populations is steroid-induced sex inversion (Hunter and Donalsdon, 1983). This involves administering synthetic androgens or estrogens to differentiating fry. The steroids act as sex-inversion agents by functionally masculinizing or feminizing individuals in the population. Several methods of steroid administration are possible, including injection, feeding of steroid, and immersion of fry in steroid solutions. Due to their non-invasive nature, the latter two are the most practical for application to aquaculture.