Penpun SRISAKULTIEW
Thirty five Nile Tilapia (Oreochromis niloticus L. 1758) eggs or fry at the ages of 2 and 14 days post fertilization (dpf) were randomly selected and put into a 1L plastic bottle incubator. These were then immersed either in 0, 250 or 500μg/L of 17α-methyltestosterone (MT) for 6, 12, 24, 48, 72 and 96h separately. Controls were established using eggs or fry at the same age groups immersed only in ethanol (250μL/L) instead of MT at the same amount and duration. At the end of the treatment, they were washed and nursed in 10L plastic containers and 100L glass aquaria which were replenished with water according to their growth. They were fed with 40% protein pellet until 62 - 65dpf then dissected for gonadal sex determination using aceto-carmine squash method. The results showed that both the 250 and 500μg/L MT induced (P
