Objective: To optimize the dose and rout of administration of 170,¬methyltestosterone for masculinization and sterilization of rainbow
trout.
Animals: Rainbow trout, Oncorhynchus mykiss.
Procedure: Oral administration of 17o'-methyltestosterone in I 1
treatments as follows: in AI, A2, A6 and A 7 treatments 0.5, 1,2 and 3 ppm, respectively, all starting from active feeding of larvae for 60 days; in A3 and A8 treatments 1 and 3 ppm, respectively, both starting from active feeding of larvae for 90 days; in A4 and A9 treatments 1 and 3 ppm, respectively, starting two weeks after active feeding of larvae for 60 days; in A5 and Al 0 treatments 1 and 3 ppm, respectively, starting four weeks after active feeding of larvae for 60 days; and in A 11 treatment 30 ppm starting from active feeding of larvae for 120 days as well as control group with no hormonal treatment. Twenty fish from each treatment and control
groups were examined histologically at the age of 11 months to determine
the sex ratio including female, male, intersex and sterile fish.
Statistical analysis: Sex ratios and growth rates were analyzed
using chi square andANOVA, respectively and the mean survival
rates were comparal by student "t" test.
Results: In sample taken from Al treatment 100% of fish were
males. Other samples showed a variety of results (percentage of males is shown in brackets): A2 (90%), A6 (95%), A3 (80%), A4
(80%), A9 (68%), A7 (65%), A8 (50%), A5 (45%), AI0 (45%). In
A 11 treatment no males were found. All treatments adopted for masculinization except for A5 and A1O changed the sex ratio highly
significantly (P
group significantly (P
in growth of fisch taken from the treatment groups compared to the
control group.
Conclusion: According to histological evidence and statistical
analysis of data as well as considering the minimum usage of
hormone it can be concluded that the oral administration of
0.5 ppm 17a-methyltestosterone starting from active feeding of
rainbow trout larvae for 60 days was determined as to be the
optimum treatment. J. Fac. Vet. Med. Univ. Tehran. 58, 3: 235¬
240, 2003.
)