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Objective: Study of histological changes in gonads of fish
received a variety treatment of 1 7-a methyl testosterone.
Animals: Rainbow trout ( Oncorhynchus mykiss).
Design: Descriptive study.
Methods: Application of 17-a methyl testosterone (MT)
using immersion and/or oral administration methods in two
seasons and in 5 and 11 treatments along with a control
group with no hormonal treatment for each season,
respectively. In immersion method eyed eggs and larvae
were immersed in 250 mg/l MT bath for 2 hours twice 4
and 8 days apart. In oral administration method newly
feeding larvae were fed with food containing 0.5, 1, 2, 3
and 30 ppm MT for 60, 70, 90 and 120 days after
commencing active feeding. Histological examination was
carried out on gonads of 20 fish from each treatment as
well as control group at the age of 11 and 24 months for two seasonal groups of fish, respectively.
Results: Masculinization and sterilization were
successfully carried out on rainbow trout by using a variety
treatment of MT. A range of histological changes were
observed in gonads of different treatment groups. This
included histologically normal males, normal females,
intersex, totally atrophic gonads and sterile fish. [n some
testes a number of follicles were seen among the mass of
spermatozoa. In intersex gonads both male and female cell
types were observed alongside each other. Sterile gonads
could be categorized as: sterile males, sterile females as
well as completely sterile containing residual male cells,
residual female cells and no cells at all, respectively. In a
number of specimens spermatozoon cysts were typically
observed.
Conclusion: Application of 17-a methyl testosterone to
rainbow trout at early stages of development could
dramatically change the histological profile of gonads
ranging from functional testes, to interrex, to sterility.
J.Fac.Vet.Med. Univ. Tehran. 61,2:187-193,2006