Effects of 17α-methyltestosterone on blood parameters, visceral morphology, and sex reversal in rainbow trout

Aim: To evaluate the effects of 17α-methyltestosterone treatments on growth performance, morphological and biochemical blood parameters, condition of internal organs, and sex reversal in juvenile rainbow trout.

Methods: Experiments were conducted on larvae and juveniles that received feed supplemented with 17α-methyltestosterone for 3, 4, and 8 weeks after the onset of exogenous feeding. The influence of the hormone was assessed based on hematological and biochemical blood indicators, as well as histological examinations of internal organs.

Novelty: A comprehensive assessment of the long-term consequences of hormonal sex reversal in rainbow trout was performed 15 months after 17α-methyltestosterone application. The study revealed that treatment duration significantly affected hematological and biochemical blood parameters, while no adverse effect on internal organs was detected, except for the reproductive system.

Results: The inclusion of the hormone in feed for 4 weeks resulted in up to 90 % males. Extending the treatment to 8 weeks led to the formation of up to 90 % sterile individuals. Long-term effects were manifested as a minor nonlinear decrease in hemoglobin, hematocrit, and erythrocyte counts, accompanied by an increase in leukocyte and platelet proportions. Significant reductions in albumin, total protein, and creatinine concentrations were recorded, along with slight decreases in AST activity, blood urea nitrogen, and triglycerides. However, all variations remained within reference ranges. Histological examination of the liver, intestine, heart, and spleen of trout aged 5 and 15 months demonstrated normal ontogenetic changes without pronounced structural alterations attributable to the treatment.

Practical significance: The study confirmed that early-life administration of 17α-methyltestosterone does not negatively affect the functional state of juvenile organs and is an effective approach for producing up to 90 % males when applied for a 4-week feeding period.

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