Effects of synthetic and natural steroids on the growth, sex reversal and gonadal development of rainbow trout, Oncorhynchus mykiss (Walbaum) Doğal ve sentetik steroidlerin Gökkuşağı alabalığında, Oncorhynchus mykiss (Walbaum) gonadal gelişim, cinsiyet dönüşümü ve büyüme üzerine etkileri

Indirect methods such as masculinizing treatments by synthetic sex steroids has widely been used to produce all-female stocks in salmonids, but they have some disadvantage such as toxicity and high cost. Therefore, the main objective of this research was to develop indirect methods for the production of allfemale populations of Oncorhynchus mykiss through the use of natural steroids.In this study seven thousand prelarval rainbow trout were divided evenly among seven tanks and fed a commercial starter trout diet supplemented with synthetic (3, 6 mg testosterone and methyltestosterone kg-1 diet) and natural steroids (50 and 100 mg Tribulus terrestris kg-1 diet) during 90 days after hatching. Fish were then further reared on a commercial trout diet until sex ratios could be determined through histological and macroscopic observations. The Tribulus terrestris (50 and100 mg/ kg) treatments yielded 55–63% males, while the testosterone (3 and 6 mg/ kg) treatment yielded 51–53% male population. This demonstrates that Tribulus terrestris was effective in the direct masculinization of rainbow trout compared to testosterone, but no significant difference was observed between groups. Also, this study was the first attempt that yielding higher growth of Oncorhynchus mykiss fed with diets containing TT (100 mg kg-1 diet) compared to other experimental groups. There were no marked differences in the structure of the undifferentiated gonads between the control group and all treatment groups. In conclusion, the effects of higher concentrations (150, 200, 250 mg kg-1) of TT should be investigated to reach the higher sex reversal and growth rates, and also determined the blood testosterone levels, gonadal structure of rainbow trout and/or other salmonids, and cultivable fish species.