The structural features of the gonads of rainbow trout (Oncorhynchus mykiss) after treatment for the production of monosex females and triploid fish are described. The treated groups were: 1) monosex production by hormonal treatment, 2) monosex production by gynogenesis and 3) triploidy condition, Criteria were stablished for the description of gonads for the treated groups. The results of this study improve the methodology commonly used to measure the sexual proportion of treated groups.01FONDEF002FONDEF28