Abstract: The objectives of this study were to assess the suitability of spermatocrit as arapid estimator of sperm density in Rainbow trout with 1 year old. At the end of the spawning season, semen was collected without anesthesia by abdominal massage from 11 Rainbow trout. Sperm concentrations were assessed for milt samples taken from males using a haemocytometer and spermatocrit. In these fish, spermatocrit and haemocytometer averaged 46.09 % and 2.5 x 109 /ml, respectively, for 33 milt samples collected from males. There were significant correlation between spermatocrit readings and sperm concentration. Regression analysis showed a significant positive linear relationship between body weight and total lenght. It was determined that sperm concentration measured by spermatocrit as as a rapid estimator of sperm concentration in Rainbow trout.