Forty m/ale channel catfish (Ictalurus punctatus) of two age groups and two stocks (domestic and wild) were compared in an experiment to study morphological and physiological characteristics of their testes and sperm cells from May through October. The gonosomatic index for 36 normal catfish examined averaged 0.25%. An average of 82.7% spermatozoa were alive with an average motility score of 2.96. These fish had an average gonadal sperm concentration of 7.1 X 109spermatozoa per g wet testicular tissue. The testes were found to be composed of 2/3 spermatogenic and 1/3 glandular tissue. There were no morphological changes observed in the characteristics of the spermatogenic tissue during the period of study. The 3-year-old fish were consistently larger than the 2-year-olds, and the domestic fish were larger than the wild stock in each age group, which probably caused most of the differences in characteristics when comparisons were made.