Endocrine technologies and sex modification of fish stocks are playing an increasingly important role in commercial aquaculture production. The characteristics and fertilization success of sperm from masculinized coho salmon (Oncorhvnchus kisutch) were examined and compared to that of regular coho salmon sperm. Sperm from masculinized XX males was stripped, or when the efferent ducts were not developed the semen was collected from the testis, and compared with semen from normal XY males. Stripped masculinized genetic females exhibited similar measures of sperm velocity and sperm density as normal male echo salmon, with both of these groups differing significantly from testicular sperm from masculinized females. In commercial fertilization trials, fertilization success was not altered by the dichotomy observed between testicular and stripped milt from masculinized females. Treatment with leutenizing hormone releasing analogues had no effect on sperm motility, density, or fertility. Much of the difference in sperm characteristics can be attributed to the difference between stripped sperm and testicular sperm. (c) 2005 Published by Elsevier B.V.