In most salmonid species, sperm cryopreservation induces a drastic decrease in percentage of motile spermatozoa after thawing, and this is at odds with the high motility observed on cryopreserved sperm of most marine species studied. This study was carried out to investigate whether water salinity could modify sperm fitness to cryopreservation. During the 9 months preceding sexual maturation, 30 brown trout Salmo trutta f. fario males were reared in seawater, while 30 other males from the same family were reared in freshwater. Sperm was collected once and analyzed. Sperm motility was lower and more variable in the seawater group (10% to 90%; mean 55% +/- 29S.D.) than in the freshwater one (60% to 95%; mean 89% +/- 7S.D.). Resistance of spermatozoa plasma membrane to osmotic shock was assessed by calculating the time before 50% spermatozoa became permeable to propidium iodide upon exposure to deionized water. Fifty percent permeable cells occurred 2 min earlier in sperm from seawater fish than in sperm from freshwater fish. The two groups displayed the same sperm fatty-acid profile and the same sperm cholesterol/phospholipid ratio (0.526 +/-0.092S.D. in seawater fish vs. 0.523 +/-0.076S.D. in freshwater fish). Cryopreservation induced the same decrease in sperm ATP content in the two groups and fertilization rates were not different, whether fish were reared in seawater or in freshwater (27%+/- 12 and 32%+/- 12, respectively). It is concluded that water salinity is not a determinant of sperm fitness to cryopreservation, and that salinity is not a direct modulator of the cholesterol/phospholipid ratio.