Characteristics and freezing tolerance of brown trout spermatozoa according to rearing water salinity

In most salmonid species, sperm cryopreservation induces a drastic decrease in percentage of motile spermatozoa after thawing, and this is at odds wit h the high motility observed on cryopreserved sperm of most marine species studied. This study was carried out to investigate whether water salinity c ould modify sperm fitness to cryopreservation. During the 9 months precedin g 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 fres hwater. 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 sper matozoa plasma membrane to osmotic shock was assessed by calculating the ti me before 50% spermatozoa became permeable to propidium iodide upon exposur e to deionized water. Fifty percent permeable cells occurred 2 min earlier in sperm from seawater fish than in sperm from freshwater fish. The two gro ups displayed the same sperm fatty-acid profile and the same sperm choleste rol/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 differ ent, whether fish were reared in seawater or in freshwater (27%+/- 12 and 3 2%+/- 12, respectively). It is concluded that water salinity is not a deter minant of sperm fitness to cryopreservation, and that salinity is not a dir ect modulator of the cholesterol/phospholipid ratio. (C) 2001 Elsevier Scie nce B.V. All rights reserved.