Characterization of rainbow trout milt collected with a catheter: semen parameters and cryopreservation success

Collection of fish milt by stripping risks the danger of milt contamination by urine. This may seriously influence milt characteristics and quality, i ncluding usefulness for cryopreservation. Urine contamination of milt may b e avoided by using a catheter for sperm collection. The objectives of this study were to provide basic characteristics of milt collected with a cathet er, to test the usefulness of this milt for cryopreservation, and to correl ate characteristics of fresh and cryopreserved semen with sperm fertility r ates. Milt from 25 rainbow trout Oncorhynchus mykiss (Walbaum) males were u sed. All samples were cryopreserved using the pellet method within 1 h of c ollection, using 0.6 M sucrose and 10% dimethyl sulphoxide (DMSO) as an ext ender. Catheterization resulted in semen of very good motility (> 90% motil e spermatozoa) and high fertilization rates after cryopreservation (mean fe rtilization rate 81.8 +/- 13.3% of control, at a sperm/egg ratio of 2.4 +/- 0.3 x 10(6)). Osmolality of seminal plasma and concentrations of sodium, p otassium and magnesium ions had low variability, which suggests that they a re important for creating a stable environment for sperm storage in the spe rm duct. Higher variability of certain seminal plasma characteristics, such as protein concentration and antiproteinase activity, suggests that these characteristics are related to individual semen features of particular male s. A strong correlation of seminal plasma zinc concentration with protein c oncentration may reflect an importance of zinc in semen biology. Cryopreser vation caused a significant release of protein and acid phosphatase from sp ermatozoa. Our results did not reveal any single characteristic of semen co llected by catheter that could be used as a powerful predictor of cryoprese rvation success, presumably because all samples were of high quality.