Cryopreservation of sea bass (Dicentrarchus labrax) spermatozoa in experimental and production simulating conditions

A sperm cryopreservation protocol adapted from turbot, was tested on sea ba ss using either 250-mu L straws or 1.5-mL cryovials. A dilution to 1/3 in M ounib's extender and a cooling rate of 65 degrees C.min(-1) allowed frozen sperm to recover an initial motility similar to that of fresh sperm at thaw ing; however, significant differences in motility (P < 0.001, n = 10 fish s emen) were observed at further post-activation times, the motility decrease being faster in thawed sperm. At the experimental scale, triplicate insemi nations of 2-mL aliquots (approximately 2 000 eggs) showed a significant fe rtility decay of thawed sperm compared to that of fresh sperm (P < 0.01, n = 12 fish semen) when a discriminating 35.10(3) spermatozoa to egg ratio wa s applied. When 70.10(3) and 200.10(3) spermatozoa per egg were provided in the same experimental conditions, no significant difference appeared betwe en the fertilisation rates of fresh arid thawed sperm. In order to validate the procedure for production or cryobank purpose, a scaled-up protocol was established. Two and 50 mL batches of eggs (approximately 2.10(3) and 50.1 0(3) eggs, respectively) were inseminated in triplicate using either fresh or-thawed individual sperms of 5 males with 200.10(3) spermatozoa per egg. The mean fertility decreased by 23.5% due to cryopreservation. This decline was explained by the loss of fertility of only one sperm, and only in larg e-volume conditions, probably due to the delay of use after thawing. (C) If remer/Elsevier, Paris.