SPERM MOTILITY IN TURBOT, SCOPHTHALMUS-MAXIMUS - INITIATION OF MOVEMENT AND CHANGES WITH TIME OF SWIMMING CHARACTERISTICS

Turbot sperm motility is observed using dark field microscopy and stro boscopic illumination combined with video recording. Sperm motility is triggered by dilution of spermatozoa in sea water or in non ionic med ia (glucose or saccharose), presenting osmotic pressure ranging from 3 00 to 2100 mOsmol. The percentage of motile spermatozoa reaches 100% u nder conditions of osmotic pressure of 300 to 1100 mOsmol and pH close to 8.0. In full sea water, glucose or saccharose solutions an aggluti nation of spermatozoa is observed; this is prevented by addition of bo vine serum albumin (5 mg ml(-1)). Immediately after transfer in activa tion solutions, 100% spermatozoa are motile in most samples freshly st ripped. This percentage drops suddenly between 15 and 30% after 70 to 100 sec. The beat frequency remains at a constant value of 50 Hz durin g 40 s post activation and then drops suddenly between 15 and 30 Hz. T he spermatozoa velocity is about 200 micrometers s(-1) during 30 to 40 s and then declines to a stable value of 100 micrometers s(-1) at 50 s post activation. After 1.20 mn, more and more spermatozoa become mot ionless. The minimum calculated and averaged distance covered during 1 .20 min, is about 12 mm. The high performances of turbot spermatozoa m otility are interpreted as a compensatory mechanism for the low sperm production.