Monthly variation in sperm motility in common carp assessed using computer-assisted sperm analysis (CASA)

Sperm motility variables from the mill of the common carp Cyprinus carpio were assessed using a computer-assisted sperm analysis (CASA) system across several months (March-August 1992) known to encompass the natural spawning period. Two-year-old pond-raised males obtained each month were primed with an exogeneous hormone injection of carp pituitary extract and stripped of milt 18-24 h later. The milt was diluted, activated and videotaped using a high-speed (200 Hz) videocamera and recorder. Videotaped samples were subsequently analysed using the CellTrak/S CASA system (Motion Analysis Corp.) for percent motility, curvilinear and straight-line velocity. In addition to assessing changes in motility parameters across several months, a comparison was made between two predilution/activation media combinations (homologous seminal plasma/NaCl+HEPES v. 2-h incubation in 200 mM KCl+Tris/Tris). The percentage of motile cells assessed immediately after activation was significantly greater in the summer months (May, June, July) when compared to a spring sampling point (March); when assessed 1 min after activation, cells prediluted in seminal plasma maintained a higher percentage of motility than those prediluted in KCl. Curvilinear and straight-line velocities exhibited a slight seasonal trend; variations in response to the predilution treatments were observed with these measurements. Sperm count gradually increased through April and May (9.63 x 10.9 to 2.38 x 10(10) ml(-1) milt), declined in June and July (to 1.83 x 10(10) ml(-1) milt), and was followed by a steep increase in August (2.74 x 10(10) ml(-1) milt). Mean seminal plasma osmolality remained relatively constant (250-265 mOsmol kg(-1)) throughout the sampling period. (C) 1996 The Fisheries Society of the British Isles