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

Abstract

Sperm motility variables from the milt 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 18–24h 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 KC1. 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 × 109 to 2–38 × lO10ml– 1 milt), declined in June and July (to 1–83 × lO10ml– 1 milt), and was followed by a steep increase in August (2–74 × 1010 ml– 1 milt). Mean seminal plasma osmolality remained relatively constant (250–265 mOsmol kg – 1) throughout the sampling period.