The effect of osmolality on egg fertilization in common carp, Cyprinus carpio Linnaeus, 1758

Abstract

The aim of the study was to investigate the effect of osmolality of the activating solution (AS) on in vitro fertilization of the eggs of common carp, Cyprinus carpio L. Four different AS (NaCl solutions) were used with different osmolalities: AS-0 (distilled water), AS-100 (100 mOsm kg−1), AS-200 (200 mOsm kg−1) and AS-300 (300 mOsm kg−1). Fertilization was performed in Petri dishes using freshly collected sperm. Insemination (sperm addition to activated eggs) was preceded by exposure of egg samples to each AS for 0 (control group), 15, 30, 60, 90, 120, 150, 180, 210, 240, 270, 300, 330 and 360 s. Embryonic survival was determined 24 h after incubation at 20°C. Additionally, motility parameters (motility rate [MOT, %] and curvilinear velocity [VCL, μm s−1]) of the spermatozoa activated with the tested AS were measured using a CASA (computer-assisted sperm analysis) system. Motility duration (DUR, s) in each AS was also determined. The results revealed a significant effect of osmolality of the AS on the fertilizing capacity of common carp eggs. There were no viable embryos in the group AS-300. In the group AS-0, the eggs lost their ability for fertilization after 90 s; in the remaining groups, eggs could be fertilized for up to 150 s (group AS-100) or 360 s (group AS-200). Fertilization failure in the group AS-300 was caused by the lack of spermatozoa activation in this solution. The present study findings for in vitro common carp fertilization indicate that special attention should be given to the AS osmolality, where 100 mOsm kg−1 was found to be the most suitable.