Sperm morphology and its influence on swimming speed in Atlantic cod

A protocol for staining fish spermatozoa using Hemacolor-stain was developed for light microscopy and successfully applied to Atlantic cod ( Gadus morhua ). Sperm head morphology was characterized by size (length, width, area and perimeter) and shape (ellipticity, rugosity, elongation and regularity) (n   =   6500 spermatozoa), and tail length (n   =   260 spermatozoa) of 12 individual cod. Two spermatozoa heads sperm were clearly identified: round and elongated, being this last one more abundant (86.3%). No evidence was detected in tail length for both head types. Tails were 96.4% length of sperm and no difference in tail length was detected between head types. A positive correlation existed between head and tail length, with variability existing among males. Sperm swimming speeds varied among males with a maximum curvilinear velocity between 151.5 and 201.5  μ m s⁻¹. Mean swimming speed declined by 8.2% from 30 to 70 s post-activation. Spermatocrit was negatively correlated with curvilinear velocity at 30 s post-activation. Males with short sperm heads maintained their swimming velocity for longer periods that those with long heads. Fulton's condition factor was negatively correlated with straightness of path.