Spermatocrit and spermatozoa density in Atlantic cod (Gadus morhua): correlation and variation during the spawning season

The utility of spermatocrit (the proportion of solid packed material in sem en after centrifugation) as an indicator of spermatozoa density and male sp awning stage was tested in Atlantic cod (Gadus morhua). Semen was collected from captive male cod over three spawning seasons. Spermatocrit was positi vely and significantly correlated with spermatozoa density measured with a Coulter counter (Multisizer), but not with spermatozoa counts in a haemacyt ometer. Spermatocrit increased significantly as the spawning season progres sed. However, day of season explained only 35% of the variation because spe rmatocrit varied among individual males. Spermatozoa size remained unchange d throughout the sampling period and was not correlated with spermatocrit, indicating that variation in spermatocrit was due to variation in spermatoz oa number and not their size. Spermatocrit is a good estimator of sperm den sity but is not reliable as indicator of spawning stage because of the vari ation among individual males. (C) 1999 Elsevier Science B.V. All rights res erved.