TURBIDITY AS A METHOD OF PREPARING SPERM DILUTIONS IN THE ECHINOID SPERM-EGG BIOASSAY

The use of a turbidimeter for preparing sperm dilutions used in the ec hinoid sperm/egg bioassay was evaluated. Regression analyses of the re lationship between sperm density and turbidity for the sea urchins Str ongylocentrolus purpuratus and Strongylocentrotus droebachiensis and t he sand dollar Dendraster excentricus indicated that although there we re slope differences for each species, each coefficient of determinati on was highly significant (p less-than-or-equal-to 0.001). For Dendras ter excentricus, triplicate hemacytometer counts over a range of turbi dities as well as repeated preparations of a single sperm turbidity in dicated similar variability for each. The use of the turbidimeter has time-saving advantages over conventional hemacytometer methods without sacrificing precision. Sperm dilutions can be prepared rapidly (1-2 m in), minimizing seawater sperm preactivation before test initiation, a nd may therefore contribute to increased test precision.