The effects of sperm density and gamete contact time on the fertilisation success of blacklip (Haliotis rubra; Leach, 1814) and greenlip (H. laevigata; Donovan, 1808) abalone

A factorial experiment, in which blacklip (Haliotis rubra; Leach, 1814) and greenlip abalone eggs (H. laevigata; Donovan, 1808) were exposed to a range of conspecific sperm densities (ca. 104-107 sperm mL -1) for different time intervals (7-2,400 s), showed there was a significant interaction between these factors in both species. Prolonged exposure (i.e., 1,200-2,400 s for blacklips and 480-2,400 s for greenlips) to concentrated sperm (i.e., 107 sperm mL-1) resulted in lysis of the egg membrane and polyspermy. Analysis of CoVariance of F 50 values (i.e., the sperm concentration required for 50% fertilization, derived from the linear regression of logit (proportion of eggs fertilized) versus sperm density) between species across a range of contact times demonstrated that contact time had a significant effect (P < 0.001) whereas species did not (P = 0.22). The lack of a species effect suggests that the fertilization potential of blacklip and greenlip abalone eggs are similar, at least across the range of sperm densities and contact times used. An examination of sperm morphology using scanning electron microscopy of both species revealed similarities in sperm length (i.e., 42-46 μm) and differences in the shape of acrosome, the tip of which was blunt in blacklip sperm and V-shaped in greenlip sperm. Morphological differences in haliotid sperm are discussed in relation to species differences in fertilization kinetics.