MEPS 161:61-70 (1997)  -  doi:10.3354/meps161061

Accurate measurement of fertilization rate (FR) is essential for reproductive studies of pelagically spawning marine organisms. We compared the reliability of 3 methods of collecting eggs for estimates of FR in the coral reef fish Thalassoma bifasciatum: collecting in hand-held nets 30 s after spawning or in plastic bags 3 to 4 s ('early bag') or 30 s ('late bag') after spawning. FRs were significantly and consistently lower in eggs collected by net than in eggs collected in early or late bags. FRs were consistently highest in late bags. In field experiments, netted samples contained higher proportions of negatively buoyant, unfertilized eggs and the negative effects of the net declined with increasing time from initial exposure of eggs to seawater and sperm. Thus, the net appeared to interfere mechanically with the fertilization process. FRs were not higher in smaller than in larger bags, as would have been expected if bags artificially prolonged high average sperm concentration around eggs. The average concentration of sperm in a bag containing twice the largest number of sperm ever collected in any spawn was less than the minimum sperm concentration needed to initiate fertilization. Thus, the difference in FR between netted and bagged samples was not the result of prolonged maintenance of an artificially high average sperm concentration in the bag. Using bag collection techniques, we compared FRs for pair and group spawns. Mean FRs ranged from 86.6 to 99.5%, with analyzable variance. Contrary to the results of a previous study using netted samples, group spawns had significantly higher FRs than pair spawns using early bag samples. Female mating tactics ought to be influenced evolutionarily by this difference between pair and group spawns.

Fertilization rates · Methods · Pair spawns · Group spawns · Reef fish