Abstract
A rapid upward spawning rush is a nearly universal phenomenon among reef fishes that spawn pelagic eggs. Although spawning rushes have long been considered to have evolved as a defense against egg predators and/or attacks on the spawning fishes by piscivores, these hypotheses have never been tested in the field. We analysed piscivore attacks during three motor patterns associated with group spawning of the labrid fish Thalassoma cupido at Miyake-jima, I zu Islands, Japan. Egg predation on group spawnings was also quantified . Of 206 piscivore attacks on spawning fishes by seven predator species, 171 (83.1%) occurred during 461 spawning rushes (1/2.7 spawning rushes). No attacks were successful during spawning rushes, and only four kills were made in 206 attacks summed from all three motor patterns associated with spawning, amounting to a piscivore success rate of only 1.9%. In contrast, gametes from 90 of 213 spawnings (42.3%) were consumed by nine species of planktivorous fishes. Spawning fish seemed not to recognize egg predators and made no attempt to avoid them, often spawning in the midst of waiting aggregations of damselfishes. Our data indicate that the rapidly of the spawning rush of T. cupido serves as an excellent defense against piscivores, but is ineffective against egg predators. Evidence is presented from observations of seven other species suggesting that spawning ascents provide little protection against water column egg predators in predator-rich environments .
