On the mechanism of sperm release in three gobiid fishes (Teleostei: Gobiidae)

Embryonic and larval development of <i>Lipophrys pholis</i> (Pisces: Blenniidae)

“…Qasim (1956) reported that in the ovary, the position of the eggs is such that they must be extruded with the adhesion disc facing the substratum. This means that it is very likely that contact with sperm must precede attachment, either through the presence of sperm in the water column or by a sperm layer previously attached to the rocks by the male, as described for some gobiids (Marconato et al, 1996;Ota et al, 1996;Faria et al, 1998). Our observations suggest that the male probably applies sperm to the rock surface before egg attachment.…”

Individual adjustment of sperm expenditure accords with sperm competition theory

“…Moreover, the number of sneaker competitors can change within a single event, because the territorial male often chases away sneakers or other sneakers can join the spawning and nearly one third of spawnings occur without the presence of sneakers (23,24), which suggests that sneakers have the option not to compete with other sneakers and that sperm competition level can vary not only between but also within spawnings. Although grass and black goby sneakers have large testes (22), a careful allocation of their sperm stores may therefore be advantageous and may have selected for their ability to tailor their sperm expenditure according to the number of competitor males. Although this was beyond the scope of this study, our results suggest that sneakers can assess the level of sperm competition visually, because olfactory cues (territorial male's urine and female ovarian fluid) were kept constant and chemical communication between sneakers was prevented.…”

“…They were acclimated for 2 days in large outdoor tanks (120 liters) at the Chioggia Hydrobiological Station of the University of Padova, and released back into the wild after being used in the tests. Territorial and sneaker males were separated on the basis of body size, presence of sexual secondary characters, and ejaculate characteristics (22)(23)(24). Sexual maturity of males used in the experiments was confirmed by the release of a droplet of seminal fluid after the application of a gentle pressure on the abdomen.…”

“…Here we overcome these problems by using two shallow water gobiid fishes, the grass goby and the black goby, in which large, territorial males defend a nest in which females lay their eggs (22). During spawning sneaker males, which are usually younger and smaller than territorial ones, attempt to release their sperm either in the nest or in close proximity to it (22). Sperm competition is intense in these two species, because about 70% of the spawns have sneakers and up to six sneakers have been observed during spawning (23,24).…”

Sperm and milt characteristics and male v. female gametic investment in the Caribbean reef fish, Thalassoma bifasciatum

“…(3) A third alternative explanation for differences in sperm concentration between IP and TP male milt may be that the different mating modes require different milt characteristics (e.g. viscosity, Ruchon et al, 1995;Marconato et al, 1996) which may cause milt to dissolve and disperse at different rates. The body of water into which gametes are released is likely to have different properties between group-and pair-spawns simply due to the different amount of turbulent mixing caused by different numbers of fish turning around at the apex of the spawning rush.…”