Environmental factors affecting the spawning burrow selection by the gobiid Valenciennea longipinnis

Spawning burrow selection by the longfinned goby Valenciennea longipinnis was studied in the near-shore moat on coral reefs, Okinawa, Japan. The gobies make several burrows within their home range, and spawn in one of them. To examine the factors important for spawning burrow selection three characteristics were investigated: current strength, burrow length and effect of underground water on the burrow. Among the burrows, pairs tended to spawn in a larger burrow irrespective of their body sizes. Most of the other non-spawning burrows were too small for a pair to stay together, because hard substrata may prevent the fish from excavating and shaping the burrow as they like. Moreover, pairs preferred to spawn in burrows where the underground water was oozing out, probably because the male's parental burden will decrease due to the higher dissolved oxygen concentration in such burrows. Although current strength may affect a water-exchange in a V. longipinnis burrow in relation to water-exchange function of a mound, it did not affect the spawning burrow selection because of the smaller velocity difference among the burrows relative to the daily fluctuation of tidal current.