Spawning, eggs and larvae of the longnose filefish Oxymonacanthus longirostris, a monogamous coralivore

Synopsis

The longnose filefish (Monacanthidae, Oxymonacanthus longirostris) was studied at a patch reef on Enewetak Atoll. It swims with undulations of its median fins and feeds almost continuously on coral polyps, using its beak-like mouth. The spot in the tail resembles an eye so that the tail looks like a head when it protrudes from the coral during feeding. There is slight dichromatism in that males have brighter pelvic flaps. Most of the fish were color tagged for individual recognition. They tended to remain within a given area, although some fish roamed throughout the patch. Most of the larger adults formed monogamous pairs; the smaller fish were variously alone or in groups of 1–5 individuals who appeared to know one another. Only pairs having the largest males, on the periphery of the patch, were clearly territorial. Aggression was a common event featuring a few distinctive displays, most of which were used in courtship as well. Spawning may be a daily event, occurring around 1600 h. The female probes and selects a tuft of blue-green algae; the male nuzzles the female and they spawn in the algae. The green eggs are about 0.7 mm in diameter, demersal, adhesive, and hidden in the algae; they hatched in 53.5 h, just after sunset. The planktonic larvae fit the monacanthid type B of Leis & Rennis (1983) and were initially 2.5 mm TL; by day 5 their yolk was gone.