Forcipiger longirostris is one of the 3 members of the genus Forcipiger, which together with 11 additional genera make up the butterflyfishes family (Chaetodontidae) in which a total of 129 species are currently described. It is the species with the widest distribution, covering territories of both the Indian Ocean and the Pacific Ocean. It is present from the waters of Mozambique to the archipelago of Hawaii and the Pitcairn Islands. It is associated with coral environments up to 200 meters deep, although the first 50 meters is where it is most frequent.
The body of Forcipiger longirostris is tall, laterally compressed, relatively oval and has a very elongated rostrum, with a tubular snout ending in a very small mouth. They can grow up to 19 cm in total length. The dorsal fin has 10-11 spines with strongly indented interspinal membranes, and 19-25 soft rays. The anal fin has 3 spines and 17-19 soft rays. The ventral fins have only a single spine and 5 soft rays, while the caudal fin is more or less truncated.
As for the coloration of Forcipiger longirostris, the dominant color of the body is bright yellow. Only the head region is a different color. The upper half of the head, horizontally across the eyes, is blackish, while the lower triangle of the rostrum is white. The dorsal, anal and ventral fins are completely yellow, while the pectoral and caudal fins are translucent. The dorsal and anal fins are notable because the outermost regions of the soft rays are electric blue. It is also striking a black spot located at the rear end of the anal fin, next to the caudal peduncle, which is an ocellar spot in order to mislead potential predators.
It is very common and easy to confuse the specimens of Forcipiger longirostris with the evolutionarily close and much more frequent Forcipiger flavissimus. The differences between these two species can go unnoticed, although there are some features that make their differentiation possible. In the case of Forcipiger flavissimus the snout is not as long as that of Forcipiger longirostris (up to 1.5 times longer in this species), and the mouth in Forcipiger longirostris is much smaller than that of its close relative. Another difference from Forcipiger longirostris is the presence of black mottling on the throat and chest region, so its absence would be indicative of Forcipiger flavissimus specimens. The third trait may go completely unnoticed, since Forcipiger longirostris has between 1 and 2 fewer spines on the dorsal fin.
The diet, as can be deduced from its more than specialized snout, is based on very small animals that can be found among the corals and rocks, such as some crustaceans, hydrozoans, copepods and certain algae.
Forcipiger longirostris is usually a solitary species but it is also possible to find it in small groups. During the reproductive season they form pairs that will release eggs and sperm into the water column, so that fertilization occurs and the dominant currents spread their small eggs over a vast territory.Photos: