Beauty of the reef

Giovanna Fasanelli | VOLUME 28, ISSUE 5

If there were a beauty pageant for filefish, I am certain this creature would drive away with the latest BMW. The longnose filefish, also known as the orange spotted filefish, harlequin filefish or, here in Australia, as the beaked leatherjacket (oxymonacanthus longirostris) is a welcome sight on any tropical reef system in the Indo-Pacific.

With a largely inflexible diet consisting primarily of live staghorn and table coral polyps from the genus acropora, this species’s presence is usually indicative of a healthy coral reef system.

Large adults are commonly encountered in heterosexual pairs or in small family groups, all sharing the same feeding territory. The pair’s territory is rigorously defended by the male, especially as the breeding season heats up. By embracing the territorial pair bond system, the male is afforded exclusive access to a guaranteed female, while the female enjoys the testosterone-fuelled protection offered by the male, allowing her to feed to her heart’s content. A secure, well-fed, healthy female is also of benefit to the male as he is given extra assurance that his genetic line will be fighting fit.

But although this mating strategy appears to be the norm, a study in Japan revealed that toward the end of the breeding season, 20 per cent of males became polygynous, roaming through territories and mating with different females. Females whose partners were polygynous appeared to lay smaller eggs as a result of decreased feeding frequency. Once the deed is done (which, by the way, occurs daily) and the male has fertilised the female’s eggs, she lays them at the base of some dead coral or hidden within a clump of filamentous algae. Then, just after sunset on the second day after spawning, the eggs hatch and the larvae float away to join the plankton soup ready for the ultimate test: surviving to maturity.

Reaching a maximum length of around 9cm, these dazzling beauties have a distinctive way of swimming: while undulating their dorsal and anal fins in the same fashion as do their cousins, the triggerfish, they point their long mouths down into the coral colony, expertly plucking out the live polyps from their calcium carbonate cups. When threatened they will quickly sink into the maze of spiky staghorn branches revealing only a black spot on their protruding tails, which may trick predators into thinking their tails are, in fact, heads.

The males have a bright orange-red coloured ventral flap that they flash during courtship or territorial disputes. They will also flick their thick, orange dorsal spine forward and dip their heads to create the effect of a sword – a suitable tactic when deterring other marauding fishes from feasting on the newly laid eggs.

It’s for good reason their Latin name translates as ‘sharp one thorn long nose’. Any Indian chief would be jealous of that name!

CLASSIFICATION

Species: Longirostris

Genus: Oxymonacanthus

Family: Monacanthidae

Order: Tetraodontiformes

Class: Actinopterygii

Subphylum: Vertebrata

Phylum: Chordata

Kingdom: Animalia


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