The Hawaiian filefish

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The Hawaiian filefish is both rarely seen and incredibly common, depending on when you are looking for it! We explain why...

If any fish is a true enigma, Pervagor spilosoma is that fish — a species that’s one of a handful that exhibit a poorly understood breeding strategy called episodic spawning.

Although said to be the most common filefish species in Hawaiian waters, it’s comparatively rare on reefs most of the time and not often seen in large numbers.

However, perhaps just a couple of times a decade, something very strange happens — and becomes part of Hawaiian folklore.

Vast numbers appear on Hawaii’s reefs and undergo a population explosion, going from being a relative rarity among the reef’s fish fauna to being the most abundant fish species around. They gather in the shallows of the islands and become so numerous inshore that they spill into deeper habitats.

Yet this phenomenon doesn’t happen often. It was particularly notable in 1944, 1975 and 1982-1987 when millions gathered, but, as yet, scientists don’t really know precisely why it occurs when it does.

Many are picked off by predators, such as frigate birds, or die – apparently naturally ­– and large numbers wash ashore, pile up on local beaches and rot in the sun.

Early Hawaiians are said to have believed that the appearance on the shores of all these dead fish prophesied the death of a great king or chief.

Studies on the species suggest it doesn’t spawn very often, but when it does it does so in spectacular style, perhaps timing spawning to coincide with something that means the fry have a much greater chances of survival.

It is apparently not linked to ocean circulation patterns, as the filefish are the only fish that do it. Unfortunately, numbers get so high that some just don’t survive long. These fish have an exceptionally long pelagic-juvenile stage and some experts reckon this might be a link.

What are filefishes?

Filefishes, or leatherjackets, are members of the monacanthid family and found mainly around the Indo-West Pacific region. They are closely related to triggerfishes, but fairly simple to tell apart. The chunky first spine on their dorsal fin is positioned above the eye, but much further back in triggers.

Factfile

Common name: Fan-tailed filefish. Hawaiian filefish, Orange-tailed filefish, ‘o’ili ‘uwi ‘uwi.

Scientific name: Pervagor spilosoma (Lay and Bennett, 1839).

Origin: The eastern side of the Pacific, particularly around Hawaii, but also sometimes from Fiji and French Polynesia.

Size: 14-17cm/5-7”.

Diet: Primarily algae and benthic invertebrates, including corals. As it’s fairly omnivorous it will adapt to frozen foods, unlike some other filefishes, which makes it not too challenging for the experienced marine fishkeeper. However, check that your dealer has got the fish feeding before buying. Feed them little and often with Mysis and brineshrimp.

Aquarium: Not to be trusted in the reef tank, so better off in a fish-only system with live rock, unless you’re creating a set-up in which you want the fish to graze on fast-growing corals.

Unless you can get a pair or have an exceptionally large tank, we’d recommend only going for a single specimen. Filefish aren’t thought to be capable of changing sex like other marine fish, so unless lucky you could end up with incompatible fish.

Breeding: This species has yet to be bred. However, the related Pervagor melanocephalus has been spawned but the fry yet to be raised. The author is now trying his hand at P. spilosoma, so there’s a chance this may happen.

Price: Around £14 each.

Ask the expert

New York filefish fanatic Dominic Cirigliano explains how he keeps his and how he recorded a successful spawning from the related Pervagor melanocephalus.

How do you keep your spilosoma? Do you have many in your marine tank, what size is it and do you have any inverts in there?

I have two spilosoma in the same tank. It is a community tank with other filefish, including Acreichthys tomentosus and Pervagor melanocephalus, and both are about 10cm/4” long. I keep them with a lot of live rock and open space. I did have them in a reef tank without affecting my corals, but they do eat ornamental shrimp and I never had any luck keeping any shrimp long-term. I mix their diet between frozen, live and pellet foods.

How do they get along with each other and with other species? Is it best to buy individuals, or can multiple specimens be kept together successfully?

I’ve kept them with many species of files (Acreichthys tomentosus, Pervagor melanocephalus, Chaetoderma pencilligera, Cantherhines sandwichiensis, Oxymonacanthus longirostris and Monacanthus tuckeri) without any problems. They sometimes battle over food, but that’s about it. I think that’s a direct relationship with the quantity of food and available space. I think keeping multiple specimens is fine, depending on the size of the system.

You’ve reported spawnings in other Pervagor. What happened and do you think you’re likely to eventually see similar things with your spilosoma?

The spawning of the melanocephalus was unexpected. I happened to catch the male and female together near a rock clearing out some sand and laying eggs.  All of my filefish have been noted spawning except my pencilligera, Stephanolepis hispidus and Monacanthus tuckeri. Hopefully I will have a similar experience with the spilosoma but I am still working on sexing them.

What do you feed yours and how easy are they compared to other filefishes?

Like most files (longirostris being an exception) they are pretty easy to get eating. Mine eat frozen Mysis, pellet foods, live grass shrimp and large amphipods. Occasionally I would offer cocktail shrimp and squid. Of the filefish I’ve kept, they are among the easiest to get eating.

Did you know?

  • The Hawaiian name for filefish is ‘o’ili’ which roughly translated means ‘makes a sudden appearance’, and refers to the amazing spawning spectacle these fish create every so often.
  •  The Fan-tailed filefish is more specifically known among Hawaiians as ‘o’ili ‘uwi ‘uwi’. The latter part means ‘squealing’ and refers to the squeaking noise they make with their swimbladder when removed from water.
  •  Apparently they’re not very tasty, but Hawaiians used to dry them and their oily flesh apparently makes good fuel for cooking tastier, less bony species.

This article was first published in the October 2009 issue of Practical Fishkeeping magazine. It may not be reproduced without written permission.