Moorish idol

Care at a glance

Overview

Moorish idols are peaceful, almost timid fish that rarely bother tankmates, and they're reef safe only with caution, since they'll graze on coral polyps and zoanthids along with the sponges and algae they need most. The honest problem is survival, not temperament: this is widely considered the hardest commonly sold marine fish to keep alive, with roughly 80–90 percent of imported fish dying within their first year, most within the first month, almost always because they refuse to eat in captivity. Most hobbyists, even experienced ones, are better off enjoying this fish on the reef or at a public aquarium instead of attempting it at home; anyone who does try needs an established tank loaded with natural sponge and algae growth, live rock, and a long list of foods on hand before the fish ever arrives.

In the wild

Moorish idols range across nearly the entire Indo-Pacific, from East Africa and the Red Sea to Hawaii and Easter Island, and even turn up in an isolated eastern Pacific population from the Gulf of California to Peru. They live on reef flats and seaward reefs, usually alone, in pairs, or in small groups of two or three, occasionally gathering into much larger aggregations to spawn. In the aquarium it needs a long, open tank of at least 473 litres (125 US gal) with mature live rock carrying a real growth of sponges and algae, since that natural food source matters more to this fish's survival than almost anything else in the setup.

Good to know

Zanclus cornutus is the only species in its family, Zanclidae, easily told apart from surgeonfish and butterflyfish by its long, sickle-shaped dorsal fin and small, bristly-toothed snout built for picking food out of tight crevices. In the wild, sponges make up roughly 70 percent of its diet, rounded out with algae, tunicates, and small amounts of coral polyps. Its larvae drift in the open ocean for around 70 days before settling on a reef, an unusually long pelagic stage that explains how the species ended up so widely spread across the Pacific and Indian Oceans.

Common questions

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