Brittle stars in a reef tank

Quick reference

What are brittle stars?

Brittle stars are echinoderms with a small central disc and long, flexible arms. The ones most reefers meet are hitchhikers. Ophiactis savignyi, for example, has a disc about 5 mm across, usually six slender arms when young, and lives under rocks, in crevices and in sponges at very high densities; small ones reproduce by splitting the disc in two, each half regrowing the rest, so a tank can fill with clones.^[1] It's a deposit feeder, gathering particles with its tube feet.^[1]

Feeding

Hitchhikers need nothing extra. A green brittle star eats leftover food, algae, small invertebrates and detritus; Quality Marine recommends supplemental meaty foods such as krill or chopped prawn once or twice a week.^{[3, 2]} Some hobbyists report that regular feeding reduces attacks on tankmates, but Kurtz doesn't treat that as a guarantee.^[2]

Aggression and spacing

The green brittle star actively hunts. Kurtz describes it propping itself up on its arms with its disc raised, waiting for a fish to swim underneath, then dropping and wrapping it in its arms, usually at night.^[2] Quality Marine says a small fish or shrimp that hides under it can be caught and swallowed whole.^[3]

Tankmates

Kurtz calls the green brittle star technically reef safe with corals and other sessile invertebrates.^[2] Avoid small fish, especially bottom-dwellers such as gobies, ornamental shrimp and decorative clams; large triggers, tuskfish and puffers will eat the star.^{[2, 3]} Quality Marine advises against copper medications.^[3]

Troubleshooting

Common mistakes

• •Buying a green brittle star for a tank with gobies or small shrimp.^{[2, 3]}
• •Removing harmless hitchhiker brittle stars.^[1]
• •Keeping a green brittle star with clams.^[3]

Equipment & food for this species

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Inverts need stable salinity — use a refractometer, not a hydrometer.

Brittle stars FAQ

Are brittle stars good for a reef tank?

The small hitchhikers are: Ophiactis savignyi is a deposit feeder that eats detritus.^[1] The green brittle star is reef safe with corals but eats small fish.^[2]

Do green brittle stars eat fish?

Yes. Kurtz describes it trapping fish under its raised disc at night, and Quality Marine says it swallows small fish or shrimp whole.^{[2, 3]}

Why do I have so many tiny brittle stars?

Small Ophiactis reproduce by splitting in half and regrowing, forming clonal groups.^[1]

How big do green brittle stars get?

About 20 inches across the arms, with a disc of more than 2 inches.^{[2, 3]}

What size tank does a green brittle star need?

Quality Marine says 40 gallons or more is better than the 10 a single well-fed adult could survive in; Kurtz suggests 50 for a large one.^{[3, 2]}