Yellowtail Coris

The yellowtail coris is one of the wrasses with the most striking color change between the juvenile and adult stages. Juveniles sold in stores are orange-red and carry large, black-edged white saddles on their backs. As they grow, the body turns dark blue-green and brown and fills with bright blue spots; the tail becomes bright yellow, and green and orange lines appear on the head. It is a relative of the Mediterranean rainbow wrasse (Coris julis).

The small, cute juveniles turn into a greedy, rock-toppling fish that reaches 40 cm as an adult; it is not suitable for a small reef aquarium. All individuals are wild-collected.

It lives on Indo-Pacific reefs in places with a mix of sand, rubble and rock. It hunts crabs, snails and worms by flipping over stones; at night and when in danger it buries itself in the sand.

• Volume: at least 600 liters and 180 cm of length for an adult.
• Sand: a fine-grained sand bed at least 5–8 cm deep is essential; it sleeps buried in it.
• Lid: it jumps; use a sturdy lid.
• Water: salinity 1.023–1.026 specific gravity, pH 8.1–8.4, temperature 24–27°C.
• Reef compatibility: not reef safe. It eats shrimp, crabs, snails, sea urchins and worms; it topples small rocks and coral fragments. Rocks should be secured.

Carnivorous. Frozen mysis, krill, chopped shrimp, mussel and squid, and marine fish granules. Juveniles are fed 2–3 times a day, adults 1–2 times a day. Hard-shelled foods such as shell-on shrimp and small mussels support natural hunting behavior. Because it constantly stirs up the sand while searching for food, a very fine sand bed can cause cloudiness; a powerful mechanical filter balances this out.

Juveniles are relatively docile; adults are bold, active and sometimes cranky. It attacks its own kind and similar wrasses. Very small fish that fit in its mouth are also at risk.

Good companions: in a large aquarium, tangs, large angelfish, foxface, Heniochus, large damsels, calm triggerfish.

Avoid: reefs with shrimp, snails and crabs; small and timid fish; a second large wrasse.

Keep a single individual in the aquarium. In the wild, loose groups of one male and several females are seen.

A wrasse that starts out as a female (protogynous); the dominant individual changes into a male. Male and female rise into the water column and release pelagic eggs. It does not breed in the aquarium.

• Marine ich and velvet: new fish should be observed in quarantine.
• Skin wounds: caused by burying itself in sharp gravel.
• Jumping: a common cause of loss in an uncovered aquarium.

The sex of juveniles cannot be told. Among adults, the dominant individual that changes into a male is the largest in the group and has more intense colors.