Yellow Flank Fairy Wrasse - Cirrhilabrus ryukyuensis

Yellow Flank Fairy Wrasse (Cirrhilabrus ryukyuensis)

The Yellow Flank Fairy Wrasse, Cirrhilabrus ryukyuensis, is a striking Western Pacific reef fish recognised by its vivid green-blue head, warm red to orange body and distinctive yellow patch behind the pectoral fin. Also known as the Ryukyu Fairy Wrasse or Blueside Wrasse, mature males develop the strongest contrasting colours, while females and juveniles display softer reddish tones. This active zooplankton feeder naturally swims above coral and rocky reef habitats in loose social groups. Its bright colouration and excellent coral compatibility make it a desirable addition to spacious reef aquariums with suitable tank mates and a completely secure cover.

Common Name:
Yellow-flanked Fairy Wrasse, Yellow Flank Fairy Wrasse, Ryukyu Fairy Wrasse, Blueside Wrasse, Yellow-sided Fairy Wrasse.

Scientific Name (Latin):
Cirrhilabrus ryukyuensis

Maximum Size:
Usually around 12–15 cm when fully grown, with mature males generally becoming larger and more strongly coloured than females.

Water Type:
Marine

Origin / Natural Habitat:
Western Pacific, occurring from Indonesia, Malaysia and the Philippines northwards through Taiwan to the Ryukyu Islands of southern Japan.

Yellow Flank Fairy Wrasses inhabit coral and rocky reef environments where they swim above reef structure while feeding on passing zooplankton. They remain close enough to caves and crevices to retreat quickly when threatened and may occur in loose social groups containing females, juveniles and a dominant male.

Water Parameters:
Temperature: 24–28°C
pH Range: 8.1–8.4
Hardness or Salinity: Marine salinity 1.023–1.026 specific gravity; maintain stable salinity, alkalinity, strong oxygenation and consistently high water quality.

Temperament:
Generally peaceful to moderately assertive. Yellow Flank Fairy Wrasses usually coexist well with confident community reef fish but may become territorial towards closely related Cirrhilabrus species or similarly coloured males.

Mature males can be more dominant than smaller or reserved fairy wrasses. Avoid keeping several similar males together unless the aquarium is exceptionally spacious and contains extensive visual barriers.

Diet:
Carnivorous zooplankton feeder. In the wild, this species feeds on copepods, small crustaceans and other planktonic organisms captured from the water column above the reef.

In the aquarium, offer enriched mysis shrimp, Artemia, copepods, Calanus, finely chopped krill, small marine pellets and high-quality marine flakes. Feed small portions at least twice daily to support its active metabolism and maintain good body condition.

Minimum Tank Size:
A minimum aquarium volume of approximately 300 litres is recommended for one adult, with a long swimming area and extensive mature rockwork. A larger aquarium is preferable when maintaining several fairy wrasses or a compatible social group.

Behaviour & Activity:
An active daylight-swimming wrasse that spends most of its time moving through the middle and upper areas of the aquarium while feeding from the water column.

Mature males may intensify their colours, spread their fins and perform rapid display swimming when interacting with females or rival wrasses. The yellow flank patch can vary in size and intensity between individuals and may be especially prominent in particular adult males.

At night, the fish retreats into a narrow rock crevice and may surround itself with a thin protective mucus cocoon. Unlike Halichoeres and leopard wrasses, the Yellow-flanked Fairy Wrasse does not normally bury itself in sand.

Reef Safe:
Reef Safe

Yellow Flank Fairy Wrasses do not normally damage corals, anemones, clams or established ornamental invertebrates. They feed primarily on small planktonic organisms in the water column and are well suited to mixed reef aquariums.

Very small planktonic crustaceans and larvae may be consumed as part of their natural diet, but established ornamental shrimps, crabs and snails are generally ignored.

Special Requirements or Care Notes:
A tightly fitted aquarium cover or fine mesh lid is essential because fairy wrasses are exceptionally capable jumpers. Cover all openings around cables, pipework, overflow boxes and feeding hatches.

Provide extensive secure rockwork containing caves and narrow sleeping crevices, alongside generous open swimming room. Moderate to strong, well-distributed water movement and excellent oxygenation suit this active reef species.

Introduce closely related fairy wrasses carefully and add the largest or most dominant male last where possible. An acclimation box can help assess aggression before release. Avoid keeping multiple mature males of similar size and appearance unless the aquarium is exceptionally large.

A social group should normally consist of one male with one or more females. Females of Cirrhilabrus species may transition into males when no dominant male is present, which can alter compatibility within an established group.

Newly introduced specimens may remain close to shelter for several days. Offer small foods near their retreat and avoid aggressive or exceptionally fast-feeding tank mates that could prevent them from eating.

Slow acclimation and quarantine are recommended. Monitor carefully for rapid breathing, external parasites, mouth damage, faded colour and loss of appetite following transport.

Suitable for:
Intermediate fishkeepers

Availability:
Rare or occasional in trade

All images are a visual representation of the fish you will receive, made to be as accurate as possible. Please note that Mother Nature is a wonderful thing, and variation in patterns and colours will occur — that is part of the unique beauty of these animals.