Why is my new McCosker's Wrasse always hiding?

Flasher wrasses can be very timid when first introduced, especially if there are larger or more active fish in the tank. Provide plenty of hiding spaces and ensure peaceful tank mates. They usually become bolder after a few days once they realise there is no threat.

Do I need to keep them in a harem?

No, a single male will thrive entirely on his own. However, keeping one male with two or three females will encourage his natural 'flashing' behaviour, as he will display to them daily.

Will McCosker's Wrasses eat my ornamental shrimp?

They are completely reef-safe and have very small mouths adapted for eating microscopic zooplankton. They pose absolutely no threat to cleaner shrimp, peppermint shrimp, or corals.

Why is my male flasher wrasse losing his bright colours?

Colour loss can occur due to a lack of dietary variety, poor water quality, or the absence of females to display to. In a tank with a more dominant male flasher or fairy wrasse, a submissive male may intentionally dull his colours to avoid aggression.

How do I stop my flasher wrasse from jumping?

You cannot train them out of this instinct. A perfectly fitted mesh or glass lid is completely mandatory for this species, as they will inevitably jump when startled by lights or other fish.

MarineMarineIntermediate

McCosker's Flasher Wrasse

Paracheilinus mccoskeri

A brilliantly coloured, peaceful reef fish famous for the male's spectacular, fin-flaring courtship displays.

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Ideal Conditions

Temperature: 23 – 27 °C
pH range: 8.1 – 8.4
Hardness: 8 – 12 dGH
Salinity: 1.023 – 1.025 SG
Adult size: 7 – 8 cm
110L minimum for a single male, 200L+ for a harem: 110 litres+
Lifespan: 5 – 8 years
Diet: Carnivore/Planktivore
Water flow: Moderate
Preferred setup: Reef environment with plenty of open swimming space and scattered rubble or live rock hiding places.

About the McCosker's Flasher Wrasse

The McCosker's Flasher Wrasse is an exquisite, small-bodied marine fish that brings vibrant movement to the reef aquarium. They belong to a group known as 'flasher wrasses', named for the male's remarkable ability to instantly intensify his colours and erect his fins in a dazzling display to attract females or intimidate rivals. As a predominantly Indian Ocean species, it features a distinct morphology—most notably, the male possesses a single elongated filament on his dorsal fin. Their small size and minimal impact on the biological load make them highly sought after by reef enthusiasts.

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Is it right for your tank?

Check McCosker's Flasher Wrasse against a habitat you already keep. We compare water type, temperature, pH, adult size, group needs and everything living there.

Where McCosker's Flasher Wrasse comes from

Native range

Indian Ocean, Andaman Sea

Countries / regions

Kenya, Maldives, Indonesia

Habitat

Found over rubble zones, sheltered patch reefs, and steep outer reef slopes, typically at depths between 10 and 50 metres.

Primarily an Indian Ocean species, its range extends from the east coast of Africa across to the western reaches of Indonesia.

Similar species

Carpenter's Flasher Wrasse
Paracheilinus carpenteri
Filamented Flasher Wrasse
Paracheilinus filamentosus
Exquisite Fairy Wrasse
Cirrhilabrus exquisitus

We’re adding more full species guides as the catalogue grows.

Compatible tank mates

Reviewed guidance based on this species' recorded traits.

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Ocellaris Clownfish
Amphiprion ocellaris
Peaceful and occupies a different area of the reef tank; neither will bother the other.
Great
Firefish Goby
Nemateleotris magnifica
A similarly sized, peaceful planktivore that makes an excellent companion in a quiet community.
Great
Cleaner Shrimp
Lysmata amboinensis
McCosker's Wrasses have very small mouths and pose no threat to ornamental shrimp or other reef invertebrates.
Great
Carpenter's Flasher Wrasse
Paracheilinus carpenteri
Congeneric males may fight fiercely over territory and females in standard-sized aquariums.
Compatible with caution
Sixline Wrasse
Pseudocheilinus hexataenia
Often far too aggressive and territorial, capable of harassing the more timid flasher wrasse to death.
Not recommended
Royal Dottyback
Pictichromis paccagnellae
Highly territorial and aggressive; will easily intimidate and outcompete the peaceful McCosker's Wrasse.
Not recommended

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