Six-Line Wrasse | Marine Species

Six-line wrasse（圖片來源：Brian Gratwicke，採用 CC BY 2.0 授權）

The six-line wrasse (Pseudocheilinus hexataenia) is a small member of the wrasse family (Labridae) native to tropical waters of the Indo-Pacific. Its distribution extends from the Red Sea and the eastern coast of Africa across the Indian Ocean and into the Pacific, reaching as far as the Tuamotu Archipelago in the South Pacific. The species occupies a very wide geographic range. In Australian waters it can be found from northern Western Australia throughout the Great Barrier Reef and southward to the northern coast of New South Wales.

Although this species rarely exceeds 10 cm in length, it is highly recognizable due to its striking coloration. The body displays a purplish-blue base color with six vivid orange-red horizontal stripes along the sides. Near the caudal peduncle there is a dark eyespot bordered with blue, while the caudal fin appears greenish with a bluish sheen. The eyes are bright red and crossed by two white lines, producing a strong visual contrast. This distinctive coloration is not only visually attractive but may also help confuse potential predators.

In the wild, the six-line wrasse commonly inhabits outer reef slopes, reef crests, and areas among branching corals. It typically occurs in shallow waters at depths between about 2 and 30 meters. These fish are naturally shy and cautious. When startled, they quickly retreat into coral crevices for protection. They are active during the day, while at night they construct a mucous cocoon inside rock crevices or among coral branches, enveloping their bodies in a thin layer of mucus. This cocoon helps conceal their scent and reduces the chance of detection by nocturnal predators. Such “sleeping cocoons” are characteristic of many wrasses. Unlike some wrasse species that bury themselves in sand, the six-line wrasse relies on this cocoon combined with shelter within reef structures.

The six-line wrasse is carnivorous, feeding primarily on small crustaceans, amphipods, and fish eggs. It may also occasionally function as a cleaner fish, removing parasites from larger fishes. Because it feeds by searching carefully among reef surfaces and coral branches, the fish frequently moves through the reef structure with agile and precise movements. In nature the species often lives in small groups, typically consisting of a single male accompanied by several females. The species exhibits protogynous hermaphroditism, meaning individuals first mature as females. If a group lacks a male, one of the females may transform into a male and assume the reproductive role. Spawning generally occurs shortly before sunset, when a male and female rapidly swim upward in the water column to release eggs and sperm, allowing the fertilized eggs to drift away with ocean currents.

Although small, the six-line wrasse possesses a strong personality and often displays territorial behavior. It may show aggression toward closely related species or fish of similar size. In natural habitats the fish may appear timid, yet it will actively drive away intruders when necessary to defend feeding and breeding space.

Six-line wrasse（圖片來源：Diego Delso，採用 CC BY-SA 4.0 授權）

Housing Requirements in Captivity

In aquarium settings, the six-line wrasse is considered a relatively hardy marine ornamental fish. Its small body size means it does not require extremely large aquaria, yet a tank volume of at least 100–200 liters is recommended, while systems exceeding 400 liters can further reduce territorial stress. The aquarium should contain abundant live rock and reef structures that allow algae growth and create numerous crevices and caves. These structures provide essential hiding places. Without adequate shelter, the fish may experience stress and become more aggressive or refuse food.

Water conditions should remain stable. Suitable temperatures range from 23 to 27°C and should not remain outside this range for extended periods. Salinity should be maintained between 30‰ and 35‰, while pH is best kept between 8.0 and 8.5. Nitrate levels should remain below 50 mg/L. Regular water changes of about 20–30% each month are recommended to maintain water quality. Some aquarists use systems such as the Jaubert method or nitrate-reduction devices to assist in controlling nitrate levels and improving stability.

Six-line wrasses are skilled jumpers. Aquaria must therefore be fitted with a secure lid to prevent them from leaping out when startled or during rapid movements. Compatibility with other aquarium inhabitants can be unpredictable. The species may bully slower or more timid fish, especially other wrasses or species with similar body shapes. For this reason, it is generally recommended that the six-line wrasse be introduced last when stocking a mixed aquarium so that it does not establish a dominant territory early on. Regarding invertebrates, most corals can coexist with this species, but small crustaceans such as shrimps and small crabs may become targets of attack or predation, so tankmates should be chosen carefully.

Feeding Conditions

In the wild, the six-line wrasse feeds mainly on small crustaceans and benthic invertebrates. Therefore, animal-based foods should form the primary diet in captivity. Common food items include brine shrimp, mysids, amphipods, finely chopped fish meat, shrimp pieces, or clam meat, all of which provide necessary protein and nutrients. Because the species feeds by continuous foraging rather than consuming large meals at once, it is best to offer food in small portions once or twice daily rather than providing a large amount at a single feeding, which may degrade water quality.

After acclimating to aquarium conditions, the six-line wrasse often accepts prepared foods such as flake foods or high-quality pellets. However, relying on a single food source may lead to nutritional imbalance, so maintaining a varied diet is important for long-term health. Some aquarists keep this species because of its predatory behavior toward certain aquarium pests, including parasitic snails. Nevertheless, this should not be considered its sole food source. If natural prey within the tank becomes insufficient, additional feeding is necessary.

Care should also be taken to avoid excessive competition during feeding. Six-line wrasses are quick and agile and often reach food first, which may create stress for slower fish species in the same tank. Distributing food across different areas of the aquarium can help ensure other fish also have opportunities to feed.

Breeding Conditions

Successful captive breeding of the six-line wrasse has not yet been consistently achieved. In natural habitats, a male typically maintains mating relationships with several females and spawning occurs during rapid upward swimming at dusk. Replicating this behavior in aquaria is difficult for several reasons. The species' strong territorial behavior makes maintaining multiple individuals challenging, and the eggs are pelagic, drifting freely in the water column after spawning. In aquarium systems, these eggs are easily removed by filtration equipment or consumed by other fish.

Another major difficulty lies in the extremely small size of the larvae. In the wild they feed on planktonic organisms, requiring highly specialized food sources that are difficult to provide in captivity. As a result, breeding success remains very rare.

For most aquarists, observing courtship or spawning behavior is already an interesting experience. Attempting artificial incubation is generally unnecessary, and it is often sufficient simply to appreciate their natural reproductive behavior.

Preventing Invasive Spread

Because of its bright coloration, small body size, and potential ability to control certain aquarium pests, the six-line wrasse is highly popular in the aquarium trade. However, if owners abandon or release captive individuals into non-native waters, ecological risks may arise.

Although waters around Taiwan fall within the natural distribution of this species, Article 32 of the Wildlife Conservation Act states that wildlife kept in captivity may not be released without approval from the competent authority. Additionally, diseases present in aquarium systems could spread to wild populations. Aquarium keepers should therefore follow the principle of not abandoning or releasing captive animals.

If an owner can no longer keep the fish, alternative solutions should be sought, such as transferring it to another aquarist or asking a nearby marine aquarium store whether they can accept it. Releasing aquarium animals into the wild should never be considered an option. Appreciation and care of the six-line wrasse should be based on a responsible attitude toward natural ecosystems, preventing ecological harm caused by careless disposal.

Furthermore, most six-line wrasses sold in the aquarium trade are captured from wild populations. When purchasing one, buyers should ensure that the source is legal and should avoid supporting unsustainable harvesting of wild populations.

Author: Shui-Ye You