Yellowback anthias

Geographical Origin and Habitat: Mirolabrichthys evansi is native to the tropical Indian Ocean, with a distribution range extending from the East African coast (including Mauritius and the Seychelles), through the Maldives and Chagos archipelagos, to the Cocos-Keeling Islands. It inhabits outer reef slopes and steep drop-offs exposed to strong currents, at depths between 4 and 30 meters. They aggregate in large schools hovering above hard branching Acropora corals, which provide immediate shelter.

Taxonomy and Morphology: It belongs to the family Serranidae and the subfamily Anthiadinae. It features a slender, streamlined, and elongated body with a large eye and protractile mouth. The caudal fin is deeply bifurcated (lyre-shaped) and features long filaments extending from the lobes in adult males. The fins are adapted for continuous swimming against strong currents. It reaches a maximum length of about 10-12 cm.

Social Behavior: It is a highly gregarious and social species characterized by a complex hierarchical structure within the shoal. Like all anthias, it is a protogynous hermaphrodite: individuals are born female and transition into dominant males based on social cues. In captivity, they must be kept in a small harem consisting of one male and several females. They spend the day actively swimming in the water column looking for food.

Coloration and Sexual Dimorphism: Its coloration is spectacular and unique: the body displays a bright pinkish-purple or magenta color on the flanks and belly, which transitions sharply to a bright golden yellow on the back, dorsal fin, and upper caudal lobe. Sexual dimorphism is distinct: males feature more intense coloration, longer caudal filaments, and a characteristic yellow or red stripe running from the eye to the pectoral fin base.

Aquarium Setup: Requires a mature and spacious marine aquarium of at least 250-300 liters to house a small group. The layout should feature a large open swimming area in the center, supported by a rockwork structure containing caves, overhangs, and shaded spots for shelter. Strong water movement created by wavemakers is essential to simulate the currents of their natural outer reef slope habitats.

Diet and Feeding: This is the most critical factor for their survival. Wrasses of this species are specialized zooplanktivores with a very high metabolic rate. In the aquarium, they must be fed frequently (at least 4-5 times a day) with small amounts of high-quality frozen foods like copepods, rotifers, baby brine shrimp, mysis, and lobster eggs. Inadequate feeding frequency leads to rapid weight loss and death.

Water Quality: Demands pristine and highly stable water parameters: temperature 22-26 °C, pH 8.1-8.4, specific gravity 1.020-1.025, and KH 8-12. An efficient filtration system with an oversized protein skimmer and regular water changes are necessary to keep nitrates and phosphates close to zero, while ensuring high dissolved oxygen saturation levels.

Compatibility and Cohabitation: It is 100% reef-safe and will not bother corals, clams, or invertebrates. It is a peaceful, easily stressed fish that must only be housed with docile reef species like gobies, clownfish, and small wrasses. Avoid keeping them with large, fast-moving, or aggressive tankmates that could intimidate them and prevent them from emerging from the rockwork to feed.

Aquarium Breeding: Breeding in home aquariums is extremely difficult, and no successful spawnings have been reported. In the wild, they are pelagic spawners, releasing eggs and sperm into the water column at dusk. Rearing the larvae requires specialized setups and a constant supply of specific live micro-plankton, which is difficult to cultivate.

Risks and Diseases: They have an extremely high mortality rate during the first few weeks due to shipping stress and starvation. They are highly susceptible to marine parasites like marine ich (Cryptocaryon) and velvet if stressed. A quarantine period is strongly recommended to monitor their health and acclimate them to frozen food before introducing them to the main reef tank.