UNARMED PERCHLET (PLECTRANTHIAS INERMIS)

Do you have an unarmed perchlet in your tank yet? WHAT ARE YOU WAITING FOR?? Photo by Scott W. Michael.

There are a number of fish species that have become quite common in the aquarium trade in the last six years. One of these, that I am most excited about, is an aberrant member of the subfamily Anthiinae. That’s right – it, and its kin (i.e., other members of the genus Plectranthias), are freaks of the subfamily. Most of the anthias spend the daylight hours in the water column, snapping up zooplanktors. But the freaky little perchlets behave more like hawkfishes (family Cirrhitidae) than their anthias relatives (so much is their likeness to a cirrhitid, that P. inermis is often sold in the aquarium hobby as the “geometric hawkfish.”) Rather than soaring about, high in the water column, they spend their time in repose on the seafloor. The are very cryptic, hiding among coral rubble or among stony coral branches during the day. These little fishes are often most active at dusk and dawn, or in dimly-lit microhabitats, like on rubble-covered cave bottoms or in the shadow of reef overhangs.

The unarmed perchlet (Plectranthias inermis) is a small fish, attaining about 5 cm in total length, that is ideal for the nano-reef aquarium. It is a threat to small ornamental shrimp (e.g., anemone shrimp), but otherwise, your prized invertebrates will be safe in the perchlet tank. It is also a threat to small gobies (e.g., Eviota, Trimma, Trimmatom). As far as its piscine neighbors are concerned, P. inermis is best housed with small, passive fish species (smaller cardinalfishes, small wrasses, blennies, dragonets, gobies, dartfishes). Its diminutive stature also means it a potential meal for large fish-eaters and a target of benthic bullies (e.g., dottybacks, hawkfishes).

There are over 40 species in the genus, many of which would make fascinating aquarium inhabitants. This is one of the most spectacular members of the genus, Pelicer's perchlet (Plectranthias pelicieri). It is rarely collected and those specimens that are go to the Japanese ornamental fish trade. Photo by Tsuyoshi Kawamoto.

More than one unarmed perchlet can be kept in a medium to large aquarium. However, males may fight (males, in general, are larger than females). Before making its approach toward a conspecific, P. inermis will raises and lower its elongated dorsal spine. If aggression escalates, the assailing perchlet will skim over the bottom as it approaches its adversary, with its tail slightly higher than its head. It undulates its tail, apparently to move itself forward, and spreads its gill covers (primarily the lower portion of the buccal area). All the fins are spread. I have noticed that as these fish grow, the pectoral fins become larger in proportion to the body size. Although studies are lacking, it is likely the Plectranthias spp. are protogynous hermaphrodites like other members of their subfamily.

The unarmed perchlet can be quite secretive, but will spend more time in the open in an aquarium that contains dither fish species such as Chromis, flasher wrasses, forktail blennies. It is prone to jumping, especially from tanks without adequate shelter and hiding places. Remember, is natural tendency is to lurk within rocky hiding places, resting at the entrance of a shelter and making a brief forays into the open. Provide it with nooks, crannies and caves.

This is the only member of the genus that I have encountered in the trade, although I continue to hunt!

Copyright (2008) Scott W. Michael