Blue Assessor

The Blue Assessor is a small, secretive reef fish admired for its uniform deep blue to purple-blue coloration and its remarkable habit of swimming upside down near cave ceilings and overhangs. This unusual inverted swimming behavior is not a sign of distress but rather a natural adaptation that allows the species to remain close to sheltered surfaces while maintaining visual contact with the surrounding water column for passing zooplankton prey. The effect is mesmerizing to observe, as the fish appears perfectly at ease gliding belly-up beneath ledges.

In the wild, Blue Assessors inhabit shaded reef caves and crevices along Australia's eastern coastline, typically at depths between 15 and 40 meters. They are usually encountered singly or in loose pairs, hovering just inside cave mouths where they can quickly retreat if threatened. Their deep blue coloration helps them blend into the shadows, and they rely on their cryptic behavior and cave-dwelling lifestyle to avoid predators. Despite their shy disposition, they are curious fish that will gradually become bolder over time in a well-maintained aquarium.

The Blue Assessor is an excellent choice for peaceful reef aquariums, particularly nano systems of 20 gallons or more. It is completely reef-safe, ignoring corals and all invertebrates. Its shy nature means it should be housed with other gentle, non-aggressive species, and it requires plenty of caves and overhangs to feel secure. Once settled, it will spend much of its time hovering at the entrance of its chosen cave, swimming right-side-up or inverted with equal ease. Captive-bred specimens are sometimes available and are recommended for their improved hardiness and willingness to accept prepared foods.