Blue Assessor

About

The blue assessor (Assessor macneilli) is one of those fish that immediately raises questions from anyone who sees it for the first time, because it spends much of its time cruising along cave ceilings and overhangs with its belly pointing upward. That inverted swimming posture is completely normal for this species and is part of what makes it so fascinating to watch in a reef tank. It's a small, slender basslet with a vivid blue coloration that holds up well under aquarium lighting, and it tends to stay fairly compact, making it suitable for modestly sized reef systems. In the wild it's closely associated with caves, ledges, and shaded reef structures where it can hover in dim, sheltered spots. This habit carries over directly into captivity, so giving it plenty of rockwork with overhangs and caves is important for keeping it comfortable and secure. The blue assessor is generally peaceful toward other tankmates and can often be kept in small groups if the aquarium has enough territory, though pairs or trios tend to work better than crowding multiple individuals into a tight space. It's not the easiest fish to acclimate, and getting it to accept prepared foods consistently takes some patience, which is why intermediate experience is worth having before adding one to your system.