Cirrhilabrus isosceles is a slender Western Pacific fairy wrasse recorded from Izu-Oshima and the Ryukyu Islands south through Taiwan to the Philippines, typically between 24 and 60 meters over flat or gently sloping bottoms punctuated by low rock and scattered coral outcrops. Terminal-phase males are the showpiece: orange-yellow across the back, grading into lavender along the belly, with a vivid blue-to-purple lateral stripe and a dark mid-dorsal blotch. The elongated, broadly lanceolate tail carries the triangular color pattern that gave the species its name. Initial-phase individuals are more uniformly orange with muted striping. Adults reach roughly 4 inches.

Plan on an established marine system of at least 70 gallons, with the footprint weighted toward horizontal open water rather than height, since this is a fish that patrols the middle of the tank throughout the day. Secure the live rock so it forms stable caves and crevices for daytime retreat and nighttime shelter. A tightly fitted, gap-free lid is not optional; fairy wrasses jump, and this one is no exception. Medium flow and consistently stable water chemistry suit it well. Because it originates from deeper reef slopes, shaded overhangs and a gradual introduction to intense reef lighting help it settle. Reports on substrate preference disagree, with some accounts describing sand-burying behavior and others noting that fairy wrasses sleep in rockwork instead; well-structured rock with reliable hiding places is the requirement that holds up across the evidence.