Very few fish show sexual dimorphism, out of those few the Watanabei Angelfish, Genicanthus watanabei, is one of them. Both males and females have the same pale blue body color with black lining along the upper and lower fins. The difference in the sexes here is that the female has black blotching on the face and black outlines on the tail with no stripes on the body, whereas the male lacks this black blotching on the face and instead displays several horizontal blacks lines on the lower half of the body and no black on the tail. Since they are more peaceful than many other Angelfish, they can be kept as a mated pair, or in a small school of females. Avoid keeping two males in the same tank, as it can lead to extreme aggression.

These Angelfish are also unique in the way that they are reef safe, and will not nip at soft and stony corals, or sessile invertebrates, making them a great choice for an Angelfish in a reef tank setting. Diet should include a variety of spirulina, marine algae, high quality angelfish preparations, mysis and brine shrimp, 3 times daily.