Randall's Assessor Basslet (Assessor randalli)

Randall's Assessor shares the same upside-down habit as the Royal Gramma — both orient to the cave ceiling rather than to gravity, a trait called thigmotropism that keeps them tucked against a surface and out of open water where predators can pick them off. Deep electric blue from nose to tail, it schools loosely under overhangs in the wild and does the same in a tank with enough cover.

Care level: Easy · Temperament: Peaceful · Max size: ~2.5" · Min tank: 20 gal, with caves/ledges · Diet: Carnivore, meaty foods