Domino Damsel

, showing yellow colouration from D. auripinnis introgression.]] Dascyllus trimaculatus is one of four species in its namesake D. trimaculatus species complex. The other three species in this complex are D. albisella, D. strasburgi, and D. auripinnis. D. trimaculatus and D. auripinnis are parapatric (their ranges overlap in the Northern Cook Islands), but the four species are otherwise all allopatric. The D. trimaculatus complex diverged from the D. reticulatus complex 3.9 million years ago, in the Pleistocene. Mitochondrial genome analysis found that D. trimaculatus itself can be split into three populations: Indian Ocean, southern French Polynesia, and West-Central Pacific. D. auripinnis has been found to clade with the West-Central Pacific population of D. trimaculatus, which raises some doubts as to the former's validity. Fish described as D. trimaculatus in Fiji have yellow pelvic and anal fins, and streaks of orange in the dorsal and caudal fins. These physically appear intermediate between D. trimaculatus and D. auripinnis; genomic analysis shows that they are a result of introgression of D. auripinnis into D. trimaculatus through repeated backcrossing.

Trimaculatus, meaning "three-spotted", refers to the fish's three white spots. This accounts also for the common name "domino".

Like other species in the D. trimaculatus species complex, D. trimaculatus recognizes conspecifics using sound.

with a sebae clownfish.]]Juveniles dwell with anemones such as Stichodactyla mertensi for shelter. This relationship with anemones is lost as they mature into adults. On very rare occasions, the juveniles may use corals instead.

During the juvenile period, they live with the sea anemone. They grow fast and can grow up to in length in a large fish tank.