The comet or marine betta (Calloplesiops altivelis) is a species of reef-associated tropical marine fish in the longfin family Plesiopidae, most commonly found between 3 and 50 m deep.

The comet is nocturnal by nature, and will hide under ledges and in holes by day.

During night time, it leaves its hiding place and swims along the reef searching for food.

[4][5] Comets are known to be difficult to feed in captivity, as they will generally only accept live foods.

Therefore, if they are in an aquarium with other predatory fish (e.g. lions and groupers), they might starve, as they are not fast enough to get a good share of the food.