The Marine Betta (Calloplesiops altivelis), also known as the Comet Fish or Marine Betta, is a species of marine ray-finned fish belonging to the family Plesiopidae. It was first formally described in 1831 by Georges Cuvier. The specific name altivelis means "high-scaled" in reference to the tall dorsal and anal fins.

Distribution and Habitat

The Marine Betta is widely distributed in the Indo-Pacific from the Red Sea and East Africa to the Hawaiian Islands and French Polynesia, north to southern Japan and south to northern Australia. It inhabits coral reefs and rocky substrates at depths from 3 to 50 meters. It is a secretive species that is typically found in caves and under overhangs during the day.

Physical Description

The Marine Betta reaches a maximum total length of 20 cm (7.9 in). The body is dark brown to black with numerous small white to pale blue spots covering the head, body, and fins. The most distinctive feature is the large ocellus or eyespot on the dorsal fin that resembles an eye. This false eye is believed to confuse predators about the direction the fish will flee. The dorsal fin has 11 spines and 8-9 soft rays while the anal fin has 3 spines and 9 soft rays. The caudal fin is rounded.

Diet and Feeding

The Marine Betta is a carnivorous predator that feeds on small fish and crustaceans. It is an ambush predator that waits in its cave for prey to pass by before darting out to capture it. In the aquarium it can be trained to accept frozen foods but initially may only accept live foods such as ghost shrimp and feeder fish.

Behavior and Reproduction

This species is solitary and nocturnal. During the day it remains hidden in caves and under overhangs. It is generally peaceful toward larger tankmates but will eat any fish or shrimp that fits in its mouth. When threatened it swims into its cave head-first, leaving the ocellus on its dorsal fin facing outward to mimic the head of a moray eel. Reproduction involves the male guarding a nest of eggs laid on the ceiling of a cave.

Aquarium Care

The Marine Betta requires a tank of at least 50 gallons with plenty of live rock and caves for hiding. It is generally reef-safe with caution as it will eat small fish and shrimp. It is compatible with larger peaceful fish. This species can be difficult to feed initially and may require live foods before transitioning to frozen foods. Water temperature should be maintained between 72-82 F (22-28 C) with pH 8.1-8.4 and dKH 8-12.

Conservation Status

Classified as Least Concern by the IUCN Red List.