IntermediatePeacefulReef Safe with Caution

Marine Betta

Calloplesiops altivelis

Family: Plesiopidae · Oddball & Rare Fish

Also known as: Comet, Comet Grouper, Roundhead

Max Size

Min Tank

55 gal

Lifespan

5-10 years

Origin

Indo-Pacific, Red Sea

Diet

Carnivore

Swims

Middle

About

The Marine Betta is one of the most visually spectacular and unusual fish available to marine aquarists. Its elongated body and dramatically oversized, flowing fins are jet black and covered with a constellation of small white spots, giving it a comet-like or celestial appearance that is truly unlike any other aquarium species. A large false eyespot, or ocellus, is prominently positioned on the rear dorsal fin area, which plays a central role in the fish's remarkable defensive mimicry strategy.

When threatened, the Marine Betta retreats headfirst into a crevice, leaving its spotted rear end and prominent false eyespot exposed. This display closely mimics the head of a White-Mouth Moray Eel (Gymnothorax meleagris), which shares a similar spotted pattern. Predators approaching the Marine Betta from behind are confronted with what appears to be the face of a much larger, dangerous eel, causing them to retreat. This is one of the most elegant examples of Batesian mimicry in the marine world and is regularly observed in the aquarium setting.

In the aquarium, the Marine Betta is a shy, nocturnal predator that requires patience during the acclimation period. It often hides for the first several weeks and may initially refuse prepared foods, requiring live ghost shrimp or small feeder fish to stimulate feeding. Once acclimated, most specimens learn to accept frozen silversides, mysis shrimp, and other meaty foods. It is peaceful toward fish too large to swallow but will readily consume small shrimp and very small fish. The Marine Betta does best in a dimly lit aquarium with ample caves and overhangs, and it becomes more visible and bold over time as it learns to associate its keeper with food.

Feeding & Diet

Carnivore

Marine Bettas are carnivorous ambush predators that feed on small fish and crustaceans. In captivity, they may initially require live ghost shrimp or small feeder fish before being weaned onto frozen foods. Offer frozen silversides, mysis shrimp, krill, and enriched brine shrimp. Feed every other day once established. Use feeding tongs to target-feed if necessary.

Compatibility

reef-cautionpeacefulpredatornocturnaloddballmoray-mimic

The Marine Betta is peaceful toward fish too large to swallow but is a stealthy predator of small fish and shrimp. Compatible with medium to large community fish including tangs, angelfish, larger wrasses, and clownfish. Avoid housing with small gobies, firefish, or ornamental shrimp. Best added to the tank before more aggressive species to give it time to establish territory.

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Breeding

Difficult

Marine Bettas have been bred in captivity, though it remains uncommon. They are secretive cave spawners, with the male guarding a large egg mass deposited on the ceiling of a cave. The male does not eat during the incubation period, which lasts approximately five to six days. Larvae are pelagic and require rotifers and copepod nauplii as first foods.