Not furry, but we like them anyway.
Marine Betta
Calloplesiops altivelis
Also called Comet, Sea betta, Comet grouper
From Indo-Pacific, from the Red Sea and East Africa east to Tonga and the Line Islands1
At a glance the quick version
Looks how to spot one
Deep-bodied fish with very large, flowing fins
A dark brownish-black fish covered in tiny pale blue to white dots, with huge, rounded fins that flow like a cape. A blue-ringed black eyespot sits near the back of the dorsal fin, and there are yellowish spots at the top of the tail base.13
Personality what they are like
Calm, patient and peaceful toward fish too large to eat. It is a stalking predator by nature, so small fish and shrimp are best kept elsewhere.32
Daily activity how busy a day looks
Nocturnal. It rests in caves and under ledges by day and becomes more active around dusk and at night.123
Grooming and care the hands-on bits
Provide shaded caves and hiding places away from bright light. Live foods may help a newcomer start eating; once settled it usually takes meaty frozen foods 2 to 4 times a week.32
Home where they are happiest
Minimum about 50 US gallons (189 L) with caves and dim hiding spots. Saltwater at about 22 to 26 °C (72 to 78 °F), pH 8.1 to 8.4, dKH 8 to 12, specific gravity 1.020 to 1.025.3
Food basics what goes in the bowl
Carnivore. Wild fish hunt small fish and crustaceans; in the aquarium offer meaty and frozen preparations.23
Company who they like around
Usually kept singly with peaceful tankmates that are too big to be eaten and not so fast that they outcompete it at feeding time.32
The story where it all began
Franz Steindachner described the species in 1903 as Plesiops altivelis. J.L.B. Smith later described the same fish as Barrosia barrosi in 1952, a name now treated as a synonym. It has been bred successfully in captivity.2
Fun facts for the dinner table
- 1
When it feels threatened it pokes its head into a hole and leaves its tail end showing, which looks remarkably like a moray eel's head.1
- 2
The blue-ringed eyespot on its dorsal fin works as a false eye that helps confuse predators.1
- 3
It hunts by slowly drifting up to prey sideways and then waiting for it to make a move.2
- 4
Individuals have lived more than 8 years in captivity.1
- 5
It ranges across a huge area, from the Red Sea all the way to the Line Islands in the central Pacific.1
Recognised by the official bits
- IUCN Red List
- Least Concern (assessed 2019)1
The care rhythm Furry Diary remembers it for you
A typical home-care rhythm for a Marine Betta. It is our own starting plan, not a vet's advice, and you can change every line in the app.
- FeedingSmall amounts once or twice a dayevery day
- Temperature checkevery day
- Salinity checkevery week
- Top-upTop up evaporation with fresh RO water, not salt waterevery day
- Water testevery week
- Water changeAbout 10 to 20% of the waterevery 2 weeks
- Glass cleanevery week
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Where this comes from
Every breed page shows where each fact comes from. If we got something wrong, sorry, we are pet people, not a science magazine. Tell us at support@furrydiary.app and we will fix it.
- FishBase: Calloplesiops altivelis summary fishbase.seused for origin, size, colour, behaviour, mimicry, lifespan, IUCN
- Wikipedia: Calloplesiops altivelis en.wikipedia.orgused for history, other names, hunting, diet, captive breeding
- LiveAquaria: Marine Betta liveaquaria.comused for care, water parameters, tank size, diet, temperament
Checked 2026-09-30. Text is written in our own words from these sources.