There is a beautiful grace the peaceful Marine Betta (Bet’-ah) has, and now it is available as a tank bred fish! 

The Marine Betta is a dark brownish black with numerous small white dots on the body area.  They have very large and exaggerated fins, similar to the shape you see when a freshwater betta gets angry.  As the dots move into the fins they turn more of a pale blue and then start to form thin blue lines on the dorsal and anal fins.  Those fins, in large specimens form a bright blue and orange edging.  Their pectoral fins are clear, but the rays are bright yellow.  Newborns are dark then develop a have a very large white area on each side of their bodies which shrinks in size as the fish grows, disappearing at 7 months.  They have an “eye spot” which is a black spot edged in pale blue which a little yellow at the bottom edge, which confuses both predators and prey!   The Marine Betta grows to 7.8” (20 cm) in the wild, but typically only grow to 7” in captivity.  While newly acquired wild caught need live foods, fully acclimated fish are perfect for beginners.  

This fish comes from the family Plesiopida which consists of assessors, fairy basslets, devilfish and longfins.  The family is referred to as the Longfins or Roundheads.  The Marine Betta is not a grouper or soapfish, though it does have similar patterning as members in both of those families.  This family, including the Marine Betta are very cryptic fish and are seldom seen on the reef due to their mad skills at hiding!  Daylight is avoided.  Even spawning has not beed observed in the wild.  In captivity, they are finally being tank bred!  As of December 2012, baby Marine Betta have become available to fish stores!  The coolest thing they do is when they are hunting.  They tip their body forward, head lowered, spread their pectoral fins and curl their tailfin which is ultimately used to propel them into the prey.  The false eye spot confuses the prey and the fish typically ends up running away from the “scary black false eye” into the scary “invisible” mouth!  If there is a predatory fish after them, they will go into a crevice head first, leaving their back half out and pose in a way, using their unique patterning,  to mimic a White Mouthed Moray Eel (Gymnothorax meleagris).  Most fish won’t mess with a Moray Eel and swim away!  

The wild-caught juvenile or young newly acquired Marine Betta will need live foods until they can adjust to captive life.  Tank-bred Marine Betta juveniles should be eating prepared foods and not be a problem.  They are hardy fish who are not aggressive, unless a crustacean or small fish can fit into it’s mouth.  Arrange the rock work to form ledges, since bright lights will make them hide more.  In a reef, this is particularly important since the bright lights for corals will keep your Marine Betta hidden.  They are much better off in a dimly lit aquarium.

Marine Betta can be harassed by more aggressive fish like triggers, damsels, large hawkfish, etc., so these fish should be avoided as tank mates.  Very aggressive feeding fish  and large fast swimmers will not only make it hard for the Marine Betta to get enough food, but will keep it from coming out.  They will come out when housed with more peaceful fish.  A resident Coral Shrimp usually is not bothered, but any other shrimp added after the Marine Betta will become lunch.  Two Marine Betta will get along in the same tank if they are male and female (they wont fight) and are added at the same time.  If is not a male and female, then the tank should be at least 6’ long.  

The minimum tank size for a single Marine Betta is 55 gallons (208 liters) with rock work arranged to form ledges and caves.  Wild-caught specimens will need live foods like live mysis if very small or newborn mollies and small feeder shrimp.  They can be trained to start eating prepared foods eventually.  Quarantining them will help get them acclimated to prepared foods.  They like calmer water, so pointing your pumps away from their preferred spot is appreciated.  Bright lights are too much for them and they will stay hidden, unless there are dark areas of the tank with over hangs and little light.  They swim at all levels of the tank, but prefer mid to lower levels.

Scientific Classification


Marine Betta – Quick Aquarium Care

Aquarist Experience Level:Beginner
Aquarium Hardiness: Very Hardy
Minimum Tank Size:55 gal (208 L)
Size of fish – inches: 8.0 inches (20.32 cm)
Temperature: 72.0 to 82.0° F (22.2 to 27.8&deg C)
Range ph:8.0-8.4
Diet Type:Carnivore
marine betta
Image Credit: JaysonPhotography, Shutterstock

Habitat: Distribution / Background

The Marine Betta, Calloplesiops altivelis was first described by Steindachner in 1903.  The common names they are known by are Comet, Marine Betta and Sea Betta.  Comet may refer to the black false eye spot among the “white stars” or spots on the body.  Betta refers to the well known freshwater Siamese Fighting Fish or Betta pose, (NOT pronounced Bay-ta, but pronounced Bet-ah) where all fins are exaggerated which gives them a much larger appearance than they are.

Distribution – Habitat:

The Marine Betta is found in the Indo-Pacific, in the Red Sea, then from East Africa to the Line Islands.  They are also found at the southern tip of Japan then south to the Great Barrier Reef and Tonga.  They are found on lagoon patch reefs, pinnacle reefs, reef faces and fore-reef slops hiding in caves and crevices along drop-offs.  They hunt at night, but hide by day under ledges and holes that they sometimes share with shrimp (stenopus hispidus), Spotfin Lionfish (Pterois antennata) and pygmy angelfish.  Marine Betta are found at depths from 10 to 148 feet (3 to 45 m) hunting crustaceans and small fish that are bite sized.

They are found alone, in pairs or in small groups as adults and in groups as juveniles.  A male Marine Betta that is protecting it’s egg clutch will position himself between the intruder and the eggs and will extend his dorsal fin to hide the eggs from view.  This behavior is the opposite of the normally reclusive fish that hides when there is any perceived danger.  The Marine Betta is not on the IUCN Red List for endangered species. 

  • Scientific Name: Calloplesiops altivelis
  • Social Grouping: Varies – Can be kept singly, in male/female pairs or an unknown pair if the tank is over 100 gallons.
  • IUCN Red List: NE – Not Evaluated or not listed


The adult Marine Betta is brownish black with tons of small white spots that form rows on the body.  Their eyes are completely concealed with white spots on the iris too! There is a black spot, or false eye the same size as their eye at the back of the dorsal fin, over the base of the tail fin area, which is used to deter predators or to confuse prey.  This spot is ringed in pale blue with the bottom of the ring being yellow.  The white spots that are closer the dorsal and anal fin, are pale blue and then after a few more rows, they seem to join and form pale blue vertical lines with the outer edges of of those fins, having thin bright blue and orange edging.  Their pectoral fins are quite cool, being clear, except for the rays or spines, which are bright yellow.  

New fry are blackish brown, then within 16 days the juveniles form a large white area on each side of their body, which shrinks in size as the fish grows.  A small juvenile that has lost his white center has two false eye spots, one above the base of the tail on the dorsal fin and one under the base of the tail on the anal fin.  The spots are larger on the body with several larger bright blue dots on the dorsal fin and on the anal and pelvic fins.  The Marine Betta typically grows to only 7” in captivity but in the wild grows to 7.8” (20 cm).  They are said to live 10 years or more in captivity.

  • Size of fish – inches: 8.0 inches (20.32 cm) – 7.8” (20 cm)
 – Most reach only 7” in captivity.

  • Lifespan: 10 years – Marine Betta can live 10 years or more with proper care.

Fish Keeping Difficulty

The Marine Betta is only challenging if it is wild caught, since it will only eat live foods.  Figure out where it is hiding and direct the live foods to their hideout.  Eventually, you can wean them onto prepared foods by putting the food in the pump stream, thus fooling them into chasing the food.  An established tank with lots of live rock swarming with natural foods will also help them adjust because they can get food right away.   Once they are eating prepared foods, they are a very hardy fish!  They are actually peaceful, only becoming a threat to very small fish and crustaceans.  More aggressive fish can harm them, so be wary of aggressive tank mates like larger dottybacks, large hawkfish and triggers.  

  • Aquarium Hardiness: Very Hardy
  • Aquarist Experience Level: Beginner – Once they are adjusted to prepared foods.
marine betta fish
Image Credit: Roberto Dani, Shutterstock

Foods and Feeding

The Marine Betta is a carnivore.  In the wild they will eat any small fish or crustaceans that will fit into their mouths.  When first captured they need gut loaded feeder shrimp, mysis or gut loaded mysis shrimp.  Once they are acclimated to prepared foods, they will accept frozen mysis shrimp, fortified brine shrimp, minced shrimp, scallops or ocean fish.  A few individuals, especially tank bred fish may accept flake or pellet, but this should not be the main diet.   Feed several times a day.

  • Diet Type: Carnivore
  • Flake Food: Occasionally – Flake for carnivores.
  • Tablet / Pellet: Occasionally – Sinking pellets for carnivores.
  • Live foods (fishes, shrimps, worms): Some of Diet – Newborn or appropriately sized mollies as a treat or live brine or mysis to get them to elicit a feeding response if wild caught. This can also be done to condition them for spawning if you have a male and female pair.
  • Meaty Food: All of Diet
  • Feeding Frequency: Several feedings per day

Aquarium Care

Reef tanks

  • Medium sized up to 90 gallons, perform 15% bi-weekly. 
  • Large Tanks 100 gallons and over, once water is aged and stable can be changed 10% bi-weekly to 20% monthly, depending on bioload.

Fish only tanks:

  • Medium sized up to 90 gallons, perform 20% to 30% monthly depending on bioload. 
  • Large Tanks 100 gallons and over, once water is aged and stable can be changed 20% to 30% every 6 weeks depending on bioload.

For more information on maintaining a saltwater aquarium see: Saltwater Aquarium Basics: Maintenance. A reef tank will require specialized filtration and lighting equipment. Regular water changes done  bi-weekly will help replace the trace elements that the fish and corals use up. Learn more about reef keeping see: Mini Reef Aquarium Basics.

  • Water Changes: Bi-weekly

Aquarium Setup

Minimum tank size is 55 gallons (208 liters) unless you want more than one comet, then the tank should be 100 gallons.  Form rocks to make ledges to help shield them from the lights.   Mature live rock helps to provide live food which will help your new wild caught Marine Betta to adjust.  Tank bred specimens will still benefit from mature rock. They are not picky about substrate, but bright lights will cause them to hide and not come out during the day at all.  They are happy with a steady temperature, somewhere between 72 and 81˚F (22 to 27˚C), a pH of 8.0 to 8.4 pH and normal seawater salinity of 1.023 to 1.025.  They are not particular about water movement, but a power head shouldn’t be pointed in the area they like to hang out under.  They will inhabit all areas of the tank, though mid to lower areas will be preferred if the light is very bright. 

  • Minimum Tank Size: 55 gal (208 L) – 55 gallons (208 liters)
  • Suitable for Nano Tank: No
  • Live Rock Requirement: Typical Plus Hiding Places – Form ledges and overhangs out of the live rock.
  • Substrate Type: Any
  • Lighting Needs: Low – subdued lighting
  • Temperature: 72.0 to 82.0° F (22.2 to 27.8&deg C) – 72˚ F (22˚ C) 81˚ F (27˚ C)
  • Breeding Temperature: 79.0° F – 79˚ F (26˚ C)
  • Specific gravity: 1.023-1.025 SG
  • Range ph: 8.0-8.4
  • Brackish: No
  • Water Movement: Any – Do not point powerhead near the area the fish likes to chill.
  • Water Region: Bottom

Social Behaviors

Marine Betta will fight if both are males.  If you are not sure what you have, put them in a tank that is at least 6 feet long.  A male/female pair should be okay in a 75 gallon tank.  As far as male and females, there is no way to tell what you have in that regard though it is thought males are larger.  They are a peaceful fish that gets along with most tank mates as long as they don’t fit in their mouths.  

They should not be housed with small fish like clown gobies, or any fish that are thin or skinny like small juvenile flasher wrasses for example.   They do well with Fairy Wrasses, larger Flasher Wrasses, anthias, clownfish, less aggressive dwarf angelfish, jawfish, large gobies and blennies, cardinals and smaller hawkfish.  The Marine Betta should be added when very young and when these other fish are full grown. This should imprint on their minds that the tank mates are friends, not food!  Keep your Marine Betta well fed.  Do not house with aggressive fish, since the Betta will be most likely picked on.  Such fish would be aggressive large dottybacks, large hawkfish, damsels, and triggers.  Large predatorial fish like groupers and lionfish will eventually become large enough to eat your Marine Betta!  Fast moving fish will keep your Betta from coming out such as tangs, large angelfish, larger wrasses, triggerfish, etc.

Corals are perfectly safe with this beautiful fish, but your Marine Betta will not appreciate the bright lighting and will hide most of the time in a full reef tank.  If you want corals, maybe only put corals only in the middle, leaving the outer corners dark for the Marine Betta.

Marine Betta will eat crustaceans, especially shrimp.  A shrimp that was present when the Marine Betta juvenile is added, such as a coral shrimp, should be left alone.  Add a Peppermint Shrimp in AFTER the Betta is settled, and they will be taken down one by one!  They may not bother cryptic starfish like brittle stars.  Many people report them not bothering larger snails.

  • Venomous: No
  • Temperament: Peaceful – Only aggressive to bite sized small fish or shrimp.
  • Compatible with:
    • Same species – conspecifics: Sometimes – Male and female will get along but two males will fight and need 100 gallons or more.
    • Peaceful fish (gobies, dartfish, assessors, fairy wrasses): Safe – No small clown gobies.
    • Semi-Aggressive (anthias, clownfish, dwarf angels): Safe – No juvenile clownfish that can fit in their mouth.
    • Monitor – These fish may be too aggressive for the Marine Betta
    • Large Semi-Aggressive (tangs, large angels, large wrasses): Monitor – Large fast moving fish like large wrasses, large angelfish, butterflyfish and tangs may intimidate the Marine Betta from coming out.
    • Large Aggressive, Predatory (lionfish, groupers, soapfish): Threat
    • Monitor – Mandarins are as slow and methodical eaters as the Marine Betta and will be left alone.

    • Anemones: Safe
    • Mushroom Anemones – Corallimorphs: Safe
    • LPS corals: Safe
    • SPS corals: Safe
    • Gorgonians, Sea Fans: Safe
    • Leather Corals: Safe
    • Soft Corals (xenias, tree corals): Safe
    • Star Polyps, Organ Pipe Coral: Safe
    • Zoanthids – Button Polyps, Sea Mats: Safe
    • Sponges, Tunicates: Safe
    • Shrimps, Crabs, Snails: Monitor – Resident Coral Shrimp are safe, but adding other shrimp like Peppermint Shrimp after the Marine Betta will be eaten. Some state large crabs and snails that were in the tank first are not bothered.
    • Starfish: Safe
    • Feather Dusters, Bristle Worms, Flatworms: Safe
    • Clams, Scallops, Oysters: Safe
    • Copepods, Amphipods, Mini Brittle Stars: Safe

Sexual differences

Males are larger than females.

Breeding / Reproduction

Not much is known about how they reproduce in the wild.  So far, what is known about the eggs and young is interesting!  The eggs have an adhesive string like substance that connects them all and keeps them stuck to the underside of the cave or ledge.  The eggs are golden brown and number from 300 to 500, and are only 1 mm in diameter.  The male will stop eating and will guard the eggs while fanning them to keep them free of debris.  The eggs hatch in five or six days at 79˚F (26˚C) and the fry are 0.12 to 0.16” (3 to 4 mm) long.  The fry are well developed and start to feed immediately.  In 14 days they are .24 to .32” (6 to 8 mm) long and at 16n days will develop a white spot on each side of their bodies, with the rest of the fish being dark.  As they grow, by 2 months, spots start to appear on their face, but they keep that white spot until they are 7 months old..  

The Marine Betta has been bred in captivity and has been available since December of 2012.

  • Ease of Breeding: Moderate

Fish Diseases

Marine Betta are probably the most bulletproof marine fish out there!  They don’t seem to suffer from Crypt, even when all the other fish have it.  If it gets cut or scraped it heals up without infection and bacterial infections are very rare as well.


These fish are found on the internet and can be pricy.


  • BOOKS:
    By Scott W. Michael
    Published by T.F.H. Publications
    Co-Published by Microcosm Ltd.
    Copyright © 2004 by T.F.H. Publications, Inc.
    Photographs copyright © Joshua Highter
    2006 Annual Volume 8
    SPECIES PROFILE Marine Betta – Calloplesiops altivelis
    Page 102 & 103
    REEFKEEPING – An online magazine for the marine aquarist
    Brought to you by Reef Central
    Fish Tales
    By Henry C. Schultz III
    Bet You’ll Love These Bettas
  • Reefkeeping Magazine™ Reef Central, LLC-Copyright © 2008 All rights reserved
    Aquarium Fish Information
    Marine Betta (Calloplesiops altivelis)
    © Fish
    Sustainable Aquaitic captive-bred Marine Bettas trickling out to fish stores now
    By Jake Adams
    ©2006-2014 Reef Builders. Reef Builders®, and the Reef Builders® logo are registered trademarks of Reef Builders, Inc. ALL RIGHTS RESERVED.
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Featured Image Credit: Marine Comet (Calloplesiops altivelis) (Image Credit: George Berninger Jr., Wikimedia Commons CC BY-SA 3.0 Unported)