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Related FAQs: Marine Bettas, Roundheads,

Related Articles:  Roundheads

/The Conscientious Marine Aquarist

The Roundhead Called the Marine Betta, Calloplesiops altivelis, Family Plesiopsidae

by Bob Fenner

Aquarist pic of the Marine Betta

A quiet beauty, the Marine Betta, aka Comet is a real looker, though shy, retiring to the point of being reclusive in its initial behavior. With time, patience, this silent stalker can be enticed to be a bit more outgoing. Providing sufficient space, hiding places, a dearth of busy fish tankmates... and possibly live foods to begin with, are about all that are required to keep Calloplesiops altivelis.


    The Roundhead family (Plesiopsidae) is quite "bass-like" in its appearance, was at one time included with them and is closely allied with Serranid fishes. Though slow moving comparatively, these groups share a similar hunting and feeding strategy.

Calloplesiops altivelis Steindachner 1903, the Comet or Marine Betta. Indo-Pacific, including the Red Sea to Tonga and the Line Islands. To a bit over six inches. A shy species that requires a dark cave and peaceful tankmates to thrive.  http://fishbase.org/Summary/SpeciesSummary.php?id=12655

    All told there are some 38 described species of Roundheads, divided in 11 genera: http://fishbase.org/Summary/FamilySummary.cfm?ID=294. With the exception of the Marine Betta and a couple of members of the genus Assessor, other Plesiopsids are rare in our interest.

Other Family Plesiopsidae Members You May Find For Aquariums:

Assessor flavissimus Allen & Kuiter 1976, the Yellow Devilfish. Great Barrier Reef (Australia) endemic. To a little over two inches in length. 

Assessor macneilli Whitley 1935, the Blue Devilfish. Found on Australia's GBR and New Caledonia. To two and a quarter inches in length. One photographed off Heron Island, Qld, another in an aquarium.

Bigger PIX:
The images in this table are linked to large (desktop size) copies. Click on "framed" images to go to the larger size.

Paraplesiops poweri Ogilby 1908. Southwest Pacific. Occasionally imported out of Australia. To six inches in length. This too-thin one at a Los Angeles wholesaler. 


    Plesiopsids are in a word, shy... Once accustomed to their settings, and absence other fast-moving, aggressive fish tankmates, yours may well come out more frequently, even learn to eat from your hand... But in the wild, and when new to captivity these fishes are generally out of sight... hiding under caves, under nooks... venturing out only when darkness is coming on to feed.

Oh, is the Marine Betta a Batesian mimic of the Moray Eel, Gymnothorax meleagris? Some would-be predators evidently think the head of the moray and the tail of the Comet are similar... In the wild, if frightened, Comets turn around showing their rear dorsal "ocellus" (false eye-spot)... looking like the Guineafowl Moray.


    The Marine Betta gets along with all easy-going slow/er moving livestock... with the exception of  fishes and shrimp tankmates small enough to fit in its mouth. The larger the system the better your chances for overall compatibility... With more nooks and crannies to hide in being ideal.


    Calloplesiops generally ship well (being kept in the dark helps I'm sure), and are by and large good at adapting to captive conditions. Look for a specimen that has been at your dealers at least a few days (most "anomalous losses" occur within this time), and is at least settled in well-enough to show interest in food, if not feeding in your presence. Be wary of specimens with any apparent damage to their mouths, or bloody marks on the body or fin spine origins. Split fins themselves are not typically problematical, healing in a week or two.

    Be wary of very thin specimens... Like all marines, these fish are not fed for days to weeks while being held by collectors, shippers, most wholesalers... and of course in transit. This cumulative non-fed time can add up to so much stress that the animals may either "give up" on feeding or die outright from starvation. Avoid too-thin purchases.


    Though the Marine Betta is neither a large fish, nor one with a high metabolism, this species appreciates room to move about during its nightly forays. I would not place this fish in something with less than a four foot length, or a hundred gallons volume. 

    In the wild Calloplesiops is invariably encountered either "hanging" just inside an overhang or further into a cave like crevice during the day/light hours... venturing out a bit during the night to forage. Hiding spaces can be fashioned of live or base rock, with or w/o sedentary invertebrates perched about them. Bright lighting can be employed, but this will further limit the time your Betta will start to and stay out in the open during "lights on".


    Once trained, Calloplesiops will usually feed on most all bite-sized meaty items, cut/fresh or frozen/defrosted, or commercially made. On arrival from the wild though, often they need to be offered some small live food to "get them going"... Small shrimp, like "ghost" or grass (Palaemonetes sp.)  are ideal... soaked in a vitamin prep. like Selcon even better. Mixing these whole meaty foods with prepared, frozen/defrosted or home-made prep.s will slowly wean them off the live.


    Roundheads score high on the scale of pathogenic disease resistance. Like their bass kin, they are near the last to contract such protozoan diseases as Cryptocaryon. If they should need to be treated, they have a general tolerance of metal and dye medications.


    This species has been spawned in captivity and its young raised commercially (see the references below). All specimens offered for sale currently are wild-collected however. After spawning, the fertilized eggs take about 5 - 6 days to hatch. They hatch out at about 3 mm long. What would you feed these guys? Enriched brine shrimp, copepods of appropriate size... Pairs should be purchased as such, rather than trying to match them up as singles... unless you have hundreds of gallons of room, and plenty of time...


    Contrary to appearances, Marine Bettas are not touchy or fussy in the ways of  foods and feeding. Due to their retiring behavior and small numbers that enter the trade, they don't get the attention they deserve. If you have "reef" conditions and room for a medium sized specimen, and no small shrimp, do consider a Calloplesiops. This quiet beauty will elicit oohs and aahs when it makes its occasional visits.

Bibliography/Further Reading:

Baez, Jacqueline. 1998. Breeding the Marine Comet: A challenge for the best. SeaScope v. 15, Summer 98.

Hunziker, Ray. 1987. Majestic marines: Calloplesiops altivelis and C. argus. TFH 12/87.

Lapira, Noel E. 1973. This is the Comet. TFH 1/73.

Michael, Scott W. 1991. A guide to the Comets (genus Calloplesiops). SeaScope v.8, Spring 91.

Michael, Scott W. 1996. Roundheads- dwellers of coral caverns. AFM 4/96.

Wassink, Herman. 1990. A successful cultivation of the Comet, Calloplesiops altivelis (Steindachner 1903). SeaScope v.7, Spring 90.

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