An often overlooked and sometimes not even seen family of marine fish is regularly referred to as "roundheads." These gentle and shy fish can make wonderful additions to a reef tank if the hobbyist follows a few simple steps. All too often these fish get overlooked at the local fish store. This isn't because the hobbyists find them boring or unattractive, but rather they simply do not see these fish in the tanks of the retailers. After reading and learning about this small family, it's likely that many of you will begin to search for them from now on.

The family Plesiopidae, sometimes called "roundheads" or "longfins," contains two subfamilies, eleven genera, and 38 species. Plesiopinae, one of the subfamilies, has seven genera and 26 species. The seven genera are Assessor, Calloplesiops, Fraudella, Paraplesiops, Plesiops, Steeneichthys, and Trachinops. Within these seven genera are 26 species. Acanthoclininae is the second subfamily and contains the remaining four genera: Acanthoplesiops, Acanthoclinus, Belonepterygion, and Beliops. Twelve species can be found within these genera.

Plesiopidae can be found throughout the Indo-West Pacific. They lack scales on their head and gill plates. They have an incomplete or separated lateral line and pectoral fins comprised of one spine and either two or four soft rays. Their third branchiostegal ray extends farther to the rear than adjacent rays and results in a projection on the margin of the branchiostegal membrane (except in Calloplesiops) (Fish Base).

For the rest of this article I'm going to focus on one genus, Calloplesiops. At the end I will touch on the other genus that shows up regularly in our hobby, Assessor. The care of these two genera is very similar. One can assume the captive care requirements for Assessor is identical to that of Calloplesiops, except where differences are noted.

Calloplesiops contains only one species, C. altivelis. In years past two species were recognized: C. altivelis and C. argus. It was believed the only difference was in the size, shape, and number of spots. Further investigation revealed the difference was only in the age of the animal and two separate species did not exist. C. argus was the older color phase of C. altivelis. The older color phase has a large white spot on the end of the tail, with smaller more numerous spots, and stripes on the median fins. It has since been revised such that C. argus is no longer a valid species (Coral Realm).

C. altivelis, also known as a marine betta or Comet, can be found throughout recreational scuba depths, 10 - 150 feet (Debelius et al, 1994). They remain tucked tightly into crevices and hanging underneath caves during daylight hours. Rarely will they venture into direct light. Comets will become active only during night hours. "Active" is a relative term, however, as some may never venture outside of their cave by more than a meter. As nightfall approaches, they begin feeding. Their prey consists mostly of small crustaceans and small fish. They are slow feeders, often giving their prey a long stare prior to the attack. The attack is predictable; the Comet will hover slightly above it's prey with it's head lower than it's tail. All of its fins are fully opened, its pectoral fins are fluttering, and the tail is curled. Using it's pectoral fins, it makes a quick stab at the prey. Rarely does it miss. It will carry this trait into the home aquarium, though I've witnessed this natural instinct fade as the years progressed. I surmise it was the unnatural food that caused the natural "killer" instinct to diminish. The University of Texas at Austin has an excellent video clip of this feeding posture. To view the clip click here. It takes one or two minutes to download on my cable modem, so give it a few minutes after you click their link.

The Comet has two natural defenses. The first obvious defense is the false eyespot that is displayed near the rear of the fish. The real eye is virtually impossible to see. There are many other marine fish that employ this same defense. A common place for aggressive fish to attack is the eye. By having a false eyespot on the rear of the fish the aggression is averted away from the fish's real eye. The second defense, known as Batesian mimicry, is instinctive behavior that can occasionally be viewed in our tanks. The Comet will dive head first into cover at the first sight of danger. Rather than bury itself and completely hide, the fish will leave his back end viewable. To the potential attacker this looks similar to a Gymnothorax meleagris, the white-mouth moray eel, and usually results in the attacker withdrawing (Lieske, 1999). This defensive posterior can be viewed in the last three seconds of the above linked video clip.

Prior to purchase ensure you have the proper environment for your Comet. The tank should have numerous crevices which are devoid of light. A cave or an overhang is highly recommended. Brightly lit tanks are not the best option, but as long as dark corners exist your Comet will be fine.

Getting a Comet acclimated to your tank conditions will be the biggest hurdle you'll have to overcome. They acclimate slowly to the aquarium. Once added, they will generally dive deep into your rockwork for up to a week or more. If you want to see your Comet more often during daylight hours, setup a cave or overhang that is devoid of direct light. Choose one corner or the other, not the center of the tank. This should avoid a good percentage of traffic from swimming fish. Avoid any direct light. Light reflected from the sandbed should also be avoided. However, make sure this cave is readily viewable, as you will initially need to sneak up to the tank to observe your Comet. Actinic lights are another great addition for additional viewing of the Comet. With a dawn/dusk photoperiod you'll get to witness the Comet in open water on a timed schedule. They tend to appreciate the softer light that actinics provide, and reward you with extended viewing of your fish.

Getting your new Comet to accept prepared foods is another tricky part of successfully maintaining this fish. I suggest trying prepared foods first, not live foods. It's probably best that your Comet not become accustomed to live foods unless it becomes necessary to induce a feeding response. Since Comets are night predators, night feeding might be necessary. Feeding during your tank's actinic phase is perfect. Try frozen/thawed mysis or plankton as your first offering. Most fish find this food irresistible. Small frozen/thawed krill or silversides would be another choice, followed by brine shrimp. It may take your Comet a week or more before it takes it's first food. I wouldn't concern myself until two weeks have passed with no feeding observed. Comets have a rather slow metabolism. After two weeks without a confirmed meal, I'd switch to live foods to entice feeding. Live freshwater mollies, ghost or grass shrimp, black worms, or brine shrimp should be fed. I suppose live peppermint shrimp could work as well. Eventually, you'd like to get the Comet weaned towards prepared foods. Long-term diets should include mysis, plankton, Formula 1™, krill, and silversides.

Consideration of tank mates is important in the Comet tank. Large, fast swimming fish should be avoided if you wish to see the Comet during daylight hours. They should be avoided completely prior to introduction and acclimation of your Comet. This would include, but is not limited to, surgeonfish, large angels, butterflies, and some wrasses. These larger, active swimmers will keep your Comet deep in the rockwork until the lights go off. Active feeders are also a bad idea since they will out compete the Comet for food.

Since Comets will consume small fish it is recommended to not add small fish, unless intended as a meal. Don't think their natural instinct has changed, it hasn't. Speaking from experience, this instinct will never fade. I successfully kept a mated pair of Coral Banded Shrimp (Stenopus hispidus) for years with my Comet. Thinking it was safe, I introduced five Peppermint Shrimp (Lysmata wurdemanni) hoping to clear out my Aiptasia. The shrimp cost me $45, but what I paid for was one last view of the Comet's "killer" instinct. Immediately the Comet came out of the rockwork and consumed two of them. The remaining three were missing by the weekend. I was never daring enough to mix small gobies or other small fish, but an educated guess says it is not a wise idea.

Shrimp like this Stenopus hispidus can co-exist with a Comet.	Lysmata wurdemanni should be avoided unless intended as a meal.

Good tank mates for a Comet would include small wrasses, dwarf angels, grammas, jawfish, larger gobies and blennies, cardinals, and hawkfish, to name a few. For the most part, the Comet will leave its tank mates alone. However, on occasion it may need to defend it's favorite cave. These are non-violent attacks, causing no damage to the intruder. A juvenile Comet can live in a 20 or 40 gallon tank comfortably, while the adult may require the added length of a 55 gallon. Depending on tank mates, a larger tank might be necessary. The size of an adult Comet may require a 6' tank when keeping two adults of the opposite sex together.

Compatibility chart for Calloplesiops altivelis:

Fish	Will Co-Exist	May Co-Exist	Will Not Co-Exist	Notes
Angels, Dwarf	X			Ensure your Comet receives enough food
Angels, Large		X		Often too active of a swimmer and feeder
Anthias	X			Excellent choice
Assessors		X		Keep only with juvenile Comets. Adult Comets can consume adult Assessors
Basses		X		Some basses are very aggressive towards tank mates
Batfish			X	Aggressive feeding and swimming habits
Blennies	X			Excellent choice
Boxfishes		X		Often too active of feeders
Butterflies		X		Often too active of a swimmer and feeder
Cardinals	X			Excellent choice
Catfish		X		As the catfish grow they become more of a threat towards Comets
Comet		X		Opposite sex individuals can be kept as a pair
Cowfish	X			Excellent choice
Damsels		X		Some damsels may be overly aggressive towards tank mates
Dottybacks		X		Most dottybacks are too aggressive towards tank mates for Comets; should do fine with P. springeri and P. fridmani
Dragonets	X			Excellent choice
Drums	X			Excellent choice
Eels		X		Some eels are too aggressive for Comets
Filefish	X			Excellent choice
Frogfish		X		Frogfish will consume fish equal to their own length
Goatfish		X		Some goatfishes get large enough to consume small Comets
Gobies		X		Comets may consume smaller gobies
Grammas	X			Excellent choice
Groupers			X	Aggressive feeding and swimming habits; smaller Comets may be consumed by larger groupers
Hamlets	X			Excellent choice
Hawkfish	X			Excellent choice
Jawfish	X			Excellent choice
Lionfish		X		Excellent choice with adult Comets; juveniles may be eaten by larger lionfish
Parrotfish			X	Aggressive swimming habits
Pineapple Fish	X			Excellent choice
Pipefish		X		Comets may consume smaller Pipefish
Puffers			X	Aggressive feeding and swimming habits
Rabbitfish		X		Often too active of a swimmer and feeder
Sand Perches	X			Excellent choice
Scorpionfish		X		Scorpionfish may consume smaller Comets
Seahorses		X		Adult Comets will consume smaller ‘horses
Snappers		X		Will consume smaller Comets
Soapfishes		X		May attack and consume smaller Comets
Soldierfish		X		Large adult Soldierfish can consume small Comets
Spinecheeks	X			Excellent choice
Squirrelfish		X		Large adult Squirrelfish can consume small Comets
Surgeonfish		X		Often too active of a swimmer and feeder
Sweetlips	X			Excellent choice
Tilefish	X			Excellent choice
Toadfish		X		Toadfish will consume anything that can fit in their mouth
Triggerfish			X	Aggressive feeding and swimming habits
Waspfish	X			Excellent choice
Wrasses		X		Often too active of a swimmer and feeder

Note: While many of the fish listed are good tank mates for Calloplesiops altivelis, you should research each fish individually before adding it to your aquarium. Some of the mentioned fish are better left in the ocean or for advanced aquarists.

Captive Reproduction

Captive reproduction of C. altivelis is possible in the home aquarium. It is not easy to breed and raise this species, but hobbyists with prior experience in raising saltwater fry should be capable of succeeding.

Sexing Comets is next to impossible since there is no sexual dichromatism. The only known method of determining sex is by observation: two males will fight and a male and female will not fight, provided adequate room is available in the tank.

The female Comet lays a single egg mass of roughly 500 eggs. Adhesive strands connect and attach all the eggs to the wall of the cave. In roughly 5 - 6 days, the eggs hatch during the evening into well-developed fry. They are roughly 3mm long and already possess their typically large pectoral fins, mouth, and eyes. Within two weeks, the fry begin losing their black pigment, turn white, and take-on the adult-like reclusive nature. Adult coloration is finally reached around seven months of age or 3cm of length, though a strong resemblance to final adult coloration is usually present around eight weeks. (Debelius et al, 1994). If you are interested in good photos of the various stages of fry development, return to the University of Texas at Austin or Living Reef Images websites.

Assessors, sometimes called "devilfish," appear in the trade less than Calloplesiops altivelis. This is unfortunate, as they are wonderfully colored and great additions to peaceful aquariums with small fish. Three species have earned the title Assessor: A. flavissimus, A. macneilli, and A. randalli. The latter rarely shows up in the hobby, probably because of its drab coloration. They barely reach two inches in length and are found in shallower water than the Comet. They still avoid bright daylight, but have a tendency to be slightly more outgoing in the passive aquarium. A 20 gallon aquarium will be large enough to house one adult Assessor.

Devilfish can do well kept as a single individual or in larger tanks as pairs. Two males will fight, however, making our job somewhat harder. To compound this problem, they are not sexually dichromatic.

Much like the Banggai Cardinalfish (Pterapogon kauderni), the male Assessor will mouth brood the young until they hatch, usually around the fourteenth day. Captive breeding in home aquariums has been reported.

Pterapogon kauderni makes an excellent tank mate for Calloplesiops altivelis.

Calloplesiops altivelis aha Comet or Maine Betta, has a range of from the Red Sea, Japan, the Philippines, and the Great Barrier Reef. They live singly within their crevices and caves. A full grown adult can reach 8" long. Once acclimated and established in your tank they are extremely disease resistant and can live for well over a decade. Avoid small fish and invertebrates that can fit into it's mouth. They will not bother corals. Rather than allow words to do an inadequate job of describing them, I'll simply allow you to view one in all their magnificent glory.

Calloplesiops altivelis

Assessor flavissimus, more commonly called the yellow assessor or golden devilfish, will do best housed by itself, though pairs are possible. Small fish or shrimp are not threatened by this "devilfish." Their brilliant yellow coloration will quickly grab your attention. You can find these in East Australia, usually less than 60 feet deep.

Assessor flavissimus

Assessor macneilli, also called the MacNeill's mini-grouper, is a stunning deep blue or purple, almost black. They can be found in the South Pacific and the Great Barrier Reef, sometimes in groups of up to 100 individuals. This allows larger harems to be kept in the home aquarium.

Compatibility chart for Assessor sp.:

Fish	Will Co-Exist	May Co-Exist	Will Not Co-Exist	Notes
Angels, Dwarf		X		Depends on individual Angel; most will be too aggressive
Angels, Large			X	Too large and aggressive; you’ll never see your Assessor
Anthias	X			Excellent choice
Assessors		X		Some species can be kept in pairs or harems
Basses		X		Most adult basses can consume Assessors
Batfish			X	Too large, aggressive feeding and swimming
Blennies	X			Excellent choice
Boxfishes		X		Boxfishes shouldn't attack Assessors, but their overall size may keep the Assessor hiding
Butterflies		X		Aggressive swimmers and feeders
Cardinals			X	Adults can consume Assessors
Catfish			X	Adults can consume Assessors
Comet		X		Large adults can consume Assessors
Cowfish		X		Cowfish won't attack Assessors, but their overall size may keep the Assessor hiding
Damsels			X	Overly aggressive for an Assessor tank
Dottybacks			X	Overly aggressive for an Assessor tank; will hunt down Assessors
Dragonets	X			Excellent choice
Drums	X			Excellent choice
Eels			X	Will consume Assessors
Filefish	X			Excellent choice
Frogfish			X	Will consume Assessors
Goatfish			X	Larger adults will consume Assessors
Gobies	X			Excellent choice
Grammas		X		Grammas can become territorial in smaller tanks
Groupers			X	Will consume Assessors
Hamlets	X			Excellent choice
Hawkfish	X			Excellent choice
Jawfish	X			Excellent choice
Lionfish			X	Will consume Assessors
Parrotfish			X	Aggressive swimmer
Pineapple Fish	X			Excellent choice
Pipefish	X			Excellent choice
Puffers			X	Will consume Assessors if it can catch them; aggressive feeder
Rabbitfish		X		Aggressive swimmers and feeders
Sand Perches		X		Larger adults may aggressively attack Assessors
Scorpionfish			X	Will consume Assessors
Seahorses	X			Excellent choice
Snappers			X	Adults can consume Assessors
Soapfishes			X	Adults can consume Assessors
Soldierfish			X	Adults can consume Assessors
Spinecheeks		X		Adult size can be intimidating
Squirrelfish			X	Adults can consume Assessors
Surgeonfish		X		Aggressive swimmers and feeders
Sweetlips		X		Adult size can be intimidating
Tilefish	X			Excellent choice
Toadfish			X	Will consume Assessors
Triggerfish			X	Aggressive swimmers and feeders; may consume Assessors
Waspfish			X	Will consume Assessors
Wrasses		X		Aggressive swimmers and feeders

Note: While many of the fish listed are good tank mates for Assessor sp., you should research each fish individually before adding it to your aquarium. Some of the mentioned fish are better left in the ocean or for advanced aquarists.

Nemateleotris decora, a great tank mate for Assessor sp.

In Conclusion

The three species presented here make wonderful additions to most reef tanks. Hopefully, you will not overlook these attractive species the next time you come across one.

Baensch, H.A., 1994. Roundheads. Pp. 994 - 1011. Baensch Marine Atlas, Volume 1. Microcosm. Shelburne. 1215 pp.

Burgess, W.E., et al, 1991. pp. 209 - 212. Dr. Burgess's Mini-Atlas of Marine Aquarium Fishes Mini-Edition. T.F.H. Publications. Neptune city. 1023 pp.

Lieske, E. and Myers, R., 1996. pp. 19, 30. Coral Reef Fishes. Princeton University Press. Princeton. 400 pp.

Michael, S. W., 1999. Assessor/Comet. pp.128 - 130. Marine Fishes: 500 + Essential-To-Know Aquarium Species. Microcosm. Shelburne. 447 pp.

Michael, S. W., 1998. Family Plesiopidae. pp. 102 - 103. Reef Fishes Volume 1. Microcosm. Shelburne. 624 pp.

On the Web

Australian Museum Fish Site

Living Reef Images

University of Texas at Austin

Fish Base

Coral Realm

Photo Credits:

Calloplesiops altivelis: Greg Rothschild
Assessor flavissimus: Leslie Leddo
Pterapogon kauderni: Greg Rothschild
Stenopus hispidus: Greg Rothschild
Lysmata wurdemanni: Greg Rothschild
Nemateleotris decora: Greg Rothschild