Fish Tales by Henry C. Schultz III

A Ring Around a Wrasse: The Genus Hologymnosus


It arrives as a small, little wrasse often very curious and aware of its tankmates and surroundings. "Surely it will do well," the hobbyist thinks, "it is cute and appears alert." What these fish eventually become, however, is anything but small and curious. Information about these "little guys" isn't easy to find. Of course, gathering information about them, as well as simply identifying them, is hindered by the presence of three different color varieties in each species. As a result, many local fish stores may not be able to offer accurate information regarding these wrasses' home aquarium care. As is often the case, the lack of quality information will result in an impulse purchase - one that would likely have been avoided if quality information had been readily available. And so, it is with a bit of hope that these fish will ultimately find their way into large aquariums featuring other large, carnivorous fish, that I'd like to present this article on the marine fish from the genus Hologymnosus, also called the "Ringed Wrasses."

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The juvenile Hologymnosus doliatus is possibly the most frequently encountered member of the genus in the aquarium trade. Unfortunately, the attractive looks of this fish usually result in a quick, uninformed purchase. Photo courtesy of John Randall.

Meet the Family

The family Labridae, the second largest marine fish family, consisting of more than 65 genera and 460 species, contains the genus Hologymnosus. Unlike many other fishes, the labrids use their pectoral fins extensively for swimming, while using their tail only on rare occasions, usually when escaping danger. Individuals in the genus Hologymnosus take their tail usage a step further and use it for lightning-quick speed which aids in their prey capture. Additionally, the tropical labrid species found in the reef aquarium trade are characterized by being protogynous hermaphrodites; most males are females that underwent a sex change.

Although often mistaken as a Coris species wrasse, Hologymnosus is distinctive enough to have been a recognized genus for over 200 years. At one time Valenciennes (1839), revised the genus and, described his "new" fish in a newly erected genus, Julis. Shortly thereafter, however, Bleeker (1862) recognized that Julis was an invalid synonym, and the genus reverted to its original name, Hologymnosus. With the name of the genus finally resolved, ichthyologists moved on to another conundrum - how many species are there? Today, I can sit here and affirmatively write that presently four recognized species exist. I can do so, however, only after the culmination of two centuries of research.

The first species named was Hologymnosus semidiscus. The remaining three species were awarded the names annulatus, fasciatus, and doliatus, respectively. However, when Valenciennes (1839) revised Hologymnosus to Julis, he also considered fasciatus and semidiscus as synonyms of annulatus, while continuing to recognize H. doliatus as a valid species. Thus, only two species were recognized at that time. Consequently, as the years passed collected specimens were regularly incorrectly documented. In most cases only a single specimen was recognized - H. semidiscus. Finally, Randall (1982) set the record straight when he revised the genus, resurrecting some of the synonymized forms and naming a total of three distinct species, while mentioning a possible fourth that required more research. In 1988 Randall and Yamakawa were sufficiently convinced to officially name this fourth and final (for now) species: H. rhodonotus.

Hologymnosus
annulatus
doliatus
longipes
rhodonotus

The alert reader may have noticed the absence of H. semidiscus and fasciatus from the above species list. Hologymnosus fasciatus was left as a synonym of annulatus by Randall (1982). Hologymnosus semidiscus, however, was the first name used for any Hologymnosus species, so it's natural to think this name should still be used today. When Valenciennes revised the genus and placed semidiscus as a synonym of annulatus, he was in fact the first author to revise the genus. Therefore, despite his incorrect research and conclusions, priority must be given to the first reviser. As such, semidiscus remains a synonym of annulatus.

So, what must a fish possess in order to be included into the elite club of Hologymnosus? Actually, the list is quite extensive (and probably boring to all but the most curious hobbyist). A few key elements are: 12 dorsal rays, 12 anal rays, 13 pectoral rays, and a fully continuous lateral line. Additionally, among the 14 - 21 small conical teeth per side of the jaw, there are two pairs of larger canine teeth up front. The largest teeth, however, are located on the first and second row (there are a total of six rows) of the upper pharyngeal bone.

It should also be noted that all Hologymnosus species lack the well-developed molariform teeth which are normally found on the pharyngeal bone of wrasses in the genera Coris, Halichoeres, Bodianus, Thalassoma, among others. These teeth are especially useful for feeding upon hard-shelled invertebrates.

In the Wild

All Hologymnosus species can be found in Indo-Pacific waters, but H. annulatus enjoys the largest geographical distribution within the genus (thus it is not surprising that it was also the first species described, as H. semidiscus). This species can be found from the Red Sea and east coast of Africa to French Polynesia, and from the Ryukyu Islands south to Australia. Other species, such as H. longipes, are much more geographically limited. Hologymnosus longipes is found only in the southwestern Pacific around Vanuatu, the Loyalty Islands, and New Caledonia. All species of the genus are found throughout variable depths ranging from 20 to nearly 100 feet.

As was mentioned earlier, all male Hologymnosus species are the result of a sex change. In the case of the Ring wrasses there are three distinctive color variations. Young individuals are known to have what is referred to as 'juvenile-phase' color form. When these juveniles age into adults they grow ovaries (and hence become female), change their colors and adapt the 'initial-phase' color form. Although not common among Labrids, Hologymnosus females are capable of becoming male while still maintaining the initial-phase color form. These individuals are referred to as 'primary-phase' males. When females, or those rare males, undergo their final transformation and color change they are said to have taken their 'terminal-phase' or 'terminal-male' color form. As the name implies, these individuals will remain males for the remainder of their life and will not change color again.

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The Candycane Wrasse, H. doliatus, wearing its intermediate coloration. At around 3 - 4 inches of length the juveniles will begin their transformation into this color form. Once they arrive at this stage, the aquarist would be wise to begin making plans for how the large adult will be maintained. Photo courtesy of John Randall.

Ring wrasses can grow rather large. Individuals of over one foot in length are not considered uncommon. But before they are large, they have to begin as small juveniles, and in the case of Hologymnosus, they settle from pelagic life at roughly 24 mm (0.9 inches) in length. As juveniles, they congregate in small harems over open sand and rubble areas adjacent to reefs. Females will typically abandon their harem and begin to associate with goatfish, snappers, and other fish that disturb the sand in search of food. In contrast, males are usually found roaming great distances by themselves, regularly checking on the females within their territory and defending territory from other males.

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A preserved adult male specimen of Hologymnosus annulatus is seen here sporting the terminal phase coloration. Once these fish reach this size, realistically they may not be able to be housed in any but the largest home aquariums. Even still, selection of tankmates will have to be well thought out to ensure they do not become a meal for this fish. Photo courtesy of John Randall.

Juveniles will hunt for the typical wrasse foods consisting of a plethora of hard-shelled crustaceans and microfauna. The females are more voracious, hunting larger shrimps and crabs, while adult males that reach over 12" have a rather large appetite and to help meet their insatiable demand for food, this fish will consume most any mobile animal it can capture and swallow. In the case of Hologymnosus annulatus this means over 88% of their diet consists of fish, with roughly 6% consisting of shrimp and 4% of crabs and unidentifiable crustaceans. In contrast, the diet of H. doliatus was significantly different with only 40% of its diet consisting of fish, while 17% was crabs, 13% shrimp, 2% starfish, and the remaining 22% made up of unidentifiable crustaceans. Of particular interest to astute aquarists is the fact that over 3% of its diet consists of mantis shrimps (Randall, 1982).

The Ringed wrasses use the sandbed not only as a place to sleep, but for defense as well. Like all wrasses, Hologymnosus are diurnal. Every night when the wrasse retires for the evening, or when they feel threatened by another predator, they quickly dive into the sandbed, leaving no tell-tale signs except for a small cloud of sand dust, which quickly dissipates. It is there that they sleep until the sun rises again, or lie in wait until the threat has left the area, at which time they slowly rise out of the sandbed and inspect their surroundings before fully emerging. Sand sometimes sticks to their slime coat for a few minutes after rising from the sand, but is usually blown off by the currents in short order.

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The beauty of the intermediate color phase female Hologymnosus rhodonotus can certainly hold its own against most Cirrhilabrus species wrasses, but they do not mix into an aquarium as well as Cirrhilabrus. Regardless, even though these fish have been collected in the Philippines, at this time it is extremely unlikely that you will have the chance to see one of these in your local aquarium store. Photo courtesy of John Randall.

In the Home Aquarium

Juvenile Ringed wrasses can adapt well to the home aquarium, but this is not usually the concern. Of the utmost importance to this genus are the aquariums' size and their potential tankmates. By nature, wrasses are active fish and are almost always "on the go." Their active nature, coupled with an adult size of over 12", combine to warrant an aquarium of substantial size. Although witnessing a juvenile grow into a 12" male is unlikely in the home aquarium, these fish nonetheless can become very large, and usually do so in a short amount of time. I have generally shied away from recommending the aquarium size required to allow for successful maintenance of a healthy fish in my past columns, and I will continue to do so in this column, mostly because no one can agree on what defines "large" or "adequate." I will, however, note that their swimming characteristics and overall size are similar to those of Surgeonfish. Whereas juveniles will do well in small aquariums initially, plans for their potential growth within an optimally-sized habitat should be in place prior to their purchase. If an aquarium of at least several hundred gallons is not possible, it is best to avoid this fish, as anything less will likely result in stunted growth, unnecessary stress, and an early death from stress and stunted-growth related issues.

Despite the noxious mucus on the skin of Gobiodon species, they will likely be made a quick meal in the presence of an adult Hologymnosus. Photo courtesy of Greg Rothschild.
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Assuming a large tank is in the works, let's forge ahead. If you read above about their natural diet in the wild, then you should no doubt understand why their potential tankmates are a concern. Anything resembling a fish or mobile invertebrate that they can eat, they will eat! This includes shrimp, crabs, starfish, and especially fish. It is best to plan for a fish-only aquarium with tankmates consisting of other large predators. Lionfish, morays, and surgeonfish are but a few recommendations of fish to consider. For a full list, see the compatibility chart below.

Compatibility chart for Hologymnosus species:

Fish

Will Co-Exist

May Co-Exist

Will Not Co-Exist

Notes

Angels, Dwarf

 

X 
 

Adult Hologymnosus may harass or consume, while juveniles should mix well.

Angels, Large

X

 
 

Should co-exist well.

Anthias

 
X

 

Adult Hologymnosus may harass or consume, while juveniles should mix well.

Assessors

 
 

X

Will be consumed or harassed by Hologymnosus species.

Basses

 

X
 

Adult Hologymnosus may harass or consume, while juveniles should mix well.

Batfish

 

X

 

Adult Hologymnosus may harass or consume, while juveniles should mix well.

Blennies

 
 

X

Will be consumed or harassed by Hologymnosus species.

Boxfishes

X
 

 

Do not add juvenile boxfish with established Hologymnosus.

Butterflies

X

 
 

Should co-exist well.

Cardinals

 
 

X

Will be consumed or harassed by Hologymnosus species.

Catfish

 

X
 

Keep adult catfish with adult Hologymnosus, and juvenile catfish with juvenile Hologymnosus.

Comet

 

X

 

Adult Hologymnosus may harass or consume, while juveniles should mix well.

Cowfish

 
 

X

Will be consumed or harassed by Hologymnosus species.

Damsels

 

X

 

Adult Hologymnosus may harass or consume, while juveniles should mix well.

Dottybacks

 

 
X

Will be consumed or harassed by Hologymnosus species.

Dragonets

 

X

 

Adult Hologymnosus may harass or consume, while juveniles should mix well.

Drums

 
X

 

Do not add juvenile drums with established Hologymnosus.

Eels

X

 
 

Should co-exist well.

Filefish

X
 

 

Should co-exist well.

Frogfish

 
 

X

Frogfish will try to consume juvenile Hologymnosus.

Goatfish

X
 

 

Should mix well, especially with female Hologymnosus.

Gobies

 
 

X

Will be consumed or harassed by Hologymnosus species.

Grammas

 

 

X

Will be consumed or harassed by Hologymnosus species.

Groupers

X

 

 

Should co-exist well. Do not place juvenile Hologymnosus with adult groupers.

Hamlets

X

 

 

Should co-exist well.

Hawkfish

 

X

 

Avoid the smaller hawkfish with adult Hologymnosus.

Jawfish

 

 

X

Will be consumed or harassed by Hologymnosus species..

Lionfish

X

 
 

Should co-exist well.

Parrotfish

X

 
 

Should co-exist well.

Pineapple Fish

X

 

 

Should co-exist well.

Pipefish

 
 

X

Will be consumed or harassed by Hologymnosus species.

Puffers

X

 

 

Should co-exist well.

Rabbitfish

X

 
 

Should co-exist well.

Sand Perches

X
 

 

Should co-exist well. Do not mix juvenile Hologymnosus with adult sand perches.

Scorpionfish

X
 
 

Should co-exist well. Do not mix juvenile Hologymnosus with adult Scorpionfish.

Seahorses

 
 

X

Will be consumed or harassed by Hologymnosus species.

Snappers

X

 

 

Should co-exist well. Do not mix juvenile Hologymnosus with adult Snappers.

Soapfishes

X

 

 

Should co-exist well.

Soldierfish

X

 

 

Should co-exist well.

Spinecheeks

X
 

 

Should co-exist well.

Squirrelfish

X

 

 

Should co-exist well.

Surgeonfish

X

 
 

Should co-exist well.

Sweetlips

X

 

 

Should co-exist well. Do not mix juvenile Hologymnosus with adult Sweetlips.

Tilefish

 

X
 

Juveniles of each will mix, but avoid keeping adult Hologymnosus with Tilefish.

Toadfish

 
 

X

Toadfish will likely consume Hologymnosus.

Triggerfish

 

X

 

Some Triggerfish refuse to accept any tankmates, while others are ideal candidates. Research Triggerfish requirements prior to purchase.

Waspfish

 
X

 

Juvenile Hologymnosus are at risk of being consumed.

Wrasses

 

X

 

Avoid the smaller "reef safe" wrasses, they will be harassed or consumed.

Note: While many of the fish listed are good tank mates for Hologymnosus species, 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. Additionally, as predators of small fish Hologymnosus may feed upon any juvenile fish, even those listed above as co-existing well.

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Larger fish, such as this Sohal Tang, are a good choice to share the aquarium with Ringed Wrasses.
Any fish large enough to not get pestered or eaten, and one that is an aggressive eater at feeding
time should do well with Hologymnosus species. Photo courtesy of Greg Rothschild.

A minimum of 2" of sand should be present in an aquarium housing juveniles and up to 4 or 5" should be provided for adults. This will be for the fish to dive into and sleep for the night. You can expect your Ringed wrasse to go to sleep, and wake up, at nearly the same time each day. Their internal clock is amazingly predictable. At first, this might be a problem, as they are still functioning on Indo-Pacific time. As the days and weeks pass, however, the fish will slowly readjust their schedule to more closely resemble the tank's photoperiod. Additionally, if the need to remove the fish from your aquarium should ever arise, it will be easiest to do so in the evening by capturing the fish while it sleeps under the sand. To make capture easier, be advised that most wrasses will sleep in the same general area night after night.

As with any new fish purchase, inspect Ringed wrasses carefully. Due to their natural instinct to dive into the sand, it is not uncommon for them to arrive at the fish store with damaged mouths. This is often the result of shipping stress where they constantly try to bury themselves in the shipping bags. Of course, you should inspect the remainder of the fish's body as well. Check over its fins and tail carefully for tears or unnatural growths. If the fish generally appears healthy, make sure it is eating prepared foods. Juveniles will require smaller foods such as brine or mysid shrimp, but as they age they will begin to need larger food items. As adults, it is likely they will prefer frozen/thawed silversides over all other foods.

Meet the Species

Only two of the four species make it into local aquarium stores with any regularity. Due to its wide-ranging geographical distribution, Hologymnosus annulatus is the most commonly available fish of this genus. Possibly because it is so much more readily available than the other species in the genus, H. annulatus and the entire genus share the same common name, the Ringed Wrasses. At roughly four inches the juveniles will begin their color and sexual transformation. This will first become noticeable to the fish keeper when the black stripe separates into short bars. By the time your fish reaches 10 inches it should be, or will begin changing into, the terminal phase male.

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Although shown as Hologymnosus doliatus on webpages across the internet, this fish is actually H. annulatus, the Ringed Wrasse. A juvenile is pictured above. As it begins to age the intermediate color stage will begin to take shape usually around 4 or 5 inches of length (bottom photo). Photos courtesy of John Randall.

The Candycane wrasse, Hologymnosus doliatus, can also be found by dedicated hobbyists if a long and hard search is sustained. These juveniles begin their transformation at a smaller size than do those of H. annulatus; at three inches the change should begin. Males have been noted to be as small as seven inches, although the color pattern shift noted in terminal phase H. doliatus doesn't begin until around nine inches.

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The adult male Hologymnosus doliatus is certainly a sight to behold. Unfortunately,
at a maximum size of around 16 - 18 inches, they are too large for most home aquariums.
Even though these species are less likely to consume other tankmates than their close
cousins, it is still extremely risky to mix smaller fish with them.
Photos courtesy of John Randall.

Hologymnosus longipes, the Sidespot wrasse, is fairly common in the wild, but it happens to be found in areas not prone to collection for the hobby. As a result, this fish is a rare occurrence in the aquarium trade. It is noted to quickly change color patterns depending on whether it is over white sand or deep, dark blue ocean water or even dark rubble. The fish can reportedly change from a white with pale orange stripes to a pale blue-purple body with dark orange stripes in a matter of seconds as the fish swims from one area to another (Randall and Yamakawa, 1988).

The remaining species, Hologymnosus rhodonotus, is not available in the aquarium hobby. Research efforts have been able to procure only a few individuals. As a result, very little is known about these fish other than their apparent scarcity.

Conclusions

There are those fish that for whatever reason just do not belong in a reef aquarium. Hologymnosus species are just one such example. Their appetite will eventually drive them to attempt to consume all mobile invertebrates such as crabs, snails, starfish, and shrimp, while they will also extremely limit the aquarist's options of other fish for the aquarium. Juveniles may do well in reef aquariums for a period of time, but eventually their natural instincts will begin to show. If you desire to maintain one of these wrasses, it would be best to plan a large fish-only aquarium from the start.



If you have any questions about this article, please visit my author forum on Reef Central.

References:

Baensch, H.A. 1994. Baensch Marine Atlas, Volume 1. Microcosm. Shelburne. 1215 pp.

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

Lieske, E. and R. Myers, 1994. Collins Pocket Guide. Coral reef fishes. Indo-Pacific & Caribbean including the Red Sea. Harper Collins Publishers, 400 p.

Michael, S.W. 1998. Reef Fishes Volume 1. Microcosm. Shelburne. pp. 624.

Michael, S.W. 1999. Marine Fishes: 500 + Essential-To-Know Aquarium Species. Microcosm. Shelburne. pp. 448.

Randall, J.E., 1982. A review of the labrid fish genus Hologymnosus. Rev. fr. Aquariol. 9(1):13-20.

Randall, J.E. and T. Yamakawa, 1988. A new species of the labrid fish of the genus Hologymnosus from the Western Pacific, with notes on H. longipes. Rev. fr. Aquariol 15(1):25-30.

Randall, J.E., G.R. Allen and R.C. Steene, 1990. Fishes of the Great Barrier Reef and Coral Sea. University of Hawaii Press, Honolulu, Hawaii. 506 p.




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A Ring Around a Wrasse: The Genus Hologymnosus by Henry C. Schultz III - ReefKeeping.com