Do you call them Hepatus tangs? Some probably prefer Palette tang or even Blue Palette tang. Others will not recognize the name until you mention Flagtail tang or Hippo tang. Did someone yell out Wedge-tail tang? I was first introduced to them as Pacific Blue tangs, and thus that is what I most often call them. Of course, to compound this confusion, you can insert 'surgeonfish' or even 'doctorfish' for 'tang' in any of these examples. Whatever you call it, the fish remains the same: a bright blue colored fish with black and yellow accents that might be the most popular Surgeonfish in the marine aquarium hobby. For March, I'll take a look at Paracanthurus hepatus (insert your favorite name here).

Meet the Family

The Pacific Blue surgeonfish is a member of the family Acanthuridae. This family consists of three sub-families, six genera, and seventy-two species (Michael, 1998). Every species possess a potent weapon just forward of the base of the tail, on an area known as the caudal peduncle. This weapon is similar to a dagger and consists of modified scales. Extensive tests have been inconclusive in showing any sort of venom associated with this knife-like spine, but it is important to note that every fish cut with the caudal peduncle from members of the sub-family Prionurinae have died as a result of the wound (Baensch, 1994). Luckily, fish from the sub-family Prionurinae rarely make it into the hobby. Ichthyologists use the caudal peduncle to place each member into one of the three sub-families. In all three sub-families the dagger is attached closest to the base of the tail, and extends toward the front of the fish. Paracanthurus hepatus is a member of the sub-family Acanthurinae. These members have a single caudal peduncle on each side that folds safely away until needed. In the sub-family Nasinae the caudal peduncle is fixed, and either 1 or even 2 of these daggers may be found on each side of the fish. Finally, the last sub-family, called Prionurinae, has three to ten bony plates alongside the peduncle (Michael, 1998) and can have from three to six caudal peduncles per side, though three is most common (Baensch, 1994).

Paracanthurus is the only genus from Acanthuridae to be monotypic, meaning containing only one species. At one point Paracanthurus contained two species, but P. theuthis was later proven to be a synonym of P. hepatus. Also, at one point Paracanthurus was considered invalid, and this fish was recognized as Teuthis hepatus. This disagreement has been settled, and we now recognize the original 1766 description by Linnaeus.

In the Wild

The common name 'Pacific Blue tang' hopefully indicates to you which ocean this fish originates from, however, the Pacific Ocean is a rather large body of water. If you truly wanted to view this fish in its wild habitat you would find yourself most likely in Palau, Bali, or the Philippines, but you could likely find it anywhere from East Africa to the Great Barrier Reef, and into Southern Japan. In its native waters Paracanthurus hepatus can be found as shallow as 10 feet and as deep as 130 feet, though they are most common somewhere in the middle of those two depths. They tend to congregate where there are abundant food supplies, crystal clear water, and an aggressive current. They will be found at these depths foraging on zooplankton over outer reef slopes.

Juveniles tend to stay closer to cover, usually found three to ten feet over the reef. The juveniles will associate with Pocillopora eydouxi and use this coral for shelter by diving into the branches and wedging themselves tight into the coral. On occasion they may also use various Acropora for this purpose. Adults, however, can be located up to 30 feet or more above the reef feeding and usually do not fit well into corals, and thus they primarily use larger crevices in the reef structure to wedge into and hide themselves (Coral Realm).

Juveniles are usually found in loose aggregations while feeding, and as they age will adapt into a more solitary lifestyle. By the time they are adults, the only time they are not solitary is when they are in small harems during mating season. The rare occasion of 30 or more adults forming a school is likely a result of the fish teaming up to overrun an aggressive defender of a territory that has abundant food available.

Adults will join into groups of one male and two to seven females during the mating season, which extends from February through March in Micronesia. Males will aggressively defend their small harem from rival males, though females may move freely from one group to another. Several sub-groups can be present in the same location, though, if ample room is available; 100m² to 200m² provides enough room for five to eight sub-groups to maintain adequate territories (Robertson, 1983). Spawning takes place in pairs only, at which time the male's coloration fades everywhere with the exception of the black markings and the head. The female changes color by altering the black to a gray. This sexual dichromatism exists only during spawning and, besides the spawning, no sexual dichromatism exists. There is a sexual dimorphism however, with the males being slightly larger than the females.

In the Home Aquarium

As a whole, Hippo tangs do very well in aquariums. With few exceptions, they are considered hardy and durable aquarium fish. A few criteria need to be met to ensure successful husbandry, however.

I am sure that after a year of saying this I am starting to sound like a broken record, but the story remains the same for most any aquarium fish. The first consideration is a well-aged and stable aquarium. Surgeonfish are definitely not an exception, and in particular, Paracanthurus hepatus requires stable water conditions. This fish has been garnished the nick-name of 'ich magnet' by many aquarists, thanks to the likelihood of it developing a case of Cryptocaryon irritans when newly introduced to an aquarium. If the aquarium has appropriate water conditions, which mirror natural sea water as closely as possible, and suitable tank mates, which will not pester the new addition, it should recover from this affliction with little intervention from the hobbyist. Watch closely for a secondary bacterial infection, which is a sure sign that the fish cannot overcome this illness without your help. Upon first observation of this infection, treatment in a quarantine tank should start immediately.

The obvious next consideration is tank mates. Overall, Hepatus surgeonfish will not bother other tank inhabitants. Except for the rare occasion, they will not bother sessile invertebrates. Crabs, snails, and other mobile invertebrates will also be largely ignored. This combination makes them perfect inhabitants for a reef aquarium. In regards to finned friends, the Palette tang will not bother anyone, with the possible exception of the lionfish, as sometimes it's fluttering fins are too much to resist. In general, Palette tangs are quite skittish. Hard to imagine from a fish that spends its afternoons 30 feet above cover searching for food. Or is it? Perhaps the extended distance required in finding adequate food is actually the root cause for the skittish behavior. Any perceived threat results in the immediate dash for suitable cover. Not hard to understand considering cover is usually a good ways off. Unfortunately, this instinct carries over into the home aquarium. As a result, active swimming fish may inhabit the acclimation process of newly arrived Hepatus surgeonfish. If the Hepatus tang is the most active fish in the aquarium when it is added, it will adapt to captivity quicker. Larger or more active fish can be added to the aquarium once the Hepatus has acclimated to aquarium conditions, however. At least for the first week or two you can expect Paracanthurus hepatus to spend more time pinned into rockwork than actually swimming in the aquarium. As it settles in you can expect this to shift in the opposite direction until finally the fish rarely hides. If other large, active fish are present in the aquarium, it may never fully adjust, and it may spend an appreciable amount of time in seclusion. Conspecifics and other larger fish may force the need for defensive measures. The defensive mechanism of Palette tangs is the aforementioned caudal peduncle, which, like all members of the sub-family Acanthurinae, is kept tucked away until an 80-degree twist of the tail reveals the deadly weapon. Speaking from personal experience with Hippo tangs, the dagger easily breaks the skin of a human hand, and remains painful for over a week. Lastly, though it should be obvious, do not mix juvenile Hippo tangs with larger fish capable of swallowing them.

Compatibility chart for Paracanthurus hepatus:

Fish	Will Co-Exist	May Co-Exist	Will Not Co-Exist	Notes
Angels, Dwarf	X			Should be excellent tank mates.
Angels, Large	X			Should be excellent tank mates.
Anthias	X			Should be excellent tank mates.
Assessors	X			Should be excellent tank mates.
Basses	X			Should be excellent tank mates.
Batfish	X			Should be excellent tank mates.
Blennies	X			Should be excellent tank mates.
Boxfishes	X			Should be excellent tank mates.
Butterflies	X			Should be excellent tank mates.
Cardinals	X			Should be excellent tank mates.
Catfish	X			Should be excellent tank mates.
Comet	X			Should be excellent tank mates.
Cowfish	X			Should be excellent tank mates.
Damsels	X			Should be excellent tank mates.
Dottybacks		X		Some dottybacks require dedicated aquariums.
Dragonets	X			Should be excellent tank mates.
Drums	X			Should be excellent tank mates.
Eels	X			Should be excellent tank mates.
Filefish	X			Should be excellent tank mates.
Frogfish	X			Should be excellent tank mates.
Goatfish	X			Should be excellent tank mates.
Gobies	X			Should be excellent tank mates.
Grammas	X			Should be excellent tank mates.
Groupers	X			Should be excellent tank mates.
Hamlets	X			Should be good tank mates.
Hawkfish	X			Should be excellent tank mates.
Jawfish	X			Jawfish in first.
Lionfish		X		Should co-exist fine, but watch for harassment from tang.
Parrotfish	X			Should be excellent tank mates.
Pineapple Fish	X			Should be excellent tank mates.
Pipefish			X	Pipefish require dedicated aquariums.
Puffers	X			Should be excellent tank mates.
Rabbitfish	X			Should be excellent tank mates.
Sand Perches	X			Should be excellent tank mates.
Scorpionfish		X		Same as lionfish.
Seahorses			X	Seahorses require dedicated aquariums.
Snappers	X			Should be excellent tank mates.
Soapfishes	X			Should be excellent tank mates.
Soldierfish	X			Should be excellent tank mates.
Spinecheeks	X			Should be excellent tank mates.
Squirrelfish	X			Should be excellent tank mates.
Surgeonfish		X		Hippo in first.
Sweetlips	X			Should be excellent tank mates.
Tilefish	X			Should be excellent tank mates.
Toadfish	X			Should be excellent tank mates.
Triggerfish		X		Some triggerfish require dedicated aquariums.
Waspfish	X			Should be excellent tank mates.
Wrasses	X			Should be excellent tank mates.

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

Another consideration to ponder is food choices. As juveniles, Hepatus tangs are nearly strict planktivores. However, as they age into adulthood, some individuals may begin to supplement their diet with various algae such as Caulerpa. This diet should be mimicked in the home aquarium. Large portions of the diet should consist of Mysis shrimp, and as the fish ages you should begin to supplement the diet with various dried algae such as nori. Your fish may or may not take to eating algae. Most any food presented in the water column will eventually be taken, including enriched brine, and flake. However, the staple of the diet should always remain Mysis or plankton. My personal favorite is freeze-dried plankton soaked in any of the widely available food vitamin supplements. The diet is an important consideration, as Paracanthurus hepatus are extremely prone to Head and Lateral Line Erosion (HLLE). Though the root cause of HLLE has yet to be determined, most researchers agree that an insufficient diet plays a large role. Many times when the diet was improved, the condition reversed and cured itself.

Finally, no discussion of Surgeonfish would be complete without talking about tank size. This is an often-debated topic that usually becomes heated on both sides of the fence. Most everyone can agree, however, that the larger the aquarium the better off the fish will be. Many authors recommend certain "minimum" aquarium sizes; though it seems no one can agree on exactly what the "minimum" is. Realistically speaking, the "minimum" environment for these fish is any aquarium the owner feels morally and ethically comfortable putting the fish into. Each hobbyist must come to his or her own conclusions, but hopefully these decisions are made only after reviewing the data that is readily available.

Scroll back up to the paragraph discussing mating rituals and you'll see that Robertson has already given us a reference for territorial dimensions, at least during the mating season. If you take the minimum number of animals (15 - one male, two females, per group with five sub-groups) divided by the minimum defined territory (100m²) you'd discover the groups maintained a minimum of 20m² each or a minimum of 6.66m² per animal. For those of you not good with transcribing meters into feet, 6.66m² works out to be roughly 21.8f² per animal. That would be an aquarium roughly 7 feet long and 3 feet wide. Hmmm. For the sake of argument let's take the maximum number of individuals, packed into the largest territory known. Sixty-four fish (one male, seven females per group, and eight sub-groups) packed into 200m². This works out to 25m² per sub-group, or just over 3m² per animal or about 10f², or about the size of any of the commercially available 125-gallon aquariums. Hence, I would propose this is a good starting point as the absolute minimum aquarium size for any solitary individual.

Let's not forget, however, two important factors. First, this fish only spends two months of the year in such a confined space. The remaining ten months of the year are spent cruising 30 feet above the reef, usually cruising up to 30 meters in one direction before reaching the edge of their territory (Randall, pers. comm.). Second, even when in mating season and defending a territory of a given space, this does not mean this is the only distance they swim. For example, the fish may defend an area equivalent to seven feet by three feet, but this does not mean the fish swims in a circle that measures these dimensions, much like it would have to in your aquarium. Instead, this means it requires this much space as a minimum between its next conspecific. What is more likely the case is it defends the minimum territory as it roams about the reef ledge with the harem, or as it swims to the next closest harem.

What is known from keeping these fish in aquariums smaller than several hundred gallons is that the end result is a fish with stunted growth. The extent of the growth stunt is directly proportionate to the aquarium size. Following Choat and Axe (1996) and the understanding that Acanthurids obtain 80% of their growth in their first 15% of life, you can get an idea of how fast they should be growing in your aquarium. Combine this with an expected 35 years of age per Acanthurid (Chaot and Axe, 1996), we come up with 80% growth obtained in 5.25 years. Let's take this a step further and plug in the expected maximum size for Paracanthurus hepatus, roughly 12". After doing the math you should get the answer of Paracanthurus hepatus obtaining 9.6 inches at 5.25 years of age. Following the same reference, which states the first 80% growth is fairly consistent, you can take it yet one step farther to learn that your Paracanthurus hepatus should be 1.8 inches after the first year, and continue to grow nearly two inches every year from then until five years of age, where their growth will slow and nearly stop, at which time it should be nearly ten inches. You could also use this same formula when trying to obtain an age of a newly imported specimen.

At this point you should be adequately prepared to determine if your Paracanthurus hepatus has experienced stunted growth. The decision on how to handle this situation is up to you.

Reproduction In The Home Aquarium

Reproduction in the home aquarium has not yet been accomplished. For the hobbyist wishing to attempt successful mating in their home aquarium, please view the requirements listed above for space per individual, as well as the number of individuals required. This would almost certainly preclude successful mating. Hippo tangs are pelagic spawners and the eggs spend a considerable amount of time in a platonic stage, which makes it very difficult to successfully rear the fry if the spawning does occur. Continued advancements in food products for platonic larvae may someday make this possible.

However, the good news is that captive-reared Paracanthurus hepatus are available. Do not confuse the terms captive-bred and captive-reared. Captive-bred means bred in captivity. That has not yet been possible with Paracanthurus hepatus. Captive-reared, however, means spawned in the wild and captured at the larval/post-larval stage and grown out in a protected "farm" of sorts. Once roughly ½ inch in length they are then shipped from the Solomon Islands to the United States and grown another ½ - ¾ of an inch. At that time they are then moved to the wholesale/retail level and are eventually offered for sale to the hobbyist at a size of roughly 1 - 1.5 inches in length. These captive-reared fish have proven to be excellent at adjusting to home aquarium conditions, much more so than their adult conspecifics.

Conclusion

It doesn't matter which name you call it, they all refer to an unmistakable fish that has won over the hearts of many hobbyists. The care of these beauties is unlike most other surgeonfish in that they require large amounts of meat-based foods. When given proper care they are hardy inhabitants of a home aquarium, though they are fast growers. This brings up the next consideration in tank size. Only you can decide what type of life your fish will live. Lastly, please make an attempt at acquiring a captive-reared specimen.

References:

Baensch, H.A. 1994. Surgeonfish. 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.

Choat, J.H. and L.M. Axe.1996. Growth and longevity in acanthurid fishes; an analysis of otolith increments. Marine Ecology Progress Series; Volume 134, Issue 1-3, Pages 15-26.

Lieske, E. and R. Myers, 1994. Coral reef fishes. Indo-Pacific & Caribbean including the Red Sea. Haper Collins Publishers, 400 pp.

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

Michael, S. W. 1999. Surgeonfish. Marine Fishes: 500 + Essential-To-Know Aquarium Species. Microcosm. Shelburne. 447 pp.

Myers, R.F., 1991. Micronesian reef fishes. Second Ed. Coral Graphics, Barrigada, Guam. 298 pp.

Randall, J.E. 1955. A revision of the surgeonfish genera Zebrasoma and Paracanthurus. Pac. Sci. 9:396-412.

Randall, John E. 1981. Palette surgeonfish, Paracanthurus hepatus. FAMA 3/81.

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