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Issue: February 2010

The Achilles Tang Acanthurus achilles

Author: Jeremy Gosnell

GOSN T 0210
Photographer: James Fatherree
This sleek surgeonfish carries a multitude of caretaking requirements, making it a challenging but rewarding specimen for advanced marine aquarists.

Sometimes when we look at the aquarium hobby, it seems as if Mother Nature has a unique sense of irony. Some of the hobby’s most beautiful marine specimens are also the most difficult to keep. Orange-spotted filefish Oxymonacanthus longirostris, mandarinfish Synchiropus splendidus, and Moorish idols Zanclus cornutus all fall into this category. They are animals that are strikingly beautiful but often very difficult to keep alive in the aquarium setting. While a handful of thoughtful and prudent aquarists can often achieve some measure of success with these species, the majority of specimens do not survive long in home systems.

The Achilles tang Acanthurus achilles also represents a species that is gorgeous and unique but also very challenging to keep healthy. Even its name has a certain mystique, paying homage to the Greek hero of the Trojan War. But sadly, the fish also shares that hero’s tragic flaw of vulnerability—while Achilles’ heel was the otherwise indestructible warrior’s weak point, it is feeding, space, stress, and the water’s oxygen content that appear to make the Achilles tang very hard to acclimate and keep alive in the aquarium.

So what can be done to successfully keep an Achilles tang alive and healthy? Are they truly impossible to keep? What factors from the Achilles tang’s natural environment contribute to their difficult nature in our aquariums?

The Achilles Challenge

Calling the Achilles tang one of the more demanding members of the Acanthurus clan is an understatement. Like many surgeonfish, these guys are highly susceptible to ich and head-and-lateral-line erosion. Many of the diet-related preventatives that are implemented work well with Achilles tangs, though getting them to eat can be a challenge as well. To make matters worse, Achilles tangs tend to be highly aggressive toward other tang varieties and are often downright deadly to other members of their own species. They can also be very hard to successfully acclimate to aquarium life in the first place.

Despite these difficulties, it is hard to argue against the Achilles tang being one of the sleekest looking members of the surgeonfish classification. Their dark (black to brown) bodies and orange tail spot are perfect complements that make the fish a unique and attractive addition to any reef or fish-only aquarium. But the reality is that these fish are so difficult to maintain in aquariums that many retailers offering replacements for perished animals suspend that policy when selling this species.

Environmental Factors

Achilles tangs inhabit the area of Pacific coral reefs called the surge zone or reef crest. Here water breaks over a shallow portion of the reef, creating strong currents and filling the water with oxygen. You have probably seen video of a coral reef crest, where water breaks with force and you can often see the fish beneath being pulled to and fro in the current. Air bubbles often cascade throughout the water column as each wave breaks.

Naturally, replicating this turbulent flow helps the fish acclimate to aquarium life, but unfortunately this can present a two-fold problem for the aquarist. First, many coral and invertebrate species do not prefer such a strong current. For instance, large-polyped stony (LPS) corals often prefer a mild or gentle current.

Secondly, many fish species compatible for an aquarium housing an Achilles tang do not inhabit the reef crest and prefer a milder current. When making the decision to keep one of these animals, the aquarist needs to make some sacrifices or find a common ground. Researching corals and fish that inhabit the reef crest and will not cause compatibility issues with an Achilles tang can increase the probability of success.

Another environmental factor that must be taken into consideration when housing an Achilles tang is space. Like all surgeonfish, Achilles tangs are free swimmers. In my experience these fish struggle more than other species when adjusting to the confines of the aquarium. I have noticed that Achilles tangs will pace back and forth in the aquarium if there isn’t enough space for them to feel comfortable. They often become so stressed that other aquarium residents begin to harass them.

Offering an Achilles tang ample space is a vital to success. An aquarium of 100 gallons or more is necessary, and more space is better. Additionally, opting for a tank that is wide from side to side and thin from front to back is better than choosing a tall tank.

Aquascaping your tank’s interior to offer open swimming spaces with lots of hiding spots should suit an Achilles tang better than a reef piled to the brim with live rock. Remember that A. achilles is a species of fish that requires an aquarium planned around its well-being. This means that the tang will be the heartbeat of the tank, with all the other variables worked in to suit the fish’s needs.

Space becomes a concern when quarantining a new specimen. Many aquarists use a small 20- or 30-gallon aquarium to quarantine new arrivals and prevent a disease outbreak in their display tank. Any new fish requires a quarantine period of 14 to 30 days. The problem is that the close confines of a quarantine tank can greatly stress an Achilles tang and cause larger problems. Like all fish, an Achilles tang must be quarantined, but unlike many fish, it requires a large tank of at least 50 gallons.

Diet and Feeding

The Achilles tang requires a diet very similar to many of the other surgeonfish kept in captivity. These fish are primarily herbivores, so offering them a good crop of freeze-dried algae sheets coupled with an aquarium containing natural-growing algae works well. A. achilles can be a very problematic feeder when introduced to the aquarium. Unlike many surgeonfish that readily accept prepared aquarium foods, the Achilles tang can be picky about what it will accept—if it accepts anything at all.

Using frozen fare like mysis shrimp can usually entice these animals to eat. The problem is that such frozen food products do not usually offer the necessary nutrition for this fish—what it needs is macroalgae. I have found that using a rubber band to attach algae sheets to the rockwork in the aquarium works better at enticing Achilles tangs to eat than just sticking an algae clip to the front glass.

Spirulina, zucchini, broccoli, and dark green lettuce are all good supplements to the Achilles tang’s diet. I have also had success at preventing parasitic outbreaks by feeding an anti-parasitic food, but I prefer pellet-based foods that do not contain any antibiotic or anti-parasitic chemicals but are simply high in protein and enriched with garlic. Freeze-dried algae infused with garlic can now be purchased, and this will also help prevent parasite-related issues.

Stocking and Tankmates

The Achilles tang can really cause difficulties when it comes to finding suitable tankmates for it. There is a great variation among individual fish. Some specimens I have kept are the dominant fish in the tank, asserting their aggression with violent displays to nearly all of their comrades in the aquarium. On the flip side, I have kept specimens that were easily stressed by nearly all the other fish in the tank.

I prefer a gentle approach when keeping an Achilles tang. Rule number one is that there can be no other surgeonfish in the aquarium of any species. Even a Zebrasoma species, such as a yellow tang, can cause an upset to the balance. I have found that other surgeonfish are either too aggressive toward the Achilles tang, not allowing it proper acclimation time, or the Achilles is too aggressive toward the other species.

I also don’t like to keep these fish with aggressive species such as triggerfish. It seems as if the tang’s stress often gets the best of it, and then aggressive fish move in to make matters worse by pestering the tang. Keeping an Achilles tang in a lightly stocked reef with small and docile species seems to be a good avenue for success.

As I said earlier, an Achilles tang really is a species that needs the aquarium planned around it. Luckily these fish are exotic and exciting enough to make all the effort worthwhile, and the proper setup will assist you in keeping your tang healthy. For example, having cleaner shrimp and fish present can keep the Achilles parasite-free. I have found that skunk cleaner shrimp Lysmata amboinensis and neon cleaner gobies Elacatinus (Gobiosoma) oceanops work well to service the Achilles tang. Sometimes hungry Achilles tangs are reported to nip at large-polyp stony corals, but in my experience dining on coral has not been a problem with this species.

Special Considerations

It may appear that keeping an Achilles tang is a monumental task that is likely to result in failure, but knowledge is the key. In over 10 years as a marine aquarist, I have purchased a total of two Achilles tang specimens. The first attempt resulted in quick and utter failure. The second was met with long-term success, a success I attribute to my taking a well-planned and highly cautious approach to keeping the animal healthy.

You must of course acquire a healthy specimen from the outset. Dealing with a reputable and trusted marine dealer is important. I would recommend a dealer that quarantines stock before sale. I would also ask the dealer to feed the fish to ensure that it is taking some form of food (frozen, algae, or otherwise) before taking it home. A specimen that is already eating is much more likely to make the transition to your aquarium successfully.

When we look at all the potential problems existing with this species—susceptibility to parasites, feeding difficulties, aggressive or passive nature regarding tankmates—it might seem crazy for anyone to even think about housing one. The reality is, as with all potential aquarium tenants, some forethought, planning, and strategy go a long way when keeping an Achilles tang.

As more aquarists work to keep difficult species, the requirements these animals have and how to meet them are being worked out. But while there has been a tremendous amount of progress made over the years, there is still a long way to go. Keeping an Achilles tang should only be attempted by aquarists who have the experience, knowledge, and proper aquarium system to keep the animal healthy long-term. Unfortunately, considering the Achilles tang’s steep requirements, those aquarists tend to be the exception and not the rule. 

See the full article on TFH Digital http://www.tfhdigital.com/tfh/201002/#pg89

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