Why do the tang police exist?


I don’t really consider myself the tang police. By that, I don’t head out on the internet or to local fish shops, with the sole goal of telling people not to keep tangs under certain conditions. However, I do advocate keeping a healthy, sustainable aquarium based on the principles I have personally found useful during 20 years of keeping marine fish. There are just some things that work and others that don’t. One thing I’ve never witnessed working long-term is keeping a surgeonfish (or any large species) under inappropriate, over-crowded conditions. It always leads to problems, often for both the fish and aquarist. In this regard, I often support the work of the tang police, even if their efforts are too concentrated on one issue and could be broadened to include the basics of responsible reef keeping. For everything we know about marine fish in captivity, there is something that we don’t know. The jury is still out on what causes head and lateral line erosion (HLLE), we still don’t understand why species like Moorish idols fail to thrive in aquariums and the effects of certain aquarium conditions on marine species are murky at best.

Given surgeonfish’s unique and desirable traits, it’s worth understanding how they effect a reef aquarium and how a reef aquarium affects them. Aquarists need to understand the limitations that come with keeping surgeonfish. As a species, surgeonfish bring with them a host of challenges beyond their susceptibility to external parasites. They are not ideal reef tank dwellers, yet every reef tank seems to have at least one. What is it about surgeonfish that makes them such an often discussed and often contested and policed species among marine aquarists.



When I ask most marine aquarists what their favorite fish species is, often they reply surgeonfish. Tangs (as they’re often called) strike a balance between beauty and grace, with a hallmark dash of personality. They rank among some of the most beautiful marine fish and are featured in advertisements and marine centered TV programs frequently. They’ve even assumed the role of childhood icon as the star character in a Disney film series. Tang’s popularity in marine aquariums is only matched by that of clownfish. Everyone seems to have one and those that don’t want one.

Acanthuridae is the family name that covers 82 existing species of surgeonfish. Depending on where you are in the world, or what facet of marine study you follow, these fish may be called unicorn fish, surgeonfish or the infamous tang(s). Their most distinctive feature is without a doubt scalpel like spines and some species’ spines retract, while others remain in a fixed position, but always lurking just in front of the tail fin. These spines are very sharp, easily capable of slicing open human skin and deadly to tank mates. A wound from a surgeonfish’s scalpel often leads to bacterial infection and spells disaster for the inflicted fish. Usually tangs sport oversized dorsal, anal and caudal fins, extending either the length of the body or appearing like wide sails around the fish. Most tangs have small mouths with a single row of teeth, specially designed for scraping algae off rocks or another substrate.

In the wild, some surgeonfish are solitary feeders that comb the reef for algae alone. Other species or individuals travel in a school, believed to be a defensive mechanism for overwhelming damselfish that aggressively protect their algae laden nests from intruders. Most tangs reach a size of just over six inches, while a few others can grow beyond a foot in length. Naso tangs and various unicorn fish are known to reach lengths of two to three feet, making their suitability for home aquaria of any size questionable.

Tang’s scientific family name is derived from the Greek words akantha and thora, translated to mean thorn and tail, or thorny tail.

In the aquarium:

Some marine species adjust to captive life with ease, often retaining the same behaviors they display in the wild. Clownfish for example will take up residence in an anemone and given good conditions and a suitable partner, readily spawn. Gobies and blennies commonly carve out a small slice of captive reef and assume their natural action of sifting sand or bonding with a shrimp. Even various cleaner organisms commonly set-up shop within the aquarium and provide the same service there, as they would on a wild reef. Often species that retain a tight territory on wild reefs, adjust well to the confines of captive life.

However, tangs, like other open water swimmers, seem uncomfortably aware of their captive fate. When first introduced to an aquarium, they spend the majority of their time hiding. Within time that is replaced with an uncomfortable pacing and even after years in a large aquarium, they tend to be jumpy and on-edge. Some long-time aquarists theorize that tangs simply cannot establish an appropriately sized territory in the aquarium. In the wild, tangs cruise from reef to reef, often swimming impressive distances. These wide distances become a territory that the fish constantly swims in search of algae. Even a very large aquarium has a definitive beginning and end; the fish can only swim so far, before it encounters a wall. Because of this, tangs are unable to form a territory a fraction of the size they are used to traveling in the wild.

This captive stress often translates to a hurdle that must be overcome by the aquarist. It’s not uncommon for some tang species to be reluctant to feed and it’s not uncommon for small juvenile tangs to be harassed, if placed in a tank with larger fish. Because of this, a long quarantine period is required, which allows the fish to spend weeks alone in a tank where it cannot be harassed and special feeding techniques can be employed. Even the quarantine tank must be fairly large, as smaller spaces further upset tangs. This brings us to the common role of the tang police, chasing down aquarists who are keeping tangs in small tanks, usually those between 30-55 gallons. Aquarists with juvenile tangs often don’t understand why a two or three-inch fish wouldn’t be comfortable in such a tank. What’s forgotten is that in the wild, these fish traverse a territory larger than the aquarist’s house and quite possibly larger than the aquarist’s entire property. Suddenly they are relegated to a tiny box with limited space and their natural intuition and nervous system is being over powered by buzzing filters and crammed conditions. It’s this concern that has led some aquarists to believe that keeping tangs in small confines, or multiple species crammed together in one tank, is outright animal abuse.

If a natural aversion to captivity wasn’t enough, all surgeonfish species tend to be susceptible to external parasites. It’s earned them the nickname ich magnets and the reason as to why these fish often become afflicted by parasites is hotly debated. Regardless of the direct cause, it sometimes feels like the more beautiful the tang, the more likely it will become infected with something. This susceptibility demands rigorous quarantine of not only the tang, but any other tank mates added before or after the surgeonfish. Realistically, it’s possible that a fish added before the tang that wasn’t quarantined, could carry a disease that all species within the tank are resistant too. However, it’s quite unlikely the tang will be resistant and even after quarantine, the aquarist is shocked to watch as their tang falls ill.



Many marine aquarists often feed a singular reef blend of food. These are foods that have a mixture of mysis shrimp, fin-fish, squid, etc. For most species, such a blend is a good way to ensure a full bodied nutritional profile. Surgeonfish in the wild are overall herbivorous. In fact, surgeonfish are praised by reef ecologists for their ability to maintain an algae free reef. In the aquarium they require seaweed to be available 24/7. As a grazer, they often pick on food throughout the day and into the night. Using an algae clip and freeze dried seaweed, it’s easy to ensure they have enough greens available.

In captivity however, surgeonfish are true omnivores that will accept a range of meaty foods along with sea weed. This isn’t a problem as it diversifies the fish’s nutritional intake, it’s just vital to ensure that sea weed is also readily available at all times. Surgeonfish’s laterally compressed bodies often make them appear thin and new specimens that have been purged (withheld food for 24-48 hours or more) for shipping often appear almost ghastly. Some aquarists mistake this as the natural appearance of surgeonfish. Surgeonfish, when healthy, are robust fish with a visually rotund belly. A healthy surgeonfish looks more fat than thin.

A diet related challenge can be the fact that not all surgeonfish will readily accept algae from a clip. Over the years, I’ve had multiple specimens that simply ignore an algae clip altogether. Often aquarists assume that sooner or later the fish will get the point of the algae clip, but often specimens will continue ignoring it. A solution is using a rubber band to secure freeze dried seaweed to a piece of live rock. This mimics a more natural feeding scenario and one that most specimens will readily accept. Slowly moving the seaweed, a little each day, toward the aquarium glass and then transitioning to using an algae clip will often adjust a fish to the practice, making feeding much easier for the aquarist.

For many years’ aquarists loaded surgeonfish diets with garlic extracts and additives, believing anecdote that suggests garlic can strengthen the immune system or prevent parasites. Recent study has shown that garlic has no measurable benefit to boosting marine fishes’ immune system and has no anti-parasitic properties. In fact, it’s highly questionable that garlic even stimulates the appetite of marine fish. While it has been shown to treat freshwater piscine parasites when used in high doses diluted in water, it’s not believed to have any effect on fish health when fortified into a food. Relying on garlic infused foods and tinctures to prevent or cure a parasitic outbreak will likely lead to disappointment.

Changing behaviors:

So to re-cap I’ve gone over several attributes of surgeonfish that make them more challenging and demanding than the average marine fish.

  1. They are open water swimmers that require a large territory and plenty of space. Without a large enough space, they will most certainly suffer constant stress.

  2. They are susceptible to both severe captive induced stress and external parasites, including parasites that aren’t effecting other fish within the tank.

  3. They have specialized dietary requirements and need seaweed available at all times.

  4. Often newly purchased specimens are thin and emaciated and may refuse food and can be difficult to adjust to a captive feeding routine.
It’s commonly accepted in the hobby that tangs of the same species cannot be kept together, even in larger than average aquariums. The size of territory an aquarium can provide is so small that a tang will recognize another tang as direct competition for limited resources and do everything to ensure it doesn’t compete for food or space. What many aquarists don’t realize is that tangs (especially certain species) will go after another herbivorous species as well. In tanks under 200 gallons, it’s not uncommon for established tangs to charge both large and dwarf marine angels, or any fish that is herbivorous, including blennies. Some species are notorious for not accepting tank mates at all, and the Sohal tang leads the pack when it comes to constant aggression.

The reality is that many tangs are purchased as small, docile juveniles. Purple tangs are timid and shy when small but grow into confident and belligerent adults. Clown tangs do as well and even the sensitive Achilles tang can eventually become intolerant of other fish. It’s important that aquarists understand that individual tang behavior could have an impact on future stocking decisions.

Tang police:

Often people have a negative opinion of the tang police and feel like anyone who points out an over-stocking concern is being rude, judging the aquarist or jumping to un-warranted conclusions. In actuality, most people who voice such concerns and are overly cautious about stocking density and species are people whom have learned from experience the high cost of keeping species under inappropriate conditions. Stress, lack of desire to feed and disease can quickly down-grade an entire aquarium system, even if one specific species is the only one suffering. Recent scientific experiments have shown that fish aren’t the simple, emotionless animals we once assumed, but are in fact complex, conscious and capable of a full range of emotions. Fish do in fact feel pain in a way which is different but comparable to other animals. Considering the popularity of marine surgeonfish, they are one species that is susceptible to being kept in sub-par conditions and meeting an un-timely demise. It is these concerns that I believe drive the tang police to be so proactive about signaling out aquarists that are keeping tangs in tanks where they don’t belong.

Part of being a successful reef aquarist is having patience and restraint, knowing the limits of your aquarium system and making the best decisions for your long-term success and the well-being of your animals.
About author
Jeremy Gosnell has been a marine aquarist for nearly all his life. While studying sociology in college, Jeremy pursued becoming a professional scuba-diver, eventually serving as a coral reef biology science instructor for the Beautiful Oceans Academy based in Montreal, QB. This took him around the world, exploring some of the planet's incredibly diverse coral reefs.

Also, Jeremy worked on staff at the Pittsburgh Zoo's PBG Aquarium. He has contributed to a variety of aquarium-related publications over a 15 year career including, Freshwater and Marine Aquarium Magazine (FAMA), Aquarium Fish International (AFI), Fish Channel, Tropical Fish Hobbyist Magazine (TFH) and reefs.com. Today, he serves on the content review, editorial board of TFH Magazine in addition to providing original content for online and print publications.

He is also the author of novella Neptune's Garden and novel The Terminal, which won a merit of science fiction award at the 2015 Guadalajara International Book Fair.

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