Powder blue surgeonfish: Look before you keep!


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Tristan Lougher explains why it pays to be prepared before stocking the tricky Powder blue surgeonfish.


Common name: Powder blue tang (surgeonfish).

Scientific name: Acanthurus leucosternon (Ack-ann-thur-uss loo-co-stern-on).

Size: To 23cm/9in.

Origin/natural habitat: Reef flats of the Indian Ocean from the east coast of Africa to Indonesia. Reported also from Bali in the Western Pacific.

Tank size: 400 l/88 gal plus.

Water chemistry: Ammonia and nitrite should be zero. Stable pH 8.1-8.4 is advised. Nitrate should be below 25ppm, ideally lower.

Approximate lifespan: Five years plus. Specimens kept well should live into double figures.

Sexing: External sexual differences have been reported such as nuances in body shape and pattern, but these are not discernible in any but the largest most mature fish where females are substantially larger than males.

Spontaneous purchases of marine fish can work but often don’t. There are so many species to choose from already, and there are several new-to-the-hobby species being imported every year. So, it’s perhaps unsurprising that aquarists can encounter fish they have never seen before in their dealer’s aquaria.

However, there are many fish that are instantly recognisable and about which there is an abundance of information.

Popular because of their ravishing good looks, affordability and widespread availability, one might be forgiven for thinking that they are easy to keep too. While by no means impossible, they can present unprepared aquarists with serious problems. However, a little background research and planning means that an aquarium can be established that provides for the specific needs of these fish in the long-term.

The Powder blue surgeonfish is many things: iconic, beautiful and yet potentially frustrating when it proves difficult to keep. Establishing an aquarium that addresses its particular needs and potential problems from the moment of its conception through to design, construction, then finally stocking is a way of avoiding many of the potential problems with this beautiful surgeonfish. Of course, most Powder blues do not have their entire system designed around them and they can still thrive in mixed systems. However, many aquarists have learned the hard way not to impulse buy one. Most of the key points that help aquarists to achieve success with this species are applicable to any aquarium, but for those wanting to recreate a little slice of nature, the reef flat aquarium is a great place to start.

In common with many surgeonfish, the Powder blue surgeonfish will fiercely defend areas of macroalgae from competitors or indeed any fish it perceives as a threat. In its natural environment, it may have to see off marauding shoals of the rival surgeonfish such as the Convict surgeon, Acanthurus triostegus, with aggressive attacking use of the scalpel-like scales located on its caudal peduncle. Although large shoals numbering hundreds of Powder blue individuals are also seen with regularity, it is generally intolerant of members of its own species and, at the margins of their territories, pairs will display and skirmish with rivals.

Its laterally compressed body shape and low-slung mouth are ideal for getting into nooks and crannies to remove algae, and it will busily swim throughout its territory searching for food. Here it might form loose associations with other species of surgeonfish including members of the genus Ctenochaetus, the bristletooth tangs. It has been suggested that this form of tolerance of similar species is convenient to each, as it increases the chances of new browsing sites being found and also offers some safety in numbers from predators.

Stop problems before they start

Researching potential issues with fish before establishing an aquarium for them allows the aquarist to manage problems before they occur. Aquarists that aspire to maintain the powder blue in the short, medium and long-term must address and solve each of these problems through system design and careful selection.

1. Their tendency to invite disease when stocked into their new home. They invariably contract Cryptocaryon (marine white spot) between two and ten days after being introduced.

2. Specimen selection: Is it feeding? Is it healthy? Of course, these types of questions can and should be asked of any fish before purchase, but for some marine species, identifying those individuals that are bold and greedy in their feeding behaviour can make their transition to the home aquarium an even smoother one.

3. Their territorial nature: many marine fish are territorially aggressive and the Powder blue isn’t the worst of them. It isn’t even the worst surgeonfish, but the same instincts that drive it to defend it’s patch of alga from raiders can kick in in the home aquarium, and in a closed system this can lead to serious injuries being sustained by its tank mates.

Buy better fish

Although research and planning are essential when selecting fish species for inclusion in a saltwater aquarium, it is vitally important that decisions concerning the actual specimen to be stocked into your aquarium are based on the individual rather than the species. Hopefully, you will already have determined whether the species itself is suitable for your particular aquarium, and that includes both hardware and species stocked/to be stocked.

Try to see a number of Powder blue specimens before you buy one. How do they compare with specimens you saw during your research? How do they compare with wild photographed fish?  This should help give you a feel for the species, how it looks in a dealer’s aquarium and some understanding of what to look out for in the individual you end up buying. It is also useful to decide whether a smaller or larger individual is better stocked in your particular circumstance, and that might be influenced by the size and disposition of the other fish to be stocked.

When it comes to the time to buy, ensure that you see it feeding before you commit to the purchase. Ideally, it should browse on algae (dried and/or natural forms) in addition to meaty offerings such as Brine shrimp or Mysis.

Avoid individuals where the spine is visible; it’s possible to reverse the weight loss incurred when fish are collected and shipped and this is likely to occur when fish are fed sufficiently well on quality foodstuffs. However, this is a variable that the new Powder blue owner doesn’t need, and having high standards during the selection process should increase the chances of success.

Occasionally, specimens that are feeding well on flake and pellet diets can be found, and those are likely to be the best settled. Ask how long an individual has been in residence at the dealer’s; the better individuals are likely to have been in stock for a number of days or weeks.

How do we define 'better'? It’s not all about colour although that too can be an indication of health and vitality. Sometimes fish held in intensive marine fish-only systems can lose a little colour over time. The good news is that if the aquarist prioritises the fact that they are feeding well and have recovered from shipping over vibrancy of colour then the intensity and beauty of their colours should be regained within a matter of days in most instances.

Add tank mates first

The benefit of the creation of an aquarium that provides for the needs of fish that can be classed as 'tricky', is that more straightforward species will usually benefit from the extra planning and enhancements to the system. For example, surgeonfish are not the only species to suffer from white spot infections and therefore inclusion of a UV benefits all newly introduced fish. Establishing the aquarium to be sympathetic to the fish’s natural environment could even inspire the aquarist to pursue the biotope aquarium where the sunlit reef flat fauna is recreated to an extent.

The good news is that the Powder blue will live with almost any tank mates given sufficient time to settle in a new home, but its territoriality can be an issue. The willingness to form schools with other, similar algae-grazing species in the wild is not something to be attempted lightly in the aquarium. Indeed, it can be best avoided altogether. Their intolerance of competitors for algae might be understandable, but less easily explained is their apparent hatred of butterflyfish. None of these blends of fish groups are impossible to recreate in the home aquarium but perhaps best avoided in a system where the well-being of the Powder blue is a priority.

Bear in mind that the territorial nature of this surgeonfish is likely to be enhanced by the aquarist offering meagre rations; an approach often adopted by aquarists who understandably want to prioritise their water quality. One of the best ways to avoid conflict is to make this the final large-fish addition to the aquarium, i.e. after all of the other species have been given a chance to settle over a number of weeks. This might not eliminate territoriality entirely, but it should reduce it. That, together with some suitable choices for tank mates can make all the difference.

Another possible solution to the stocking of territorial species is to stock all potentially aggressive species simultaneously and as small juveniles. In the case of most surgeonfish and tangs, which may compete for natural algae resources in the aquarium, there may be limits regarding just how small the specimens available to be stocked are. At least adding them at the same time means that they are all in the position of having been stressed while being moved to their new aquarium and will settle in at similar rates.

This is particularly useful when stocking surgeonfish that are even more territorially aggressive than the Powder blue: surgeonfish such as the Red Sea’s Sohal, Acanthurus sohal, and the Indo-Pacific’s Clown, A. lineatus.

Smaller, busy fish such as anthias (Pseudanthias spp.), damselfish (Pomacentridae), dottybacks (Pseudochromis spp.), fairy wrasse (Cirrhilabrus spp.), peacock wrasse (Macropharyngodon spp.) and flasher wrasse (Paracheilinus spp.) are all suitable groups with which Powder blues will mix with the minimum of conflict. Stock larger fish such as dwarf angelfish, larger wrasse and angelfish before the Powder blue. Of course, any species choices will also be influenced by the variety of sessile invertebrates, if any, that are also stocked.

Good husbandry

For the majority of specimens, once the first month in their new home has been successfully negotiated, they will go from strength to strength. However, water quality must be maintained to high standards and care must be given to the diet of the surgeonfish. Given that the Powder blue is one of the last fish stocked into the system, at least the last fish of any size that should be stocked, attention will have to be given to feeding all of the other fish in the aquarium too and to ensure that they are not competing too strongly with

the Powder blue.

One of the best ways to offer food to this fish is using nori or other forms of dried alga (dried sushi nori is the form I find most Powder blues accept most readily) on a seaweed clip daily. This should ideally be placed into the aquarium in the morning (or when the daylight period of the aquarium begins), so the fish can browse throughout the day. Meatier offerings can be made; pellets and flake are often accepted by this species, as are familiar frozen diets such as

Mysis and Brine shrimp. There are many other formulations of frozen food containing algal enrichments or high percentages of vegetable material that are also suitable. Keep the diet varied and of high quality, but always offer the dried alga.

How to set up a Powder blue surgeonfish tank

Tank size: 400 l/88 gal is an absolute minimum for this species long-term. It will afford swimming space for this active fish and a water volume that is sufficiently large to afford some stability to the system.

Filtration: For me, the best way to create an aquarium sympathetic to the needs of a Powder blue is to make it a living rock based system. This means the bacteria within the rock itself will provide the biological filtration: the removal of ammonia and nitrite.

Nitrate can be controlled to an extent by other varieties of live rock based bacteria and enhanced through the use of carbon dosing, whether with liquid alcohol based products or through the use of bio-pellet reactors. A good-sized, efficient protein skimmer is essential whether carbon dosing is employed or not.

Water currents and their intensity will be determined by the species of coral where stocked, but Powder blues do seem to enjoy areas of vigorous water movement provided by stream-type pumps, as long as  they have areas where they can find quieter water.

Equipment: You are going to need an ultraviolet (UV) steriliser. You might be one of the lucky people who stock a Powder blue that never develops a protozoan parasite such as white spot (Cryptocaryon) or marine velvet (Amyloodinium), but that would place you in the minority of aquarists with experience of this species.

Thinking you might get lucky is a big mistake, and why endanger the life of not only your Powder blue, but also the rest of your stock, as the aforementioned parasites are highly contagious and potentially lethal. This, coupled with the fact that treatment options in a reef aquarium containing live rock and corals are extremely limited and it becomes clear that the UV cannot be seen as an option; it’s compulsory. Prevention is always better than cure in these situations, and running the UV when the fish is introduced to the system and for a period of three to four weeks subsequently will increase your chances of success with this fish.

If you plan on keeping corals in the Powder blue aquarium, and there is no reason why you shouldn’t, then the lighting will need to be adequate for the species/varieties chosen. LED illumination gives that authentic rippling light effect that is such a prominent part of the shallow reef experience. Although the current trend for high percentages of blue light in stony coral aquariums enhances the fluorescent proteins in their tissues, lower Kelvin ratings will afford a whiter light that will showcase the fabulous colouration of the Powder blue as well as faithfully recreate the shallow water in which this fish is commonly encountered.

Aquascaping: Powder blue surgeonfish adore swimming space. In this system, building a shallow incline of reef at about 30 degrees to the horizontal affords plenty of open water and yet still lots of rocky substrate over which the fish can browse for algae. Alternatively, you could opt for a horizontal arrangement of rock with one or two sand or rubble patches that would recreate the reef

flat zone nicely. Corals can be widely spaced giving focal points of interest with plenty of exposed rock over which the fish can browse.

Essential quarantining

Quarantining is a hard process to argue against for any fish, saltwater or freshwater, but reality dictates that few marine aquarists have the budget and space to establish a system into which fish can be placed, observed and treated and therefore don’t own one. Lack of quarantining is another one of the reasons why a UV steriliser is an essential piece of kit for the Powder blue.