This surgeonfish is commonly called the powder blue though the proper name is Acanthurus leucosternon.
The fish is very attractive but should not be found in just any aquarium. For example, it would be wrong and cruel to have one in my reef as the aquarium is too small, and in addition the reef takes up too much of the free seawater space available for swimming making that too small. Many would say the fish should not be kept in an aquarium of less than 5ft (circa 152.5cm) by 2ft (circa 61cm) by 2ft. Subject to the fish load and the available swimming space it could be reasonable to bring the length of the aquarium down to 4ft (circa 122cm). Again the rockwork should leave plenty of swimming space for the fish. There is a further point and that is that in all aquariums the growth potential must be considered. When purchased the fish is likely to be fairly small but, in the wild at least, it has the potential to grow to about 12 inches (circa 30.5cm). It can be seen why larger aquariums are best for this fish.
To keep the fish healthy and happy it is important that seawater is kept at high quality, which is a requirement for any system anyway. Also as in any system, it is important to ensure the seawater is as oxygen rich as possible. This is done by ensuring that seawater movement is optimum so that air/water interfaces are fully efficient.
Only one powder blue should be kept in an aquarium as they could be, and usually are, aggressive and territorial. Further, the fish could take exception to any other surgeon fish present in the aquarium particularly another blue one (of any shade). The fish may even take exception to any other largish blue fish, surgeon or not. It has also been advised that butterflies could be attacked.
So it sounds as if the powder blue is a fish to be avoided. Not really, there are many aquarists who have found keeping one has not caused unfortunate problems. Environment and selection of suitable tank mates is very important, and it could be a good idea to introduce the powder blue to the tank as one of the final additions.
Initial selection of the fish is very important, as it is with all livestock. Time should be taken to ensure the fish is in good health with nothing present that could cause any questions to arise.
Feeding does not present any problems at all. The fish will readily accept the general fare that is offered most other fishes, such as de-frozen food and flake. However, in the wild they feed nearly entirely on algae and so it follows that in captivity algae should be available. In most aquariums the natural algae growth will be insufficient and therefore commercial produce is required. This could be in the form of dried Nori algae, for example, which comes in sheets. The sheet can be reduced in size if necessary and hung in the aquarium on a lettuce clip for the fish to eat. Any uneaten or loose Nori should not be left too long but removed and replaced with fresh. It is likely that if the sheet remains fixed in place it will be eaten, especially if there are other algae eaters present. The aquarist can soon judge the correct amount needed.
There are some marine fish that clearly let the aquarist know how they are feeling by their colouration and the powder blue is one of them. If the fish is a fairly deep blue and the head black then the fish is fine and happy. If the blue has turned pale and the usually black head grayish then the fish is off-colour (sorry, pun not intended! I should have said not well). Check for correct diet and enough of it, seawater quality and any sign of disease. In a high quality environment the fish is reasonably trouble free.
Assuming that the powder blue is not exposed to disease problems and is homed in a suitable situation it adds movement, shape and colour to the aquarist’s collection. Longevity should be good too.
The link provides some pictures of the powder blue, placing the mouse pointer on a picture enlarges it: