The Lieutenant Surgeonfish (Acanthurus tennentii) is also known as the Doubleband Surgeonfish and Tennents Surgeonfish. Members of the Acanthuridae family have a retractable razor sharp spine on either side of the caudal area. They obtain their name Surgeonfish from these blades. The blades are used for defense and possibly in territorial disputes and can inflict significant damage. The blades are reported to contain toxins but there seems no scientific evidence for this.
The Lieutenant Surgeonfish has an elongated oval body tapering back onto a lunate caudal fin with a laterally compressed body. The head area is rounded and the mouth protrudes slightly. Their body is a light brown colour with black just below the gill plates. However they can change their colouring to dark brown dependant on mood. Behind the gill plate there are two black lines that appear to have been painted on. In front of the eye are two short red lines and the caudal fin is yellow with blue margins. Around the blade in the caudal area is a black spot, lined with blue.There is a blueish tint around the front of the head. They grow up to 30 cm in length but around 25cm is more common in the wild.
LIEUTENANT SURGEONFISH IN THE WILD
The Lieutenant Surgeonfish is not that common overall in Tanzanian coastal waters, but in certain areas in which conditions seem to favor them they can be seen in fairly large numbers. They seem to prefer inshore flat reef structures with plenty of algae on it. They are seen solitary and in groups. Being active fish they are always on the move and feeding.
Lieutenant Surgeonfish are found across the Indo West Pacific area from East Africa to Southern Japan and across to French Polynesia and have been recorded in Hawaii. In Tanzania they are most common around the 5 to 12 meter range on shallow reefs with abundant algal growth and generally some wave action.
The Lieutenant Surgeonfish feed on algae and can be seen feeding in the images, They are quite selective about what they eat and move along a patch of algae until they spot something they like. They obviously have strong preferences in the diet.
Group spawning takes place with the females releasing spawn into the water table and the dominant male fertilizing the eggs. Once the eggs hatch the larvae go through a planktonic stage before settling down.
Lieutenant Surgeonfish are kept in aquariums. They require high quality clean water that is well oxygenated. They are fairly easy to feed but a big part of their diet should be algae in one form or another to keep them healthy. Because of their territorial nature they should not be kept with fish with a similar shape or diet. Great care should be taken when moving them as their blades can easily snag in a net or worst case pierce a bag. Because of their potential size they require a large tank.
Lieutenant Surgeonfish are not commonly caught by fishermen in Tanzania due to their feeding habits and the improbability of taking bait. They are netted or trapped occasionally. In parts of the Pacific they are exploited both for the aquarium trade and as a food source.