Whitecheek Surgeonfish

Photo courtesy from Fishes of Australia

Whitecheek Surgeonfish (Acanthurus nigricans)

Other Names: Whitecheek Tang and Gold-rimmed Surgeonfish
Max. Length: 21.3 centimeters
Length at 1st Maturity: 11.1 centimeters
a value: 0.06700
b value: 2.669
Depth Range: 1 – 67 meters (3 – 220 feet)
Frequency: Abundant in the reefs of the Indo-Pacific Ocean

Photo courtesy from ReefBase

Once believed to thrive only in the Eastern Indian Ocean, scientist hypothesized that a Whitecheek Surgeonfish was able to cross the Pacific Ocean where its population is now flourishing in Cocos Island and neighboring offshore areas.

During your underwater adventures in Cocos island, you will definitely see a whitecheek surgeonfish thriving and taking refuge from branching corals. You can easily identify this small fish through its  purple-blue colored body that has a yellow stripe that runs from the dorsal fins going to the anal fin which looks like a marking from a wishbone. Their pectoral and dorsal fins are highlighted with a blue colored rim while its anal fin has a blue and white color with a vertical yellow lining. But what really stands out in identifying this species is the white markings on its cheek that is located just below the eyes.

Why are they called Surgeonfish?

Photo courtesy from The Pew Charitable Trusts

If you think that they are surgical doctors who operates wounded fish, then you are wrong this time. In fact, it is the other way around. If you try to take a closer look at their tail, you can see that there is a razor-sharp spine that is protruding on both sides of the base of their tail.

This scalpel-like spine can be used both for defense and aggression. If an unlucky fish is hit by the protruding spines of a surgeonfish, it can cause traumatic wounds which can be fatal in some instances. Kidding aside, just imagine if you were the fish being hit by its protruding spine, then you should see a surgeon immediately for a stitch or surgical operation.

Aggressive to itself but not to Others

If you are worried from the premise above, please don’t be. A surgeonfish is only aggressive to its fellow surgeonfish. This is due to the fact that they are highly territorial and that the competition for space and territory between them is relatively high.

But this does not mean that it will not guard its territory from intruders coming from other species. Yes, it will defend its nest especially if eggs and their youngs are being nestled.

Their Food determines their Behavior

Let me point out first that they do not become what they eat. For example: if they eat sharks, then they become one. No, it’s not that way, and only, if they can eat a shark.

What we mean is their behavior can be influenced with the food they eat, if it is meat or a plant since they are an omnivore species. If a surgeonfish consumes more meat than plants, then their behavior becomes more aggressive. If they consume more plants than meat, their behavior becomes more subtle and shy. No wonder why boxing champions and mix martial artists are meat lovers.

But how do we apply this knowledge in our underwater adventures especially in Cocos Island. Use this data and look for indicators. If you see a reef that is teeming with small fish which is considered a potential prey, then expect that the general behavior of surgeonfish in that particular area is aggressive. But if you see a reef that is interspersed with algal growth, then you can expect a subtle and shy surgeonfish.

Reference

Fishbase: www.fishbase.org

IUCN Redlist of Threatened Species: www.iucnredlist.org

Fishes of Australia: www.fishesofaustralia.net.au

Video courtesy from Denis Batalenko

About Tristan Paylado
Tristan is a marine biologist and a CMAS 2-Star Dive Instructor
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