Damselfish and their Manly Habits in Cocos Island

While drifting over the reefs of Cocos island, you will notice that there are a variety of small-sized fish thriving near the bottom of the reef floor. Although dominantly composed of brightly colored fish, the species of damselfish that you will find in Cocos island are not that brightly colored as compared to the ones you will find in tropical Asian dive sites. But what will interest you, if you have the opportunity for a close interaction, is their behavior rather than body coloration.

Highly Territorial

If you take a closer look at the habitat of a damselfish, you will notice that they are considering corals and rocky crevices as their home where they build their den. Males seldom leave their den and if there is a need to go out of their comfort zone to feed, they go upwards to do the so-called vertical feeding. They eat microscopic animals that can be found just above its den rather than roaming around horizontally along the reef as what most predators do.

Males compete for territory where an individual with a bigger size often gets the best spot. Territory is very important especially for male damselfish. Aside from having their own and private space where they are willing to defend it against fellow damselfish intruders, females are highly welcome to visit a male territory during spawning season.

Although it is very hard to determine the sex of a damselfish, they can easily be determined during spawning season just by looking at their behavior. On the onset of this annual event triggered by environmental factors, males get highly excited but still highly territorial and never leaves its den. While female damselfish wander the reef to find a mate, males invite them to visit their territory by performing the courtship dance. Males accomplish the dance by going out of its den and make a sudden ascent. While hovering above its den in mid-water, males do a jerky movement to attract females. To further guide the female, males may go in and out of its den repeatedly to signal that this is the place to be in making their next generation.

Major Species of Damselfish in Cocos Island

Panamic Sergeant Major (Abudefduf troschelii)

Other name: Pacific Sergeant Major
Max. Length: 20 centimeters
Length at 1st Maturity: 12.9 centimeters
a value:
b value:
Depth Range: 1 – 12 meters (3 – 40 feet)
Frequency: Abundant in the reefs of the Eastern Pacific Ocean

Due to its size, the Panamic Sergeant Major is one of the species of damselfish that do not  take refuge in the calcareous branches of a coral. Instead, when you diving in Cocos island, you will see them under rocky crevices that has a top and side entry.

Similar to a barberfish, a Panamic Sergeant Major has a duty to perform. But not on a Military-type of duty where their name is derive as the five black bars on the side of its body has a close resemblance to a rank Insignia of an Active Officer on duty. Rather, it has something to do with cleaning other fish. Their cleaning duties has nothing to do with sharks where they are known to serve mullets, halfbeaks and needlefish. Their work station are known to be secondary cleaning station that is mostly located in the middle of the reef flat instead of the traditional ledges of the reef.

Scissortail Damselfish (Chromis atrilobata)

Max. Length: 13.4 centimeters
Length at 1st Maturity: 9.1 centimeters
a value: 0.00523
b value: 3.416
Depth Range: 6 – 80 meters (20 – 250 feet)
Frequency: Abundant in the reefs of the Eastern Pacific Ocean

We can say that a scissortail damselfish is an open-minded fish on the basis on how they secure their territory. Especially for males, the territorial space for a scissortail damselfish may only require a relatively small space where you can see them in Cocos island closely living with each other. This is the reason why they have a huge population where they can easily replenish their loss in numbers due to predation.

But what do their name suggest? Is their caudal fins as sharp as a pair of scissors? No, they’re not. In fact they are very smooth. Their name was derived from the two slanting black lines at their caudal tail, which, if you compare it to a barber’s tool, looks like a pair of scissors.

Giant Damselfish (Microspathdon dorsalis)

Max. Length: 31 centimeters
Length at 1st Maturity: 19 centimeters
a value:
b value:
Depth Range: 1 – 5 meters (3 – 15 feet)
Frequency: Abundant in the reefs of the Eastern Pacific Ocean

As their name suggest, this particular species is considered as the biggest specimen of damselfish you will ever see in Cocos island. Measuring over a third of a meter, a giant damselfish has a close resemblance to a snapper rather than to its close kin in the damselfish family of Pomacentridae.

When you go diving in Cocos island and start descending to the reef floor, a giant damselfish is one of the first greeters that welcomes your presence underwater. Instead of thriving in deep water, they prefer to inhabit the shallow waters with rocky structures. While there are other shallow-dwelling species in Cocos island, you will never miss identifying a giant damselfish through its robust body that is usually colored dark grey or blue-black. This is on top of the lime blue or green line that traverses along its dorsal and caudal fin.

Southern Whitetail Major (Stegastes beebei)

Other name: Ringtail Damselfish
Max. Length: 15 centimeters
Length at 1st Maturity: 10 centimeters
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Depth Range: 1 – 5 meters (3 – 15 feet)
Frequency: Abundant in the reefs of the Eastern Pacific Ocean

Along with the giant damselfish, a Southern Whitetail Major is another species of damselfish that welcomes your presence as you begin your underwater adventures in Cocos island. But contrary to giant damselfish, the Southern Whitetail Major is small in terms of size and prefers to take refuge in tiny cracks and narrow holes that is just enough to fit for itself.

Similar to a giant damselfish, a Southern Whitetail Major is dull-colored where they mostly have a dark-brown body. Its main identifying mark is the white dash of shade that circles around the base of its tail.

Beaubrummel (Stegastes flavilatus)

Max. Length: 10 centimeters
Length at 1st Maturity: 7 centimeters
a value:
b value:
Depth Range: 1 – 10  meters (3 – 30  feet)
Frequency: Abundant in the reefs of the Eastern Pacific Ocean

Opposite to the behavior of a scissortail damselfish, the Beaubrummel is a highly territorial damselfish. As long as there is not much difference in size, it will try to defend its territory against fellow damselfish intruders. It may aggressively guard its rocky-crevice den even if the intruder is slightly bigger.

The Beaubrummel is one of the brightly colored damselfish you can see in Cocos island. Although considered as a relatively small fish, you will be attracted with its dual-colored body mostly composed of blue on the upper portion and yellow on the lower portion. They also have a black colored pseudo-eye that is highlighted with a streak of neon blue on its circumference.

Males do the Childcare

Unlike humans, male damselfish in general takes care of raising their offspring alone where the female leaves after spawning. Starting from the very moment where the fertilized eggs are laid down inside its den, male damselfish further develops their manly behavior by guarding the nest.

While their fertilized eggs needs tendering and their mother is not around, male damselfish takes the dual role of a mother and a father. Male damselfish constantly watch the eggs for any sediment intrusion and supply maximum aeration by continuously swimming in a circular motion around the nest.

On a serious note to reflect, this could be the basis on the story plot of a box-office computer animated movie featuring an orange-colored damselfish with a prominent white slanting stripes, also called as the clownfish. You can see in the movie that the father clownfish took care of its fertilized eggs until a predator wiped-out its offspring with only a lone survivor. But wait a minute, this species is not mentioned in the above list of damselfish. Does this mean that the search for Nemo continues in Cocos island?

Reference

Fishbase: www.fishbase.org

Wikipedia: www.wikipedia.org

IMDb: www.imdb.com

Video courtesy from pv2607