RSS Survival on the reef part 3: Distractions and decoys

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  1. MASA Admin

    MASA Admin Moderator

    8 May 2007
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    Continuing with our mini series on reef fish survival techniques, we stray away from mimicry and take a look at how some fishes use the art of distraction to fool their predators. Not everyone has the ability to conceal their body to look like a floating piece of leaf, nor have they the ability to copy poisonous or venomous models. In such fishes a decoy is usually necessary to prevent death, or at least minimise injuries and increase chances of survival. Chelmon rostratus above has a large false eye called an ocelli on its dorsal fin. This is a predatory distraction technique employed by many organisms, and in this last edition of our three part series, we take a special look at some of these examples. 

    [​IMG]A Ypthima butterfly distracts predators with the large eye spot on its wings.

    Using distraction as a form of protection has been around for thousands of years. In the insect kingdom this trick is well mastered by numerous species spanning multiple families. Certain species of praying mantis when startled can fan their wings to reveal a hidden eye spot to distract predators, allowing a grace period for a quick escape. Many butterflies such as this Ypthima horsfieldii have false eyes on the wings. Lizards or birds looking for a quick meal may get distracted by the false eyes, which draws the attacker away from their head and body. At best the insect escapes with a broken wing to live another day.

    Some species of butterflies are remarkable in having tails and pendulous lobes on their hind wings. These tails and lobes mimic the antennae and eyes, and makes for a remarkable distraction. This increases the likelihood of a predator aiming at the wrong end, and in return all it gets is a mouthful of wing, which is not crucial for the survival of the insect. While this may not be a hundred percent, the occurrence of many individuals with broken wings corresponding to placement of these decoys suggests that it works.

    [​IMG]Chaetodon auriga with ocelli on soft dorsal fin. Photo by Okinawa-zukan.

    Like terrestrial butterflies, many species of fish, especially butterflyfish adopt false eyes at the rear end of their bodies. This placement of the spot near the tail end helps distract predators away from the real eye and head. Some species only possess an ocelli at their juvenile stage, and lose it as they grow older. As juveniles are vulnerable and make for easy target, the possession of a false eye may be a life saver. As they grow into their adult form and are more capable of fleeing from predators, some species lose their ocelli. Chaetodon lunula, C. assarius, C. dolosus and C. marleyi are some of many examples whose juveniles possess eyespots while the adults don’t.

    In an unfortunate event of predation, the butterflyfish may escape with a missing tail or a good portion of the dorsal fin which will heal over in time. Although this may severely handicap the fish, it may not be life threatening. Many examples of fish with missing tails or even a chunk of their bodies eaten off have been observed to live in the reef, seemingly unaffected. Although their swimming and manoeuvring may be compromised, at least they get to carry on living and procreate.

    [​IMG]A pair of Chaetodon capistratus with missing portions of their dorsal fin. Photo from

    In the pair of Chaetodon capistratus above, both specimens have visible damage on their dorsal fins. It is not uncommon to find such instances where predatory fish attack the wrong end due to the positioning of the false eye. In this case, the butterflyfish manages to escape with a missing portion of its fin. Because the injury is deep within the spinal portion, it will not grow back completely but has healed over instead. This is one of the better scenarios, and in severe instances, a tail or larger portion of the fin may be removed.

    [​IMG]Chaetodon falcula has a disruptive eye band as well as a peduncle stripe. Photo from

    While not all butterflyfish have ocelli, a very large majority have disruptive eye stripes. Many species of fish, and in this case butterflyfish, make use of disruptive eye stripes to conceal their real eye. It is also not uncommon to find an additional band or stripe on the caudal peduncle on the opposite end, like C. falcula above. This can make both ends of the fish symmetrical and differentiating the head portion would be trickier for predators.

    [​IMG]Chaetodon unimaculatus surviving a near fatal injury. Could be due to that eye spot.

    Many species like Chaetodon auriga make use of both a disruptive eye stripe and false ocelli for double the effect. The concealment of the eye is not restricted to just butterflyfish. As the head and especially the eye is a highly vital and essential organ, many species make an effort in concealing it. Eye-stripes aside, different types of patterns such as masks can also be employed to conceal the ocular region. Chaetodon adiergastos, C. semilarvatus and C. lunula for example all use large and dark masks to conceal the eye.

    [​IMG]Two species of butterflyfish adopting disruptive eye stripes with missing tails. Photo from Pacific Island Aquatics and Hong Kong Sealife.

    The photo above shows a tailless Chaetodon multicinctus and C. falcula. Both these species adopt a disruptive eye stripe as well as a corresponding band on their caudal peduncle. It is quite possible that these were victims of a predatory attack, in which the offending fish bit at the wrong end resulting in the evisceration of the tail. While swimming may not be as agile, a fish can lead a perfectly normal life without a tail. An addition band and the concealment of the eye in this case, goes a long way.

    [​IMG]Heniochus chrysostomus adopts a banded pattern to disrupt its body outline. Photo by

    Another technique for distracting a predator is the disruption of body outlines. In many reef species, taking on a dichromatic banded appearance can help break up the silhouette of the fish. Like a tiger with its vertical stripes, fishes with disruptive banding patterns can set out to conceal themselves. A banded contrasting pattern can also help a fish blend in with its surroundings, especially in dimly lit areas with shadows.

    Many species of Dascyllus damsels as well as Heniochus butterflies for example adopt this body disrupting coloration. In H. chrysostomus above, the bands not only help to break up the silhouette of the fish in its environment, it also helps to conceal its eye. In a group, banded disruptive body patterning is especially useful in confusing and disorienting a predator. Much like how a herd of zebra stay close together. Many Heniochus also have long filamentous banners that arise from their dorsal spine. This helps to break up the normal fish shape even more and the trailing filaments could help in predator distraction. It is not uncommon to find fishes with missing streamers.

    In summary, we’ve seen how various fishes adapt to live on the reefs in relative safety. It is a risky environment fraught with danger, and everyday alive is a blessing for these vulnerable fish. We’ve seen how certain fish masquerade under false colours by mimicking their models, as well as staying incognito under camouflage. Finally in this article we explore the use of disruptive coloration as well as distracting eye spots that many species use in a last ditch attempt at survival. We hope you’ve found this series useful and the next time you look at your aquarium fish, know that it took a lot for him to survive. Now that it’s in your care, it is your responsibility to treat it well!
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