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Why Are Our Fish So Colourful?

AngelfishThis question must have been asked by thousands of snorkellers and divers as they emerge from their watery adventure. Studies of butterfly fish have shown that species found in temperate waters tend to have simpler patterns and duller colours than those found on coral reefs. Since there are fewer species in these regions, this suggests that the primary function of colours and patterns is species recognition. In a situation where so many different fish intermingle it is vital for each individual to be able to identify a mate easily.

It has also been suggested that in an environment as colourful as the Great Barrier Reef, patterns and colours act as camouflage. Certainly it can be surprising how well a bright fish disappears against a background of coral, sponge or algae. However some fish are so strongly marked as to suggest another function for their colours.

Anemone Fish It is likely that the reasons for colours and patterns are almost as varied as the fish themselves. However, when discussing the significance of fish colours (and indeed animal behaviour) we must be very careful. Convincing as many of the explanations put forwards seem, we must bear in mind that we cannot avoid our human perspective.

Although it is believed that many fish can see colours and that they do have good vision, we can never be really sure what they see. It is possible that colours and patterns have no meaning or function whatsoever. They may be entirely incidental (inherited along with a gene which also passed on a truly useful attribute and enabled that species to survive the tough world of underwater selection). However, the theories are worth consideration and, who knows, our anthropomorphic interpretation may be correct.

Coral Trout Baby Clothes: Some juvenile fish are so dramatically different from adult forms that for a long time they were assumed to be a different species. The patterns of some juvenile may make the smaller and more vulnerable fish less visible to predators. The difference may also prevent adult fish wasting energies on either courting or defending territories against irrelevant juveniles.

Pyjamas: At night some fish hide away in cracks and caves and many can make themselves even less conspicuous by deliberately making their flashy colours duller. This is common in butterfly fish.

Lyretail Trickery: Most fish must constantly guard against being eaten. Some confuse predators by concealing their eye with a black line and some also have a false eye spot on the dorsal fin. (Eye spots are quite common in juvenile fish). This may fool predators into attacking the wrong end of the fish. When attacked, if the butterfly fish does not escape entirely by swimming off in an unexpected direction, it will lose just a mouthful of fin instead of its head! Like many fish the strong patterns on its body may break up it's outline and make it more difficult to spot.

Sex Ads: A number of reef fish have different colours according to whether they are male or female. In a world where sex changes are the norm, this could be an important way of letting prospective mates know that although you were a female last week you are now a male!

Pufferfish Warnings: Many poisonous fish are very brightly coloured and patterned and it is assumed that this warns potential predators that they are not good to eat.

Mood Changes: Changing colour with mood is common. Some fish are known to develop stronger colours prior to spawning. The cleaner wrasse may induce a relaxed state over the fish in which it is attached to therefore colours may be more relaxed. When fish become bossy and protective there colours become more vibrant.

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Diving Cairns - Cairns, Queensland 4870 Australia | Phone: (07) 4041 7536 | E-mail:
Diving Cairns - The ultimate guide to a diving holiday on North Queensland's Great Barrier Reef