Bulletin 31 - March 1987: The Diversity of Fishes

The Diversity of Fishes

Water covers more than three quarters of the earth’s surface and it is true to say that one can expect to find life in nearly every inch of it. Fish of one kind or another are found in polar seas beneath the ice, in the tropical swamps at the equator, in the greatest depths of the ocean, and at high altitudes in hill streams. Due to the varying nature of their environment, fish have evolved into a number of different forms and this has provided us with a staggering 22 000 different species. Our own Gulf waters are home to over 200 species that vary in distribution, population and even coloration between the Gulf of Oman in the east and the Arabian Gulf to the west.

All fish are classified according to their family, genus and species and it is the latter two elements that combine to form the scientific (Latin) name. Although common names are applied to every species, because of language difficulties, scientific names are normally used for precise identification.

Few things are more dazzling of bewildering on one’s first expedition to the undersea world than the overwhelming variety of fishes. How, then, does one set about identifying them when there are so many different types. Even differences, which may appear obvious underwater, often prove very difficult to pin down once back on dry land. The best approach for the beginner is to try to recognize whether a particular fish is a member of one of the larger families because, in fact, the great majority does belong to quite a small number of families. The fish in each family tend to have their own characteristic shape and, once this is recognized, the different species can be distinguished by their individual coloration and markings.

These range from the huge Hump-headed wrasse (Cheilinus undulates), which grows to two meters in length and can weigh up to 90 kilograms, to the tiny cleaner wrasse (Labroides dimidiatus) which spends its life cleaning parasites from the bodies and mouths of any fishes which arrive at the wrasse’s designated cleaning station.

Parrotfishes are perhaps the most easily recognizable family because they have clearly discernible bird-like beaks that they use to scrape the algae, on which they feed, from the surface of rocks and coral.The precise identification of individuals is often quite difficult because the male and female of the same species can be completely different in color and have different markings.

These fishes are among the best known species because of their attractive shape and coloration. They are all very flattened from side to side and have a basic disc-like shape.

This family is probably the largest in terms of sheer numbers and contains the most common fish in Abu Dhabi waters – the so-called Sergeant major (Abudefduf saxatilis), conspicuous because of its black and yellow vertical banding.

These two families contribute significantly to the catches of local fishermen, as a visit to any of the country’s fish souks will attest. Both are predators on medium-sized invertebrates such as shrimps, crabs and large worms.

Another approach is to associate fish with their habits, for example nocturnal feeders. This group will include the squirrel and soldier fishes (family Holocentridae). By day they will be seen resting near the entrance of their holes or caves almost as if they were on guard, but at night they roam freely feeding on shrimps and small crabs. Also included in this category are the lionfishes (family Synanceiidae), which are probably the stealthiest hunters of the sea.

All nocturnal fish are characterized by their red coloration and large eyes, an obvious adaptation. At night, under natural conditions, the red coloration appears black thus rending the fish inconspicuous.

The last group to be considered is the so-called fish-eating predators. It includes fish both large and small, from the Hammerhead shark (Sphyrna lewini) at one extreme to the tiny hawkfish (Paracirrhites fosteri) at the other.

No study of Gulf fishes would be complete without mention of the groupers (family Serranidae), known locally as Hamour, which have come to be recognized as one of the tastiest fish available anywhere in the world.