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Gobies

Gobies

General characteristics

Behavior

Unusual distinctions

Reproduction and longevity

Resources

Gobies, belonging to the suborder Gobioidei, are small fish that usually live off the coast in tropical and warm temperate regions. They spend the majority of their time resting on the bottom near protective cracks in coral reefs or burrows in the sand. Most species have fused pelvic fins which form a suction cup on their undersides. A goby uses this suction cup to cling to rocks so that it does not wash away with ocean currents.

The suborder of Gobioidei is divided into two to nine families, depending on the taxonomic system employed. The largest family in the suborder, and indeed the largest family of all tropical fishes, is the Gobiidae. Although the count is not complete, there are approximately 212 genera and 1,900 species within the Gobiidae family worldwide; at least 500 of these species live in the Indo-Pacific Ocean.

General characteristics

Although some species are moderately elongated, Gobies are usually very small, compact fish. The smallest vertebrate in the world is, in fact, a goby known as Trimmatom nanus which lives off the Philippine islands. This goby never grows larger than 0.3-0.4 in (8-10 mm) long. Two other gobies living in the Philippinesthe Pandaka pygmaea and the Mistichthys luzonensis are among the shortest freshwater fishes in the world; the females of these species mature at 0.4-0.43 (10-11) mm long. While most of them get no bigger than 4 in (10 cm) long, the largest range up to 19.5 in (50 cm).

One of the most unusual traits of true gobies is the suction cup located on their undersides near their pelvic areas. Their pelvic bones are fused with each other; thus, their pelvic fins are united, at least at the base. In true gobies, the fin is connected by a thin membrane which enables the suction cup to create a vacuum; gobies can use this vacuum to gain a firm hold on objects. This suction cup exists in many different variations. In some species, the pelvic fins are completely connected by a membrane; in others, the fins are partially or completely separated.

Gobies are also characterized by the presence of a two-part dorsal fin, a fin located on their backs. The first part of the dorsal fin can have up to eight unbranched rays, although sometimes these rays are completely absent. Gobies usually, but not always, have some scales; these scales are sometimes present only in specific parts of their bodies. Their mouths are usually located at the very tip of their bodies and often protrude from their faces. Their jaws contain powerful teeth which are well suited for eating invertebrates or small fish.

In general, gobies have developed in quite diverse ways during the course of their evolution. While they usually live in saltwater, they are often found in brackish water, and sometimes even freshwater. In fact, gobies are often the most plentiful fish in freshwater on oceanic islands. A few species even live in rivers in the mountains. They have adapted to live in widely varying habitats, living, for example, inside sponges and even on land.

Behavior

Most goby species are bottom dwellers. Furthermore, they are not very graceful swimmers, because their movements are characteristically jerky. Gobies propel themselves by a few strong beats of their tails and steer themselves with their pectoral fins. They are carnivorous, feeding on crustaceans, small invertebrates, fish eggs, worms, and other small fish.

In most species, the eyes are their most important sensory organ, especially for detecting prey and danger. It should be noted, however, that some species have adapted to living in caves and consequently have no eyes. These species rely primarily on their sense of smell. Also, even in species with normal eyesight, smell is used to recognize members of the opposite sex. Furthermore, gobies have been proven to possess the ability to hear.

Unusual distinctions

Three goby generathe mudskippers (Perioph-thalmus ), the Boleophthalmus, and the Scartelaos act as true amphibians. Perhaps the most well known of these genera is the mudskippers. These gobies can move at considerable speed on land using their armlike pectoral fins. In many species of mudskippers, the pelvic fins are separate and used as independent active arms as well. Interestingly, mudskippers eyes, which are well suited to seeing in air, are located on stalks on the tops of their heads; the fish are able to elevate and retract these stalks depending on their need.

Reproduction and longevity

Gobies breed in the spring and summer. The adult males define a territory around their chosen nests, which are often holes in the rocks, under stones or shells, or even in old shoes. After spawning occurs, the females lay the eggs in a patch on the underside of the nest roof. Male gobies guard the eggs until they hatch.

Depending on the species, gobies can live between one and 12 years. At one extreme, the Aphia and Crystallogobius species die right after their first breeding season when they are one year old. At the other extreme, the rock goby and the leopard-spotted goby do not even mature until they are two years old.

Resources

BOOKS

Nelson, Joseph S. Fishes of the World. 4th ed. New York: John Wiley & Sons, 2006.

Webb, J.E. Guide to Living Fishes. New York: Macmillan, 1991.

Whiteman, Kate. World Encyclopedia of Fish and Shellfish. New York: Lorenz Books, 2000.

Kathryn Snavely

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Gobiidae

Gobiidae (goby; subclass Actinopterygii, order Perciformes) A very large family of coastal-water fish. Most species have the pelvic fins united to form a sucking disc which is used to cling to hard objects on the sea floor. Unlike the clingfish (Gobiesocidae) the gobies have two dorsal fins, the first one being spiny. Gobies form an important part of the fish population of rocky shores, sea-grass beds, and coral reefs. Some species live in close association with other animals, e.g. sea urchins and shrimps. Most gobies are very small; Gobius vittatus (striped goby) of the Mediterranean does not exceed 4 cm. One of the largest gobies is G. giuris of the Indo-Pacific, which reaches a length of 50 cm. With about 800 species, Gobiidae is the largest family of marine fish, found in tropical to temperate waters world-wide.

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