Family Gobiidae
gobies and true gobies

Currently 212 genera and 1,875 species are recognized, making gobies the largest marine fish family and the most species-rich family of vertebrates. Gobies and blennies combined make up a dominant portion of the small fish inhabiting benthic tropical reefs around the world. Additionally, gobies are usually the most abundant freshwater fish on oceanic islands. This group is so poorly known due to their cryptic and secretive nature that 10 to 20 new species are described each year, making them the marine family with the greatest number of newly described species. The range of morphology, behavior, habitat and reproductive strategies within this family is undeniably impressive. (Hoese, 1998; Nelson, 1994; Thresher, 1984)

Gobies are found worldwide in fresh, brackish and saltwater. They are concentrated in the tropics and subtropics, mainly of the Indo-Pacific, but some marine species can be found in the subarctic streams of southern Siberia. Gobies have been transported beyond their natural range via the intake pipes or ballast water of large ships. One species, Neogobius melanostomus, a native of the Black and Caspian Seas, was introduced into one of the Great Lakes in North America around 1990 and has since spread into all five. Between 1960 and 1963 two marine gobies native to Japan, Korea, and China had established populations along the California coastline and by 1980 they were established in several parts of Australia. (Berra, 2001; Hoese, 1998)

Gobies are extremely successful in their ability to exploit microhabitats inaccessible to most other fishes; they are found from subarctic streams in Siberia to mountain streams at altitudes of 2,000 m on islands to ocean depths of 800 m. On coral reefs, they can be found in the numerous cracks and crevices or out in the open among corals (Gobiosoma). Others build burrows (Signigobius) or use the burrows of invertebrates, ranging from polychaete worms to clams. Members of the genera Boleophthalmus, Periophthalmus, Periophthalmadon, Scartelaos, and Bathygobius have uniquely adapted to tidepools, mudflats and mangrove swamps, where some even climb out of the water for extended periods to forage (discussed further in Food Habits). Still others build numerous holes along sandy beaches (Coryphopterus) or compose a large part of the fishes in estuaries, inland seas and continental shelf environments as deep as 800 m. (Böhlke and Chaplin, 1994; Hoese, 1998; Moyle and Cech, 2000)

The approximately 200 species found in freshwater form a separate category of gobies. Gobies are extremely successful in freshwater habitats where few other fish are found, such as oceanic islands. Half of the freshwater species are part of the subfamily Sicydiinae. Members of this group exhibit a high degree of island endemism and some even reach the headwaters of high-elevation rivers (2,000 m) in mountains. Some species have a short marine life-stage while others have evolved to live completely within freshwater environments. (Berra, 2001; Böhlke and Chaplin, 1994; Hoese, 1998; Nelson, 1994)

As might be expected in such a large family, there is some controversy over the classification of gobies. Recently, the eleotrid-like forms within the Gobiodei were named as a separate family, the Eleotridae. If one were to include eleotrids, as some authors recommend (Hoese and Gill, 1993), the gobies would rival the cyprinids as the largest fish family in the world. Hoese (1984) and Birdsong et al. (1988) recognize four subfamilies of the Gobiidae and Pezold (1993) adds one more. The five currently recognized subfamilies are Oxudercinae, Amblyopinae, Sicydiinae, Gobionellinae, and Gobiinae. (Berra, 2001)

Most gobies are extremely small; in fact, the smallest known vertebrate is a goby from Japan, no longer than 10 mm at sexual maturity. The largest, Gobioides broussenetii from the Caribbean, may reach 50 cm TL. Gobies are usually recognized by their small size, the existence of two dorsal fins (the first with eight flexible spines and the second soft), and a blunt round head with large eyes. Some gobies have prominent head barbells as well. Most gobies, and all freshwater species, have pelvic fins united to form an adhesive or sucking disc. However, some reef species have separated pelvic fins although the degree of separation is highly variable. The scales may be cycloid, ctenoid, or absent and the lateral line is absent. (Click here to see a fish diagram). (Berra, 2001; Moyle and Cech, 2000; Nelson, 1994)

Coloration in gobies ranges from vivid, especially in reef species like the brilliantly marked neon gobies, to drab, as in many estuarine species (Bathygobius). Still others may be pallid or translucent (Coryphopterus). Although most reef gobies are sexually monomorphic in terms of permanent coloration and gross morphology, temporary sexual dichromatism (color differences between the sexes) has been observed during courtship and spawning on reefs and other habitats. When permanent sexual dimorphism does occur, it may vary even within a genus. For instance, males in some genera, Lythrypnus and Coryphopterus, have longer dorsal and/or anal spines than females, but other species within these genera lack any morphological differences. Permanent sexual dichromatism also exists in some species but investigators have been unable to explain why there is such variation within genera. (Böhlke and Chaplin, 1994; Hoese and Moore, 1998; Thresher, 1984)

Many gobies have evolved unique physical adaptations for life in tidal or estuarine environments. For instance, mudskippers, which span the genera Boleophthalmus, Periophthalmus, Periophthalmadon, and Scartelaos, are essentially amphibious. The skin contains numerous blood vessels enabling them to take up atmospheric oxygen and a muscular tail helps them to skip over the mud. Additionally, their eyes are perched high on the head to allow them to forage effectively and avoid predation. Another goby, Gillichthys mirabilis, has evolved a highly vascularized buccopharynx, which allows it to gulp air from the surface when the waters it inhabits become depleted of oxygen. (Berra, 2001; Hoese, 1998)

In most gobies, eggs hatch in one to five days and grow rapidly within a few days. At hatching the larvae are quite advanced with pigmented eyes, well-developed jaws, digestive tracts, and vertical fin folds. The small transparent larvae (between 2 and 10 mm long) are usually dispersed in the water column where they swim for three to 20 days. Finally, the larvae settle into a suitable habitat and develop colors that allow them to blend in with the surroundings. They reach sexual maturity within a few months. However, in temperate climates development may take much longer, with sexual maturity occurring after one to two years. (Hoese, 1998)

A notable exception to this developmental pattern (and there are likely many others) can be found in burrowing gobies. In this species, the male remains in a burrow, which is sealed shut by the female, for up to five days. During this time, the burrow is periodically reopened and the eggs cleaned by both male and female before the male is again sealed in the burrow. The eggs develop entirely within the burrow and only one juvenile apparently exits the burrow, suggesting that juveniles receive nourishment through cannibalism, as well as food reserves and their surroundings. Upon exiting, the juvenile immediately begins a benthic existence. (Thresher, 1984)

Tropical gobies develop very quickly and probably live no longer than one year but in cooler areas some species may live between two and ten years. (Hoese, 1998)

Nearly all gobies are benthic (bottom-dwelling) but in some groups (Iglossus, Nemateleotris) individuals hover just above the bottom, seldom moving very far from shelter. Many male gobies are extremely aggressive towards invading males but exhibit a much more relaxed behavior in response to females entering their territory. Pheromones are thought to play a pivotal role in this recognition. The various forms of social hierarchies found in gobies are discussed in Reproduction above. Some gobies engage in symbiotic relationships with sponges, branched corals, or other fishes in the form of cleaners Gobiosoma. However, other apparently symbiotic relationships are better described as parasitic. For instance, gobies that use sea urchins as cover have been observed feeding on the urchins’ tube feet. (Berra, 2001; Moyle and Cech, 2000; Thresher, 1984)

There is considerable evidence that gobies use visual, tactile, chemical, auditory, or olfactory cues in reproduction and territorial behavior (see Reproduction and Behavior). It is quite likely that investigators will find more evidence of different types of communication as research progresses. (Moyle and Cech, 2000; Thresher, 1984)

Gobies are classified as zooplanktivores, omnivores, and carnivores, as they feed on a wide variety of small organisms like crabs, shrimps, smaller crustaceans (such as copepods, amphipods, and ostracods), mollusks, annelids, polychaetes, formaninferans, sponges, small fishes, and eggs of various invertebrates and fishes. Many gobies are quite selective in their feeding habits, favoring an individual prey item, such as a minute algae or small invertebrate. Others have evolved unusual adaptations to allowing feeding in habitats formerly off-limits to fish. For instance, mudskippers (Boleophthalmus, Periophthalmus, Periophthalmadon, and Scartelaos) take on an amphibious character, actively foraging over mudflats and up mangrove roots for crustaceans and insects (see Physical Description for more information on this). Members of the genus Gobiosoma are well known for their brilliant colors used to distinguish them as cleaner fishes. These gobies feed on the parasites and dead skin of larger fish. Some freshwater species of the subfamily Sicydiinae are amphidromous: the larvae are carried downstream to the ocean where they feed and grow (they travel for feeding, not reproduction, unlike many other fishes) before migrating back to freshwater island habitats. (Allen and Robertson, 1994; Berra, 2001; Harmelin-Vivien, 2002)

Due to their small size, gobies must be wary of many different predators, such as sea snakes, shore birds and larger fishes. It’s no surprise that they have developed a wide range of behaviors to defend themselves. Perhaps the most characteristic feature of gobies is their secretive nature. They rarely leave their burrows and display a wide range of coloration for camouflage. Some gobies are translucent and have only a few colored spots to match their surroundings while others have formed symbiotic relationships with shrimp. In the latter case Crytocentrus steinitzni sits outside the burrow watching guard while the shrimp clears out the burrow they share. Cleaner fishes of the genus Gobiosoma enjoy relative freedom from predation due to their color pattern and cleaning behavior. Others live within sponges, sea urchins, the branches of corals, or the roofs of caves for protection. Some gobies even rely on chemical protection, producing a poison called tetrodotoxin, which also occurs in pufferfishes and species of salamander. Some morphological adaptations can be found in mudskippers (Boleophthalmus, Periophthalmus, Periophthalmadon, and Scartelaos). The eyes of mudskippers are located on the tops of their heads to detect and avoid shore birds as well as to locate prey, and their powerful tail allows them to move quickly along the mud. (Böhlke and Chaplin, 1994; Helfman, Collete, and Facey, 1997; Hoese, 1998)

Gobies are extremely important in almost any ecosystem they occupy because their relative abundance makes them an essential part of the food chain. Gobies have the greatest impact on the benthic environment since most reside there. Gobies may be the keystone species (dominant in the food chain) in the freshwaters of small oceanic islands because they are often one of the few species of fish that exist in these areas. (Allen and Robertson, 1994; Helfman, Collete, and Facey, 1997)

No specific information was found concerning any negative impacts to humans.

In the Caribbean and Philippines amphidromous gobies (see Food Habits) form a large portion of the catch as they migrate upstream in freshwater creeks. A number of gobies have been successfully bred in captivity, and some are also popular in the aquarium trade. (Allen and Robertson, 1994; Hoese, 1998)

There are five critically endangered gobies, 18 listed as vulnerable, and 12 listed as low risk. Agricultural practices and the introduction of non-native species are some important causes for their decline. This is not surprising considering the diversity of this family and the fact that many are confined to a single lake or river system, or one or few islands. Some may go extinct before humans become aware of their existence. (Hoese, 1998; The World Conservation Union, 2002)