Eleotrids (except, presumably, for one eyeless species, Milyeringa veritas) recognize food and potential mates by sight. During breeding season males of some species change color, providing a visual message to potential mates and competitors. Other modes of communication likely exist, but no information was found regarding these or non-visual perception channels.
Communication Channels: visual
Perception Channels: visual ; tactile ; chemical
Based on information gathered in 1994, 16 species within Eleotridae are near threatened or vulnerable. Their populations are either small in terms of adult individuals or in terms of total area in which they are found, rendering them vulnerable to human exploitation, pollution, hybridization, competitors, parasites, or disease.
Many freshwater eleotrids are amphidromous: after hatching they float downstream to brackish or marine waters where they pass through a planktonic larval stage, growing and feeding for a few months before they migrate back to fresh water as juveniles. This marine stage is thought to indicate that Eleotridae originated as a marine family. Some freshwater gobies develop without a planktonic larval stage, becoming a benthic juvenile directly after hatching, and this may be the case for some eleotrids as well.
The family Eleotridae contains about 35 genera and 150 species, and of these most are found in the tropical Indo-Pacific. They are commonly known as sleepers, or gudgeons in Australia and New Guinea, and in New Zealand they are called bullies. The family is similar to Gobiidae but generally lacks the pelvic fin fusion that creates a “sucking disc” in gobies. The majority of eleotrids lives in brackish or fresh water. Only a few species are truly marine, but many fresh water species have a marine larval stage and return inland as juveniles. They are carnivorous, and in turn are eaten by humans in many parts of their range. Sixteen species of eleotrids are listed as near threatened or vulnerable to extinction.
No specific information was found concerning any negative impacts to humans.
Eleotrids are used for food in many regions. The freshwater species Dormitator maculates (fat sleeper) is considered a delicacy in Thailand, Sumatra, Borneo, and the Malay Peninsula. Eleotrids are easy to breed in captivity and are used as aquarium fish.
Positive Impacts: pet trade ; food
Often the major predators in island stream systems, eleotrids form an important element of the freshwater fauna in the regions in which they are found. Many impact not only the crustaceans, fishes, and insects on which they feed as adults, but also join the marine planktonic ecosystem as larvae. Eleotrids are able to occupy various habitats, including brackish and hypoxic (low-oxygen) areas.
Eleotrids are carnivores that feed on crustaceans and other benthic invertebrates, small fishes, and insects. Many species pass through a marine larval stage during which they feed on plankton.
Primary Diet: carnivore (Piscivore , Insectivore , Eats non-insect arthropods)
Eleotrids can be found worldwide between the 40th parallels (tropical and subtropical regions), reaching farther south in New Zealand. They occur on five continents and are common in the islands of the Indo-Pacific.
Biogeographic Regions: nearctic (Native ); palearctic (Native ); oriental (Native ); ethiopian (Native ); neotropical (Native ); australian (Native ); oceanic islands (Native ); indian ocean (Native ); pacific ocean (Native ); mediterranean sea (Native )
Other Geographic Terms: island endemic
Eleotrids occupy mostly fresh and brackish water. While only a few species are marine, many freshwater eleotrids spend their larval stage in the ocean and return inland as juveniles. They live in tropical and subtropical areas, and a few occur in warm temperate waters. They are common residents of mangrove and other estuarine environments. Eleotrids can be found near rocky reefs in bays, in intertidal areas, and in streams or ponds. Some prefer still water among aquatic vegetation. Many live on muddy substrates (bottoms)—most eleotrids are benthic (bottom-dwelling)—but a few are free-swimming.
Habitat Regions: temperate ; tropical ; saltwater or marine ; freshwater
Aquatic Biomes: benthic ; reef ; lakes and ponds; rivers and streams; coastal ; brackish water
Other Habitat Features: estuarine ; intertidal or littoral
No information was found regarding the lifespan in Eleotridae. However, some small gobies (similar in many respects to eleotrids) may mature quickly and live only one or two years.
Eleotrids are small, most measuring between three and 20 cm, although one species, Oxyeleotris marmorata, reaches 66 cm. They are similar to members of the family Gobiidae, with similar head shape, an elongate body, no lateral line, and two separate dorsal fins. They are generally distinguished from Gobiidae on the basis of their separated pelvic fins that do not form a sucking disc. The degree of pelvic fin separation varies, however, and cannot reliably be the only characteristic used to identify eleotrids. Eleotrids can have cycloid or ctenoid (rough-edged) scales. They lack sensory pores, and have canals only on the head. Their mouths, filled with several rows of conical teeth, can be upturned or terminal, but never inferior. The first dorsal fin contains two to eight flexible spines, and a single spine heads the second. Many eleotrids have a well-developed swim bladder, although they are generally benthic (bottom-dwelling). Some have dull, brownish or dark coloration, while others are colorful. One species that lives in wells and sinkholes, Milyeringa veritas, is white or pinkish and has no eyes. Some eleotrids may be permanently sexually monomorphic (males and females alike), as is the case with most reef-dwelling gobies, but males of some species develop distinctive coloring for courtship, or when excited by the presence of a competitive male. During the breeding season a hump on the head behind the eyes appears on males in the species Hypseleotris galii. (Click here to see a fish diagram).
Other Physical Features: ectothermic ; bilateral symmetry
Sexual Dimorphism: sexes alike; male larger; sexes colored or patterned differently; ornamentation
Some eleotrids have dull coloring that may help them hide from predators, and some form dense schools, which protect individual fishes from predation.
Anti-predator Adaptations: cryptic
No information was found that addresses mating systems specifically in eleotrids, but Thresher (1984) includes Eleotridae in his general account of reproduction in the suborder Gobioidei. Gobies exhibit a wide variety of mating systems but most seem to be promiscuous, either organized into a hierarchical social system or small territories maintained by individuals. At least one species of eleotrid (Thalasseleotris adela) is usually found in pairs. In gobies, a typical mating sequence begins with nest preparation by the male, which involves clearing and cleaning the area where eggs will be deposited. The female’s readiness for spawning is evidenced by her swollen ventral area. The male swims back and forth between the female and the nest site and in some cases he will nudge her with his snout. Eleotrid courtship behavior probably follows a similar pattern, with some males assuming intense courtship colors and leading females to the nest.
Mating System: monogamous ; polygynous ; polygynandrous (promiscuous)
Eleotrids attach their eggs to vegetation or a substrate (bottom surface). Females in Hypseleotris compressa deposit up to 3000 eggs. No other information was found that addresses reproduction specifically in eleotrids, but Thresher (1984) includes Eleotridae in his general account of reproduction in the suborder Gobioidei. Most gobies have extended spawning seasons with peak spawning depending on the species, but in colder regions breeding may only occur once or twice a year. Females may deposit from five to several hundred eggs, which the male then fertilizes. In estuarine species the lunar cycle is thought to play a role in spawning behavior as well as larval recruitment.
Key Reproductive Features: iteroparous ; seasonal breeding ; gonochoric/gonochoristic/dioecious (sexes separate); sexual ; fertilization (External ); oviparous
Males in Hypseleotris compressa guard the nest. No other information was found that addresses parental care specifically in eleotrids, but Thresher (1984) includes Eleotridae in his general account of reproduction in the suborder Gobioidei. In most cases, male gobies guard the eggs after they are fertilized, and even if females are permanently paired they rarely take part in parental care. The young probably stay close to adults for a period of time after hatching. In some freshwater island species parental care is not practiced at all. Many eleotrids may fall into this category, since the larvae are carried downstream to the ocean where they feed and grow before ascending the freshwater streams.
Parental Investment: no parental involvement; male parental care
