Eleotridae is a family of fishes of the order Perciformes. Includes more than 40 genera, more than 300 species. Inhabitants of marine coastal and fresh waters of rivers and lakes of tropical, subtropical and temperate latitudes. Most species are found in the tropical Indo-Pacific region, but there are also species in subtropical and temperate regions, warmer parts of North and South America, and near the Atlantic coast in Africa. Many eleotridae pass through the planktonic stage at sea, and some spend their entire lives at sea. As adults, most live in freshwater streams and brackish water. One of its genera, Caecieleotris, is troglobic. They are especially important as predators in freshwater stream ecosystems on oceanic islands such as New Zealand and Hawaii, which otherwise lack families of predatory fish typical of nearby continents, such as catfish. Anatomically, they resemble the Gobiidae, although unlike most gobies, they do not have a pelvic sucker. Eleotridae are small fish that live on substrate, often among vegetation, in burrows, or in crevices in rocks and coral reefs. Although eleotridae resemble gobies in many ways, sleeping gobies lack a pelvic fin sucker, and this, along with other morphological differences, is used to distinguish the two families. Gobiidae and Eleotridae probably have a common ancestor, and they are both placed in the order Gobiiformes, along with several other small families containing gobies. Their body coloration is mostly very modest (except for coral reef dwellers), which seems to be due to the exceptional ability of these fish to mimicry. They are able to quickly change their coloration from dark brown to pale gray, with the body then appear clear-cut spots or stripes, the body becomes monotonously pale. Distinguish these fish from above in their surroundings is extremely difficult, which saves them from predators. On the contrary, eleotris that live among coral reefs, have a bright coloration, catching the eye. Most species are marine coastal fish. Some species are exclusively marine fish, inhabiting shallow bays and coral reefs.
Dormitator and Eleotris, the two most common and typical genera, include many species inhabiting marine, estuarine and freshwater habitats. Among the largest members of the family are predatory species such as Gobiomorus dormitor, measuring up to 90 cm (3.0 ft.) in freshwater near the West Atlantic and Dormitator maculatus, which grows to 70 cm (2.3 ft.) and is widely distributed in fresh and brackish and shallow marine waters of the southeastern United States and Mexico. Most, however, are much smaller, such as the freshwater and brackish-water species from Australia and New Guinea, including Hypseleotris, known as gudgeons (not to be confused with the Eurasian freshwater carp Gobio gobio, also known as gudgeon and after which the Australian sleeping gobies were probably named). Some, such as the gudgeon (H. compressa) and peacock gudgeon (Tateurndina ocellicauda), are sometimes kept in aquariums. The smallest in the family are the Amazon leptophilipnion with a standard length of less than 1 cm (0.4 inches). The best known is Perccottus glenii. The scales are cycloid on the back and ctenoid on the belly and flanks. The jaws have small bristle-shaped teeth. Occurs in the northeast of the Korean Peninsula, China, and Primorye. It is common in the middle and lower reaches of the Amur River and its tributaries. It is introduced to Central Asia and the European part of Russia. It is known in the lakes near Baikal and in the surrounding water bodies of Tomsk. Lives in shallow overgrown and polluted ponds, extremely undemanding to habitat conditions. Matures in the second year of life. It spawns in June-July, in batches. The male guards the clutch. An avian predator, it consumes aquatic insects and their larvae, tadpoles, and young fish. It has no commercial value. It is an object of amateur fishing. Feed on insect larvae, crustaceans, and juvenile fish, including its own. No mosquito larvae, which it destroys in the first place, are present in water bodies inhabited by the tadpole. The tadpole is unusually undemanding and can live and breed in heavily polluted bodies of water and under such natural conditions that other fish cannot withstand. It lives, for example, in small temporary reservoirs that often dry up in summer and freeze through in winter. Fish in these cases burrow into a thick layer of silt and experience adverse conditions there. In summer they die only when the bottom silt dries out. They also live in cold marshes, in overgrown lakes and in heavily heated reservoirs. In cases when a water body dries up, they reappear in it after the water body is filled with rainwater.