Sleeper gobies are members of the Eleotridae fish family, found predominantly in the tropical Indo-Pacific, with about 35 genera and 182 species. While many eleotrids pass through a planktonic stage in the sea and some spend their entire lives in the sea; as adults, the majority live in freshwater streams and brackish waters. A few species (e.g., Milyeringa, Typhleotris, and some Bostrychus) are troglobitic. They are especially important as predators in the freshwater stream ecosystems on oceanic islands such as New Zealand and Hawaii that otherwise lack the predatory fish families typical of nearby continents, such as catfish. Anatomically, they are similar to the gobies (Gobiidae), though unlike the majority of gobies, they do not have a pelvic sucker.
Like the true gobies, they are generally small fish that live on the substrate, often amongst vegetation, in burrows, or in crevices within rocks and coral reefs. Although goby-like in many ways, sleeper gobies lack the pelvic fin sucker, and that, together with other morphological differences, is used to distinguish the two families. The Gobiidae and Eleotridae likely share a common ancestor, and they are both placed in the suborder Gobioidei, along with a few other small families containing goby-like fishes.
Dormitator and Eleotris, two of the most widespread and typical genera, include a variety of species that inhabit marine, estuarine, and freshwater habitats. For example, the fat sleeper goby (Dormitator maculatus) grows to over 1 ft (30 cm) and is widely found in fresh to brackish and shallow marine waters of the southeastern United States and Mexico. Some predatory sleeper gobies grow much larger, such as the marbled sleeper goby, Oxyeleotris marmorata, a freshwater species from Southeast Asia that can grow to 2 ft (60 cm) long. However, most are much smaller, such as the fresh- and brackish-water species from Australia such as Hypseleotris spp., known locally as gudgeons (not to be confused with the Eurasian freshwater cyprinid Gobio gobio, also known as the gudgeon and after which the Australian sleeper gobies were likely named).
The Eleotridae are divided into two subfamilies, Eleotrinae and Butinae, with these genera:
- Subfamily Butinae
- Subfamily Eleotrinae
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