Taxonomy
- Kingdom: Animalia
- Phylum: Chordata
- Class: Actinopterygii
- Order: Gobiiformes
- Family: Odontobutidae (freshwater sleepers)
- Genus: Perccottus (monotypic)
- Species: Perccottus glenii Dybowski, 1877
Common names
The species is commonly known as the Chinese sleeper, Amur sleeper, or rotan (in Russian).
Description
The Chinese sleeper is a small freshwater fish reaching up to 25 cm (9.8 in) in total length, with a maximum recorded weight of about 250 g (8.8 oz). Its body is elongate and somewhat compressed, resembling perch, ruffe, or sculpin. The head is rounded with a slightly protruding lower jaw; the eyes are positioned high on the head. The dorsal fins are closely spaced, the anterior dorsal fin bearing six to eight spines and the posterior dorsal fin having nine to eleven soft rays. The anal fin contains one to three spines and seven to ten soft rays. Pelvic fins are separate, a feature that distinguishes the species from many gobiids. The overall coloration is brownish with a checker‑board pattern of darker markings or bars, and radiating dark lines are present on the head.
Distribution and habitat
Native range: The Chinese sleeper is native to the Amur River basin and adjacent waters of northeastern China, the Russian Far East, and northern North Korea.
Introduced range: Since the early 20th century it has been introduced to numerous water bodies across Europe and western Asia, including the Baltic Sea basin, the Danube drainage, the Black Sea region, and parts of Central and Western Europe. Established populations are now documented in countries such as Russia, Ukraine, Latvia, Germany, Finland, and the United Kingdom.
Habitat: The species occupies lentic and slow‑moving freshwater habitats—ponds, small lakes, irrigation canals, and low‑gradient streams—often with abundant aquatic vegetation. It tolerates a wide range of environmental conditions, including low oxygen levels and moderate pollution.
Ecology
The Chinese sleeper is an opportunistic predator. Its diet consists mainly of aquatic insects and their larvae, small crustaceans, and fish fry. Reproduction occurs in warm, shallow vegetated areas; females lay adhesive eggs among submerged plants, and males guard the clutch until hatching. The species can produce multiple spawning events during the breeding season, contributing to its rapid population growth in introduced areas.
Invasiveness
The fish is regarded as an invasive alien species in many parts of Europe. Its adaptability, high reproductive output, and broad diet enable it to outcompete native benthic and small pelagic fishes, as well as amphibians. Documented ecological impacts include reductions in native fish abundance, alteration of invertebrate communities, and, in some cases, the formation of monospecific fish assemblages. The European Union has listed the Chinese sleeper among Invasive Alien Species of Union concern (since 2016), restricting its import, breeding, transport, commercialisation, and intentional release.
Human interaction and economic importance
In its native range the Chinese sleeper has minor commercial value and is occasionally kept in aquaria. In introduced regions it is considered a nuisance species because of its potential to damage local fisheries and biodiversity. Control measures typically involve mechanical removal, habitat modification, or public awareness campaigns to prevent further releases.
Conservation status
The International Union for Conservation of Nature (IUCN) classifies Perccottus glenii as Least Concern, reflecting its wide native distribution and large, stable populations. However, its invasive status in non‑native regions has prompted management actions to curb further spread.