About Perccottus glenii Dybowski, 1877
Perccottus glenii Dybowski, 1877, commonly called Chinese sleeper and known as rotan in Russia, has a body shape that resembles perch, ruffe, or sculpin. Its eyes are set high on the head, which has a rounded snout and a projecting lower jaw. The two dorsal fins have little to no gap between them; the front dorsal fin has 6 to 8 spines, and the rear dorsal fin has 9 to 11 soft rays. The anal fin has 1 to 3 spines and 7 to 10 soft rays. Unlike gobies, the pelvic fins of this species are not fused together, a feature used to distinguish the two. The second dorsal fin and anal fin are both more rounded and shorter than those of gobies, and the caudal fin is also more rounded than that of gobies. Its overall body color is brownish, with darker markings arranged in a checkerboard pattern or as dark bars. Dark lines radiate out from the eye across the head. This species can grow up to 25 centimetres (9.8 in) in total length, and the heaviest recorded specimen weighed 250 grams (8.8 oz). Chinese sleeper is native to the inland waters of northeastern China, northern North Korea, and the Russian Far East. In 1912, a scientific expedition brought specimens from the River Zeya to Saint Petersburg to keep as ornamental fish. During the 1920s, Chinese sleeper invaded many bodies of water around Saint Petersburg. By the 1950s, it was found in the shallow waters of the Gulf of Finland in the Baltic Sea, where it was classified as an invasive species. Its typical habitat includes ponds, enclosed water bodies, and slow-moving streams. The westernmost location in Chinese sleeper's current range is ponds in the Bavarian Danube basin in Germany. A single occurrence of the species has been recorded in a mesohaline environment in the northwestern Black Sea in Ukraine.
