Rectoris posehensis belongs to the order Cypriniformes, family Cyprinidae, subfamily Rectoris, and genus Rectoris posehensis. Commonly known as: oil fish, line fish, phoenix rock fish.
The body is long, nearly cylindrical, with a slightly raised back, a straight abdomen, and a flat and slender tail peduncle. The head is small, the snout is pointed, and the mouth is located below the mouth. The snout covers the upper jaw, and the edge is shallowly split into a tassel shape. The upper lip disappears, and the kiss skin is directly connected to the lower lip; the lower lip is thick and has a narrow area covered with papillae at the front edge. The lower jaw is separated from the lower lip, the upper jaw is curved, and the lower jaw is flat with a sharp edge. There are 2 pairs of barbels, the muzzle barbels are short and the jaw barbels are fine. The dorsal fin has no spines and the caudal fin is deeply forked. The body is silvery-white, the back is gray-black, there is a black longitudinal band along the lateral line from the upper corner of the gill opening to the base of the caudal fin, and the dorsal fin, pectoral fin and caudal fin are gray-black.
The straight-mouthed dace often inhabits rapids and shoals, and is a bottom fish that feeds on algae. The spawning period is from June to October, and they often flock to small river pits to lay eggs during flood periods.
Zhikou dace is a specialty fish of the Xijiang River system in Guangxi, and is also distributed in small quantities in the Minjiang River in Fujian.
There are two other species of the genus R. luxiensis, namely: R. luxiensis, which is distributed in the Yangtze River tributaries such as Yuanjiang in Hunan, Qingjiang in Hubei, and Daning River in Sichuan; and R. luxiensis, which is distributed in Yuanjiang, Yunnan, and Wujiang, Guizhou. R. mutabilis. The difference between these two species and the straight-mouthed dace is not obvious, and their habits are also the same.
The straight-mouthed dace is not large, with a common body length of 8-14 cm. It is known as the "oil fish" because of its high fat content.
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