Predators to a large extent control rotan abundance. In the Amur River more than 10 species, including bagrids and snakehead, feed on rotan. It is assumed that rotan abundance is controlled mostly by snakehead (Bolonev et al., 2002).
Elovenko and Klimova (1983) studied food relations between rotan and hydrobionts in fish culture ponds of Khankaisky fish factory, Khabarovsk fish-farm (native distribution range) and fish factory "Nara" of Moscow Region. In ponds, catfishes, pike, bagrids, snakehead, common perch and ruffle feed on rotan.
Among these, snakehead and perch feed on rotan most intensively. Eggs and juveniles of rotan are destroyed by bugs Notonecta glauca, Nepa cinerea, Naucoris cimicoides, Ranatra linearis, Sigara hellensii, S. falleni, Micronecta griseola, etc., beetles Dytiscus marginalis, Hibius ater, larvae of dragon flies Lestes sponea and L. nympha. Among the predatory invertebrates maximum damage to rotan progeny is caused by bugs, which in small amounts are consumed by adult specimens of rotans. In growth ponds juveniles of rotan are competitors for food to many species of gobies, ruffe, perch, minnows, loaches; to common bitterling and other fish species for chironomid larvae and crustaceans and among reared fishes to yearlings of carp, crucian carp, Amur wild carp and Amur pike.
In the Baikal system, density of rotan ranged from 41 to more than 4,000 per hectare. Densities were highest in oxbow lakes where there was no current and lowest in the river channels where the current was swift (Litvinov, O'Gorman, 1996). Feeding relationships of rotan with local species of fish are relatively tense. This is clearly seen in water bodies of the delta of the Selenga River where in similarity of food the maximum antagonism is with ide (up to 90%), crucian carp (81.2%) and roach (67.3%), to a lesser extent with dace (49.4%) (Pronin et al., 1998).
Shlyapkin & Tikhonov (2001) in the Yaroslavl Region inspected 17 reservoirs populated by rotan. In two reservoirs all kinds of fish were absent before the rotan introduction. Native fish communities of other reservoirs included 1-8 species of fishes, such as verkhovka Leucaspius delineatus (Heckel), roach Rutilus rutilus (L.), crucian carp Carassius carassius (L.), tench Tinca tinca (L.), perch Perca fluviatilis L. and pike Esox lucius L. As a result of rotan introduction in two reservoirs with one-species fish communities amur sleeper completely has superseded "verkhovka", which previously was a mass species. Multispecific fish communities with predatory fishes such as perch and pike are steadiest against the occurrence of the new species (Elovenko, 1980; Kudersky, 1980; Vechkanov, 2000).
According to the data of Zaloznykh (1982) for Gorky Region (Volga River basin) in bays of the Sarma River and in small water bodies periodically connected with river rotan occurs very seldom, even though a large number of juveniles enter this river from growth ponds of Ilevsky fish farm. Also accidental are occurrences of rotan in old river beds and flood plain lakes of Oka River, regularly inundated where predators perch and pike are common components of their ichthyofauna.
At the same time in small water bodies isolated from rivers, where deficit of oxygen often arises and inchtyocenoses consist mostly of roach and crucian carps, rotan is sometimes predominant. Obviously, such is the case with P. glenii in the biocenosis of Lake Glubokoe. In 1981, P. glenii was found in considerable numbers in the littoral, mainly in areas overgrown with water thyme; a catch made in shallow water showed a predominance of individuals up to 7 cm long, whereas individuals more than 10 cm long were rare. One individual 16 cm long and weighing 80 g was caught. In subsequent years the numbers and size of this fish in Lake Glubokoe have not changed considerably (Manteifel, Bastakov, 1986).
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