In water bodies of the Far East rotan feeds on insect larvae of Chironomidae, Aedes, Chaoborus, Odonata; in a smaller amount, mostly in the young, on crustaceans Cladocera and Copepoda and larger individuals on small fishes (Berg, 1912, 1949; Yakovlev, 1925; Kirpichnikov, 1945; Nikolsky, 1956).
Diet of rotan in the natural distribution range was studied in greater detail by Sinelnikov (1976) in flood plain water bodies of the basin of the Razdolnaya River (Suifun). It is shown that feeding range of rotan is exceptionally wide. 76 components were noted in the diet. Cladocera are represented by 18 species, among which Chydorus sphaericus, Eurycercus lamellatus, Simocephalus elizabethae are predominant. Of Copepoda, 8 species were noted (juvenile stage are predominant in numbers).
Thus, of higher crustaceans rotan prefers juveniles of river crayfish and freshwater shrimp. Larvae of different aquatic insects Odonata, Ephemeroptera, Trichoptera, Coleoptera, Diptera (Chirinomidae, Heleidae, Tabanidae), have a significant role in the diet, larvae of chironomids are the major group, both in numbers and biomass. Juveniles of rotan are seldom predators, adults feed mostly on fish; young of rotan, bitterlings, minnows.
Since the character of feeding of rotan changes essentially with age the above author (Sinelnikov, 1976) distinguished 7 size groups: 5 mm, 8-11, 12-25, 26-40, 41-60, 61-100, 101-217 mm.
In larva 5 mm in length (with yolk sack) food has not been found. Fishes 8-11 mm in size actively feed. Their diet includes lower Crustaceans and chironomid larvae. Cladocera, particularly Chydorus sphaericus, are predominant in the number of individuals and in weight. Of Copepoda, mostly immature forms occur. Chironomid larvae are represented by very small individuals, therefore in spite of their abundance (58%) their weight does not exceed 22.5%. Single larvae of May flies are noted, algae and detritus.
In the young 12-25 mm in size food is more varied. Cladocera occur in larger numbers, however, by weight (48.4%) a predominant group are chironomid larvae. In fishes of this size group remains of fish food have been found in stomachs for the first time. A case is noted when 18 mm rotan swallowed a fish of the same species that was 7 mm in length. This facts suggests not only cannibalism, but also predation on early stages. Nevertheless predation for rotan of this size group is an exception rather than a rule, because all the recorded findings were single occurrences, and as a rule only mature individuals (more than 50 mm) feed on fish.
Juveniles 26-40 mm in length feed mostly on larvae of different aquatic insects among which chironomid larvae are predominant. Adult insects are frequently noted. The role of the lower crustaceans declines considerably: they constitute approximately 30% in weight.
Fishes 41-60 mm in length among which mature individuals occur nearly never feed on lower crustaceans and pass over to larger objects - larvae and adults of insects. Their diet begins to include freshwater shrimps, remains of fish also occur.
Rotan 61-100 mm in size feeds mostly on larvae of aquatic insects. It uses chironomids to a lesser extent (34.1 %). Fishes play an important role in its diet (11.1 %).
On the basis of data obtained three periods may be defined in rotan's feeding: planktonophagous (8-11 mm), benthophagous (12-100 mm) and predatory (more than 100 mm).
In the introduced range spectrum of feeding of rotan is also very wide - from cyclops and daphnia to fishes, only slightly inferior to it in sizes. Diet of rotan from the Upper Volga Basin was found to include 100 components (Shlyapkin, Tikhonov, 2001). When food is insufficient in water bodies large individuals of rotan eat smaller ones as in the natural water body (Bandura, 1979; Bolonev, et al., 2002; and many others. This is a factor allowing its populations to exist in any biocenoses and maintain abundance on a permanent level. Feeding on fry and juveniles of valuable fish species rotan replace them from a body of water and become the only species.
According to the data of Spanovskaya et al. (1964), feeding of rotan in a pond in the suburbs of Moscow in the first years after introduction in its qualitative composition was little different from food in Far Eastern water bodies. Juveniles 40 mm in length were feeding mostly on crustaceans (Cladocera, Copepoda), and larger ones apart from Cladocera (mostly Daphnia cucullata), consumed insect larvae of Chironomidae, Ephemeroptera, Odonata, Coleoptera, Chaoborus, Heleidae, Trichoptera, Hemiptera.
In 1961-1962 quantitative composition of food of rotan in comparison to 1955-1956 changed drastically. Percentage of Cladocera in fishes with sizes of 40-60 mm remained relatively high, but Chydoridae (Chydorus, Camptocercus) crayfish inhabiting algae, Daphnia and Bosmina inhabiting water column occurred in larger individuals of this group and in fishes 60-105 mm in length.
Larvae of Odonata, Coleoptera, Hemiptera nearly disappeared from the diet, the role of larvae of Chironomidae declined notably and their species composition changed. In 1955-1956 larvae of Tanytarsus, Polypedilum, Einfeldia gr. carbonaria, Limnochironomus gr. Nervosus were predominant, whereas in 1961-1962 larvae of Orthocladiinae (Cricotopus gr. silvestris, Psectrocladius gr. psilopterus) and Corynoneurinae, associate with fouling communities were more common. It was not until 1961 that rotan in that pond began consuming its own juvenile. Cannibalism was noted in individuals that had attained a length of 45 mm. In fishes more than 60 mm in length more than a half of food consumed were its juveniles. Moreover, rotan ate tadpoles that are seldom consumed by fishes.
The change for feeding on its juveniles and tadpoles is assigned (Spanovskaya et al., 1964) to an abrupt impoverishment of the fauna of large invertebrate (beetles, their larvae, larvae of dragonflies) differing from planktonic forms by a low rate of reproduction and complete elimination of crucian carp on the stage of eggs, larvae and juveniles.
Feeding on larvae and adults of amphibians was described for rotan from suburbs of Moscow (Manteifel, Reshetnikov, 1997, 2001; Reshetnikov, 2001; Reshetnikov, Manteifel, 1997) from the Transcarpathian region (Litvinchuk, Borkin, 2002). Fragments of larvae of Вufo bufo were found in intestines in 6 specimens (3 females and 3 males) of 31, having absolute length from 100 to 161 mm. On the average stomachs of rotan that had consumed larvae of toads contained 4 ± 1.41 В. bufo (1 to 10.). Rotan consumes larvae of two species of tritons Triturus cristatus
and T. vulgaris
, and adults of the former (Reshetnikov, 2001; Reshetnikov, Manteifel, 1997), and also larvae and adult individuals T. dobrogicus
(Litvinchuk, Borkin, 2002).
For water bodies of Mordovia (Volga River basin) it also shown (Vechkanov, 2000) that the many generation population of rotan uses nearly the entire food supply of the water body. For instance in flood plain lakes of the Sura River this fish consumed up to 70 different representatives of invertebrates, including molluscs and its own juveniles on larval statge. For several years the extremely dense population of the species of the could devastated the whole fauna of the water body. For instance, in Lake Pyzhovka (Surskaya flood plain) where a powerful population of rotan was formed only 12 forms of invertebrates were found instead of 40-60 representatives usual in such lakes.
On the whole diet of rotan in different water bodies of Baikal Region was recorded to contain approximately 100 species of food organisms belonging to 57 genera and 30 families with a maximum diversity of larvae and pupae of chironomids (28 species) and caddis flies (Pronin et al., 1988). In all water bodies rotan feeds on animal food and is characterized as an euryphage. The young of rotan consumes in large amounts small animals inhabiting in the water. At the age from one year to four years rotan is mainly a benthophage (consuming organisms living on the bottom of the water body) and partially a predator. Older age groups (on the fifth or sixth year of life) consume in large amounts the young of fishes, particularly carps.
In fish culture ponds according to the data of Elovenko and Klimova (1983) and Elovenko (1984) juveniles of rotan in the first week of life feed on phytoplankton, than changes for Cladocera and Copepoda crustaceans. When fishes attain a length of 12-15 mm chironomid larvae become a predominant group, they dominate in stomachs of rotan up to 110 mm in length. Species composition of chironomid larvae as a rule is represented by swimming forms.
Fishes up to 40 mm in length consume molluscs, larvae, May flies, beetles other Diptera, dragon flies (during moulting), caddis flies. The portion of crustaceans in food clots is disappearing. In individuals 20 mm in length, fish eggs and larvae (including those of its species) appear in stomachs; the portion of fish food increases with growth and in individuals of more than 110 mm in length it is of primary importance. Chironomid larvae have lower mass than fish food. Among fishes in fish culture ponds rotan prefers to consume those unamoured: minnows, bleaks, gudgeons, common bitterling, pike, crucian carp, its own juveniles as compared to ruffe, perch, loach and wild carp. According to the data of Zaloznykh (1982) for rotan from ponds of Ili fish farm, food of individuals of older age classes comprised up to 97% of fish objects, at the end of summer and in the autumn its own juveniles comprised up to 82 %.
Consumption of food objects very different in size and behaviour is possible because rotan possesses a number of morphological features characterizing it as an active catcher and a potential predator.
Rotan has a large mouth (hence its name in Russian); teeth are present on the dentary and premaxilla, on the lower and upper elements of the hyoid arch, on the upper elements of two last gill arches. Gill rakers (9-10) are knob-shaped covered with setae assembled in bunches, assist in keeping the prey in the mouth. Relative size of head increases with growth jaws become longer, which facilitates capturing large prey.
Makhlin (1960) indicates that rotan in aquarium readily capture guppy, juveniles of crucian carp. Results of aquarium observations in the selectivity of rotan to different foods show that when sufficient amount of different large invertebrates (for example, larvae of dragon flies) rotan with a size of approximately 60 mm much more readily feed on them than on fish. Larger individuals feed on fish, but they retain a high degree of selectivity in relation to large invertebrates.
In the opinion of Spanovskaya and others (1964) and Elovenko (1984) rotan does not feed on juveniles of its own species if other food is sufficient. Feeding on invertebrates, is apparently more characteristic of this species; the change for feeding on juveniles of its species, tadpoles is attributed to the unfavourable feeding conditions in connection with the deterioration of the state of food supply.
Yakovlev (1925) describes "hunting" of rotan in an aquarium. It notices the prey rapidly at a distance, but never attacks it immediately, it begins approaching it gradually, with stops, along a straight line, moving only its pectoral fins, not moving its caudal fin and permanently looking at the prey; only after it approaches the prey it seizes the prey by a swift sharp movement.
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