Biological characteristics of the Siberian gudgeon Gobio sibiricus (Cyprinidae) and its infection with metacercariae Opisthorchis felineus in the Tom River basin (Tomsk Oblast, Russia)

In the Ob basin, the Siberian gudgeon Gobio sibiricus Nikolsky, 1936 is widespread in the river system. This species is a typical rheophile; it prefers tributaries of the first and second orders and adheres to coastal areas of rivers with rocky-pebble, pebble-sandy soils. The biology and morphology of the Siberian gudgeon are currently poorly studied, and there are also questions related to the taxonomy of Siberian gudgeon. The species is also interesting from the point of view of its contribution to the circulation of trematodoses. Being representatives of the carp family, gudgeon can be intermediate hosts of trematode metacercariae, including opisthorchis. In this regard, an interesting fact is that the Siberian gudgeon is included in the opisthorchiasis outbreak operating in Tomsk Oblast. Almost all territories adjacent to the Ob-Irtysh basin are unfavorable for opisthorchiasis. Tomsk Oblast is one of the leaders in terms of population infected with cat fluke. For reservoirs of Tomsk Oblast, it was previously indicated that gudgeon was free from opisthorchis invasion. In other regions within the Ob-Irtysh basin, infection of gudgeon with opisthorchis was noted in the Chumysh River (Kemerovo Oblast), in small rivers in the south of Tyumen Oblast, in Novosibirsk Oblast. The aim of the work was to study the biology of gudgeon and assess the level of its infection with opisthorchis metacercariae in tributaries of the Middle Ob. Gudgeons have no commercial value, they are objects of amateur fishing, they are used both as food for humans and domestic animals, although its share in human preferences is not large, about 1%, its share in catches in second-order tributaries is quite large, on average, about 25%. The material for the study was obtained during monitoring studies of fish biodiversity in water bodies of Tomsk Oblast, in the south of Western Siberia. The Tom River is one of the major right tributaries of the Ob River. A significant part of the lower section of the river is located within Tomsk Oblast. The largest tributaries of the Tom (in the lower reaches) are the Basandaika and the Ushaika rivers (right-bank tributaries of the 1st order). The material on the gudgeon was collected from 2000 to 2024. The Ushaika River, 2000 - 71 specimens, the Basandaika River, 2010 - 35 specimens, 2020 - 10 specimens, the Tom River, 2004 - 78 specimens, 2005 - 38 specimens, 2009 - 43, 2024 - 17 specimens. The ichthyological material was analyzed using morphological and biological analysis methods. Muscle infestation of gudgeon with Opisthorchis felineus metacercariae was studied using the conventional compressor method. Morphological characteristics of the Tom River gudgeon: SL 124.7 mm, D II 7, A II-III 6, V I 7, ll 41.7; the antedorsal distance (47.4% SL (standard length)) is greater than the postdorsal (42.9% SL); the height of the caudal peduncle (8.4% SL) is 33.2% of the head length (25.0% SL) and 38.5% of the caudal peduncle length (18.7% SL). Gudgeon in the Tom River basin are found at the age of up to 7+ years. The size characteristics of the gudgeon vary somewhat, so it can be noted that the gudgeon from the Tom River is larger, while the gudgeon from the Basandaika River is smaller (See Table 1). In the Ushaika River, gudgeon was noted with an average body length of 103.8 and a body weight of 16.8 g, in the Basandaika River with an average body length of 70.4 mm, a body weight of 6.4, and in the Tom River with an average body length of 110.7 mm, a weight of 23.2 g. The food spectrum of the gudgeon of the lower Tom River consisted of: chironomid larvae, mayflies, caddisflies, crustaceans, bivalves, beetles, and detritus. The majority of the gudgeon's food spectrum consisted of mayfly and caddisfly larvae (more than 50%). The gudgeon becomes sexually mature at the age of 2+ years. Spawning of the gudgeon in the Tom River is portioned, begins in the first ten days of July and can stretch until the end of July. Individual absolute fecundity varies considerably (3406-21984 eggs, average - 11588 ± 1502) (See Table 2), increasing with the size of the fish. We have established that gudgeon, like most other carp fish, despite its confinement to fast-flowing water bodies and spawning in the summer period, is susceptible to invasion by O. felineus metacercariae. The average long-term infestation (PI prevalence of infection) of the gudgeon in the Tom River basin was 8.3%, the intensity of infestation was 1.75 metacercariae/individual. Some differences in infestation in different water bodies are observed; the gudgeon from the Tom River was more infested (See Table 3). An assessment of the dependence of the infection level on the size of the fish was made. According to our data, no such dependence was found, however, it can be noted that among the largest fish (Tom River, 2009) no infected individuals were noted (See Fig. 1). The article contains 1 Figure, 3 Tables, 37 References. The Authors declare no conflict of interest.

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