One of the predators of the ichthyofauna of the Lower Tobol is Esox lucius (Linnaeus, 1758) (Esociformes, Esocidae). The purpose of this work is to study the current state of the E. lucius parasite fauna in the lower reaches of the Tobol River. In the present study 47 individuals of the northern pike of different sex aged from 2+ to 8+ years were examined by the method of complete parasitological dissection. As a result of the research, 23 types of parasites were found in the pike. The largest number of species of parasitic organisms – 20 – were found in May, 12 were found in December and 11 in September. Of these, 10 species are specific to northern pike: Haemogregarina esoci (Nawrotzky, 1914), Chloromyxum esocinum (Dogiel, 1934), Myxidium lieberkuhni (Biitschli, 1882), Myxosoma anurum (Cohn, 1895), Henneguya psorospermica (Thelohan, 1995), Tetraonchus monenteron (Wagener, 1857), Gyrodactylus lucii (Kulakowskaja, 1951), Triaenophorus nodulosus (Pallas, 1781), Azygia lucii (Miiller, 1776), Raphidascaris acus (Bloch, 1779). For the first time an intraerythrocyte parasite – H. esoci – was found in pike in the Lower Tobol, the extensiveness of invasion was 18.7% in December, and 6.2% in May. Epistylis sp. and Trichodinella epizzotica parasitized on the surface of the body of fish only in May, whereas members of the genus Trichodina were found in winter and spring. In all seasons, parasitization by M. anurum and H. psorospermica was established on the gills. The greatest occurrence of spores of M. lieberkuhni and C. esocinum was observed in the spring. Myxosporidia parasitized in the kidneys and T. monenteron parasitized on the gills during all periods of the study (the latter with an extensivity of invasion of 100.0%). All examined fish are infected with T. nodulosus 100.0% of cases. In May, other types of cestodes were found: P. esocis and Dibothriocephalus latus. Three pike were infected with proteocephalis. The larval stage of diphyllobothriid was found in one fish in the liver and gonads in an amount of 139 individuals. In the pikes’ stomach, during all periods of the study, A. lucii was found in all the fish examined. In the autumn period of the study immature R. campanula were found in in the intestine of 4 fish specimens. The nematode R. acus was found in pike only in spring. This nematode was found in fish aged 4+–8+. In May, glochidia with a high intensity of invasion were found on fins, gill covers and gills of fish. E. sieboldi copepods were found on the gills; in May, one specimen was found in one pike and in September in 6 with AI of 0.7. Tetraonchus monenteron was a dominant species, in May its degree of dominance decreased with the greatest uniformity of species in this study period. Having considered the age dynamics of pike infection by various types of parasites, it was found that in the age group 4+–5+ the number of species of parasites was greatest (20), while in groups 2+–3+ and 6+–8+ it was 14. In the pike, the core parasitic fauna were M. anurum, H. psorospermica, T. monenteron, T. nodulosus, A. lucii. Seasonality has virtually no effect on the degree of infection with specific parasites. The age of fish largely determines the qualitative and quantitative composition of the parasite fauna.
In the basin of the Irtysh River, one of the mass representatives of the Acipenseridae family is the Siberian sterlet Acipenser ruthenus marsiglii (Brandt, 1833). Today, the catch of sterlet in this region is allowed only as control catches for scientific research. Poaching causes a great loss for the species. In the period from 2013-2016 there were held 44 forensic and ichthyologic examinations, including 26 criminal case examinations and 18 expert examinations on the materials of the Register of Complaints concerning Offences. 665 species of Siberian sterlet were caught illegally. In these illegal catches, species with a body length of 31.0 to 40.9 cm were most often found (this made 55.2% of all years of expert examinations), species of 21.0-30.9 cm length made 26.3%, of 41.0 to 50.9 cm length made 16.4%. When analyzing the total mass of fish caught illegally from 2013 to 2016, it was found that species having a mass 100.0-199.9 g were most often found, their share of the total number of fish was 51.6%. Species with a mass 200.0 - 299.9 g made 17.1%; with a mass 0-99.9 g - 15.6%. In this study, the minimum number of lateral beetles in sterlet was 49; maximum - 69; dorsal beetles 11-18; the number of gill rakers corresponded to the specific number and varied from 17 to 29 (mean 14). The meristic features of the species under study correspond to the subspecies Siberian sterlet Acipenser ruthenus marsiglii (Brandt, 1833).
The article describes the problems of the Ob-Irtysh basin (the Tyumen region), which is a natural focus of opisthorchosis. Localized in the bile ducts of the liver, the pathogen of opisthorchosis poses a risk to the human body. Parasitic community of Siberian roach inhabiting the Tobol Riverwas studied in the autumn period of its life cycle. There were examined 24 fish species of different sexes at the age of 0+ to 4+. There was registered the roach invasion by 9 species of para-sites belonging to 6 systematic groups: Monogenea - 2, Cestoda - 1, Trematoda - 4, Nematoda - 1, Bivalvia - 1, Copepoda - 1. Parasitization of gills by monogeny Dactylogyrus crucifer with inva-sive extensiveness of 83.3% and Paradiplozoon homoion homoion with invasive extensiveness of 16.7% has been stated. Diplostomum chromatophorum parasitizes in the lens of the eye, in total 18 of the examined fish are invaded. Opisthorchis felineus was found in muscles with invasive exten-siveness of 29.2%. Immature specimens of Sphaerostoma bramae were found in the intestines of nine fish examined. Mesentery of 4 fish species and liver of 1fish species examined are affected by Raphidascaris acus at a larval stage. The dominant parasite in the study is Rhipidocotyle campanula. Trematode at the metacercaria stage was found on the gills and fins, the overall infection rate comes to 70.8%. Also, Ergasilus sieboldi parasitizes on the gills and fins of the examined roach species. Depletion of the species composition of parasites is observed in the autumn period of the roach life cycle.
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