Morphological abnormalities in the skeleton of juvenile fish from the Kacha river (Middle Yenisei system) in the gradient of anthropogenic impact

The predominant part of small rivers of Russia is subject to active technogenic impact. The most critical is manifested in urban and suburban water bodies, taking on a huge number of organic and inorganic pollutants. The striking example of such impact in the Yenisei river basin is the Kacha river (64°00'58''N, 92°53'32''E), the lower course of which is located within the city of Krasnoyarsk and constantly exposed to technogenic pollutants. The intensive technogenic load, as a rule, negatively affects the communities of hydrobionts, including juvenile fish, which have the lowest level of toxic resistance in comparison with adults and are also unable to actively leave areas with high levels of pollution. One of the responses of the fish community to the effect of a complex of unfavorable factors caused by the anthropogenic load on water bodies, including the presence of toxic substances in the ecosystem can be the emergence of various morphological abnormalities. This fact makes it possible to use the indicators of occurrence and diversity of morphological abnormalities as criteria for water quality assessment. The aim of this research was to evaluate the diversity and the occurrence of skeletal abnormalities in juvenile Siberian gudgeon Gobio gobio cynocephalus Dybowski, 1869 and common minnow Phoxinus phoxinus (L., 1758) from the Kacha river (Middle Yenisei system). The material for the study was selected in July-August 2016, at four sites of the river differing in the level of technogenic pressure and the spectrum of pollutants (See Fig.1). The list of the main polluting agents, as well as the summary information on the environmental monitoring results at the investigated sites of the river are given in Table 1. In total, 184 Siberian gudgeons and 212 common minnows were examined. The size and age characteristics of the studied individuals are shown in Table 2. Abnormalities were studied in specimens previously cleared of soft tissues and stained with alizarin red according to the Potthoff method with a 40* increase. The examination was carried out in 9 parts of the skeleton, successively (See Table 3). Nomenclature and differentiation of abnormalities in terms of severity are given according to Chebotareva (2009) and Boglione et al (2002). To describe the type and location of the abnormality, a system of symbols was used according to which each part of the skeleton was assigned an alphabetical index; a particular abnormality type got a numerical index (See Table 3). The frequency of abnormal specimens, the total spectrum of abnormalities, the frequency of abnormalities, the relative occurrence of abnormalities, the number of abnormalities in an individual, and the load of severe abnormalities were studied. The incidence of abnormalities and occurrence of abnormal specimens were compared using contingency tables 2*2 with an estimate by Chi-squared test with p <0.01. Confidence intervals for occurrence at different sites were calculated using Wilson method. Differences in the number of abnormalities were investigated by the Kruskal-Wallis test. In total, 95 abnormalities belonging to 12 types were detected. Among them, 62 abnormalities belonging to 7 types in juvenile gudgeons and 33 abnormalities belonging to 10 types in juvenile minnows were identified (See Tables). Abnormalities were localized predominantly in the abdominal part of the vertebral spine and presented a variety of neural and hemal arch deformation, such as unclosed vertebral arches, fusion of vertebral arches and displacement of arches to adjacent vertebrae. The incidence of abnormalities varied from 6.5 to 55.7% in juvenile gudgeons and from 8.4 to 75.0% in juvenile minnows. The incidence of abnormal specimens was 4.6-10.4% for gudgeons and 7.4-11.7% for minnows. Proportions of severe abnormalities in juveniles of two species were similar and ranged from 80 to 0% from the upper reaches of the river to the lower. When analyzing the occurrence of abnormalities in the Kacha river, a tendency to increase the frequency of occurrence was witnessed as the anthropogenic load on the watercourse increased. In general, the occurrence of skeletal abnormalities in the Kacha River lower reaches was close to the occurrence of the vertebral spine abnormalities in juvenile fish, previously noted in a few suburban waterways near Krasnoyarsk. The paper contains 3 Figures, 4 Tables and 34 References.

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