This study reveals the diet of pike-perch from two habitats within the Tersko-Caspian region. The feeding habits of pike-perch in the Sulak and Terek rivers and Tersko-Caspian region were investigated based on 354 specimens sampled monthly from a commercial catch in 2019. Their diet consisted of different prey, with fish representing the most important prey group (up to 90%). Rutilus caspicus dominated with a frequency of occurrence of 20.5, and Aspius aspius, Perca fluviatilis, and Chondrostoma oxyrhynchum, had 13, 9.5, and 8.3%. In the earlier ages 1+ and 2+, zooplankton dominated, followed by mysids and chironomids, which continues into the older ages but at decreasing rates. Analysis of monthly variations in stomach fullness indicated that feeding intensity fluctuated in time, with the highest values in March–April, and lowest in September and November. It was found that the diet of pike-perch in the western Caspian changed considerably from season to season. They begin to actively feed after wintering and before, or even during, spawning period. The spectrum of the diet of Sander lucioperca includes more than 20 elements, mainly juveniles of commercially valuable fish. This fish is characterized by a relatively low ontogenetic diet diversity and flexibility, which makes it sensitive to environmental changes, including anthropogenically induced ones. This fish partially compensates for this disadvantage with its lifestyle, namely, its active foraging movements and migrations from fresh water to salt water and back, following its prey species.

The northern section of the Caspian Sea is an important fishery for Kazakhstan. In the present study, a total of 606 individuals of 13 fish species were collected. For each of Abramis brama, Alosa saposchnikowii, Atherina boyeri caspia, Carassius auratus, Clupeonella cultriventris, Cyprinus carpio, Liza aurata, Leuciscus aspius, Rutilus rutilus caspius, Sander lucioperca, Sander marinus, and Sander volgensis 50 individuals were examined whilst 6 individuals of Siluris glanis were examined. The nematode parasite Anisakis schupakovi was found in all fish species except Liza aurata, Carassius aurata, Cyprinus carpio and Rutilus rutilus at intensities ranging from 1 to 1197 parasites per infected fish. Trematodes of family Diplostomidae were also isolated from all fish except Alosa saposhnikowii, Clupeonella cultriventris and Sander marinus at intensities ranging from 1 to 242 parasites per infected fish. Other parasites found included the nematodes Porrocaecum reticulatum, Contracecum sp, Camallanus sp and Eustrongylus excisus; the cestodes Neogryporhynchus cheilancristrotus, Bothriocephalus opsariichthydis; the monogenean parasites Mazocraes alosa, Ancyrocephalus paradocus, Gyrodactylus spp, Ligophorus vanbenedenii and Dactylogyrus spp; and the crustacean parasites Ergasilus sp. and Synergasilus sp. In addition one unidentified species of nematode and a bivalve of the genus Unio was recovered from Rutilus rutilus caspius. There was no association between Fulton’s condition index and intensity of parasite infection.

The study of planktonic animals of the Caspian Sea is topical and, during the last centuries, has brought and continues to bring new results. This is an inevitable process attributed to the introduction of non-indigenous predatory representatives of zooplankton by ballast water of ships. During the study period, the zooplankton of the Middle Caspian Sea was represented by 13 taxa and consisted mainly of non-indigenous species typical of the Palearctic region. Native fauna was represented by three species—cladoceran Evadne anonyx, Podonevadne camptonyx, and copepod Halicyclops sarsi during the study period. The quantitative variables of zooplankton did not reach a high level in May 2020 and 2021 compared to the data of previous years. Cladocerans Podonevadne camptonyx, copepods Acartia tonsa, and larvae of Cirripedia dominated in 2020. By 2021, the dominant species of last year had been replaced by the cladoceran Evadne nordmanni. One-way ANOVA analysis detected significant differences in the quantitative variables of cladocerans and copepods between different years of zooplankton study. The decreasing abundance, biomass, and alteration of the dominant zooplankton species in the Middle Caspian Sea during the study period may be associated with the feeding type of predator species and a slight elevation of water salinity.

The northern section of the Caspian Sea and lower reaches of the Zhaiyk (Ural) River is an important fishery for Kazakhstan. In the present study, a total of 1597 individuals of ten fish species were analysed. The fish were caught over three years, from 2018 to 2020. For each species studied – Abramis brama, Alosa saposchnikowii, Atherina boyeri caspia, Carassius gibelio, Chelon auratus, Cyprinus carpio, Leuciscus aspius, Rutilus caspius, Sander marinus and Sander volgensis – between 100 and 200 individuals were examined. A series of generalized linear models (GLMs) were used to examine the association between individual parasite intensity of infection and the Fulton index, age, year the fish was captured, where the fish was captured (northern Caspian or Zhaiyk River) and sex. For each GLM, the best-fitting probability distribution was used –either Poisson, zero-inflated Poisson, negative binomial or zero-inflated negative binomial. For some fish/parasite species, an increased Fulton index was associated with higher intensities of parasite infection, whilst, for others, the Fulton index decreased with the intensity of parasite infection. This was also true of age-related intensity of infection, with some parasites having an increased intensity of infection with age whilst others had a decreased intensity of infection with age. There was also some evidence of variation in intensity of parasite infection between different years when the fish were caught. For some species of fish that are endemic to both the fresh waters of the Zhaiyk River and the low-saline waters of the northern Caspian, there were variations in intensity of parasite infection between the two environments. The best-fitting probability distribution also gave some information about the dynamics of infection. No fish species had a Poisson distribution of parasites, which is consistent with an entirely random infection process, with all fish being potentially exposed. For some parasites, the distribution was a zero-inflated Poisson, which is consistent with either the fish being exposed to parasite infection or not; and, if exposed, infection was a random process. Other parasites had a negative binomial distribution, consistent with the entire fish population being exposed, but the infection process was clumped or there were variations in the susceptibility of infection between fish. Finally, some of the parasites had a zero-inflated negative binomial distribution, which can be interpreted as part of the fish population not being exposed and the remainder of the population being exposed to a clumped or aggregated infection process and/or a variation in individual susceptibility to infection.

Паразитические организмы, являясь неотъемлемой частью природных и техногенно-трансформированных экосистем могут служить в качестве индикаторных видов, которые отражают воздействие на окружающую среду, реагирующие на изменения среды обитания с изменениями в физиологии или химическом составе. Эктопаразиты, в силу того что могут взаимодействовать с окружающей средой различными способами способны предоставлять информацию о гидро- и геохимическом фоне окружающей среды благодаря присутствию или отсутствию. Эндопаразиты, в свою очередь, менее подвержены воздействию токсичных веществ, демонстрируя способность аккумулировать токсикантов окружающей среды внутри своих тканей. Состояние окружающей среды оказывает значительное влияние на паразитов, определяющие их количественные и качественные показатели структуры популяции. В связи с этим создается необходимость проведения планомерных мониторинговых ихтиопаразитологических исследований в водоемах Северного Казахстана, используя паразитов рыб как индикаторных видов. В статье приведены данные проведенных ихтиопаразитологических исследований в водоемах Северного Казахстана (Акмолинская, Павлодарская и Северо-Казахстанская области), в результате которого установлено 23 видов паразитических организмов, в том числе 1 вид зоонозного (Raphidascaris acus) и 2 вида высоковирулентных (Gyrodactylus cyprini, Schyzocotyle acheilognathi) гельминтов. Для водоемов Северного Казахстана впервые установлены Gyrodactylus cyprini, Gyrodactylus cernuae, Eudiplozoon sp., Diplostomum paraspathaceum, Diplostomum chomatophorum. Затон Черноярский бассейна Иртыш можно считать неблагополучным по эргазилезному паразитозу.

In the Karkary-Kegen valley of the Almaty region of Kazakhstan, when breeding a new breed of sheep with the participation of different animal species, their parasitofauna was formed from parasites present in this biocenosis or natural focus. In this region there were 75 species of parasites belonging to 5 types, 5 classes, 3 subclasses, 3 orders, 10 suborders, 4 superfamilies, 21 families, 11 subfamilies, 1 tribe and 34 genera. During the formation of the breed for more than 20 years, archaromerinos had 28 species of parasites: one species of trematodes (D.lanceatum,), 4 species of cestodes (T.hydatigena, larvae; E.granulosa,larvae; M.expansa; M.benedeni) and 23 species of nematodes (S.ovis, Ch.ovina, T.axei, T.colubriformis, O.circumcincta, O.occidentalis, O.trifida, O.trifurcata, M.marshalli, N.archari, N.dogieli, N.filicollis, N.oiratianus, N.spathiger, N.longissimespiculata, D.filaria, P.davtiani, P.hobmaieri, P.raillieti,P.skrjabini, C.nigrescens, B.schulzi, T.skrjabini). In the next 60 years, hybrids acquired another 35 species. Thus, a new breed of animals is included in the cycle of invasion in the biocenosis. Some parasites (not previously noted in this biocenosis) that are in the body of archaromerinos, getting into the external environment with feces, form new foci, involving other species of animals living in this biocenosis in the circulation.