Retrospective analysis and current trends in the disease incidence of commercial fish species in the water bodies of the Irtysh River basin (Kazakhstan, Central Asia)

Abstract

The fishery sector in Kazakhstan plays a vital role in ensuring the country's food security. However, the industry faces challenges related to infectious and parasitic diseases in fish, which reduce the productivity of water bodies and degrade fish quality. Therefore, ichthyopathological research remains a relevant issue. One of the key monitoring areas is the Irtysh River Basin in East-ern Kazakhstan, a significant ecosystem with a developed ichthyofauna and an active fishing indus-try.

The aim of this study was to analyze the prevalence of parasitic and infectious diseases in fish from the water bodies of the Irtysh River Basin based on long-term monitoring data.

The analysis is based on ichthyological, parasitological, and virological observation data collected from the Bukhtyrma, Shulbinsk, Ust-Kamenogorsk reservoirs, Lake Zhaisankol, the reser-voirs of the Kanisha Satpaev canal, and the Irtysh River from the 1970s to 2024. Disease incidence was assessed based on invasion intensity, species composition of infected fish, and geographical distribution.

Persistent disease foci affecting fish populations were identified. From 1970 to 2024, three key diseases were recorded: dermatofibrosarcoma in pikeperch (with a peaking at up to 57% in 1980-1983), ligulosis and digrammosis in carp (up to 50% in 1980 and 35% in 2012, respectively). In recent years, disease incidence has decreased. The detection of Opisthorchis spp. was not ac-companied by identification of intermediate hosts, reducing the risk of opisthorchiasis. A favorable epizootiological situation regarding particularly dangerous viral diseases, such as carp spring viremia and infectious hematopoietic necrosis, was observed in all studied water bodies. The obtained data confirm the cyclical and unpredictable nature of fish diseases, highlighting the need for continuous monitoring.