Cryptosporidium spp. and Eimeria spp. (Apicomplexa: Eimeriorina) of freshwater Cyprinid fish species in the Kura River basin in Azerbaijan territory

This study aims to determine the prevalence of Cryptosporidium and Eimeria spp. oocysts in fish specimens in the river Kura (Azerbaijan). It was conducted during the 2021–2022 at two sites: Mingachevir reservoir in central Azerbaijan and in Neftchala district where the river finally enters the Caspian Sea through a delta of the Kura River estuary. The diagnosis was performed microscopically. Fine smears from the intestine epithelial layers stained by the specific modified acid-fast staining method (Ziehl-Neelsen) for Cryptosporidium oocysts. To identify Eimeria oocysts, each fish's faecal material and intestinal scrapings were examined directly under a light microscope in wet samples on glass slides with a coverslip. Results revealed a prevalence of Cryptosporidium and Eimeria species infections in fish hosts from both territories Rutilus caspicus, Alburnus filippi, Abramis brama orientalis and Carassius gibelio. Of 170 investigated fish specimens, 8.8% (15/170) were infected with Cryptosporidium species oocysts. Eimeria species oocysts were identified in 20.6% (35/170). The presence of Cryptosporidium and Eimeria infections in fish specimens are natural infections. However, their presence in fish species may be attributed to the age of the fish species and water pollution. This is the first regarding the prevalence of Cryptosporidium oocysts in fish species in the study area.