Dynamics of Dibothriocephalus spp. infection in fish from the Shardara Reservoir (Republic of Kazakhstan) and fish decontamination by freezing method

The study aimed to investigate the infestation of commercial fish species in the Shardara Dam with Dibothriocephalus spp. plerocercoids, the localization of plerocercoids within fish bodies, and the effect of freezing treatment on plerocercoid mobility. The study was conducted from 2021 to 2024 in the area of the Shardara Dam, located on the Syr Darya River in the Turkistan Region, Kazakhstan. A total of 993 fish specimens were examined for the presence of Dibothriocephalus spp. plerocercoids. The fish belonged to four species: common perch (Perca fluviatilis L.), wels catfish (Silurus glanis L.), pikeperch (Sander lucioperca L.), and northern pike (Esox lucius L.). An experiment on fish decontamination was performed using freezing temperatures of - 8 °C, - 10 °C, - 12 °C, and - 14 °C. Fish specimens weighing up to 2.5 kg were used. The condition of the plerocercoids was assessed after 24, 48, 72, and 96 h. In this study, the northern pike demonstrated the highest infestation rates. The extensity of infestation in the northern pike, the extensity ranged from 45% to 57.1%, with an average of 50.4%, depending on the year and sampling location. A high intensity of Dibothriocephalus spp. plerocercoid invasion was observed in the muscle tissue and edible internal organs. Freezing fish at - 12 °C for at least 96 h or at - 14 °C for at least 48 h effectively inactivates Dibothriocephalus spp. larvae. The study identified a persistent focus of dibothriocephalosis in the area of the Shardara Dam. In accordance with the legislation of the Republic of Kazakhstan, fish caught in the reservoir must undergo mandatory decontamination.