Parasite Fauna and Infection Patterns in Cyprinus carpio L. from Lake Systems of the Amu Darya Delta: a Comparison Across Host Age-season Groups

Ongoing hydroecological transformation of water bodies in the Aral Sea basin has created conditions under which fish parasites serve simultaneously as sensitive bioindicators of ecosystem status and as epizootiological agents capable of undermining the resilience of commercially important fish populations.This study assessed the parasite fauna and infection dynamics of common carp (Cyprinus carpio L.) and wild carp (sazan) from lake systems of the Amu Darya delta, Karakalpakstan, Uzbekistan, with a descriptive comparison of prevalence and intensity of infection across four combined host-age-season groups.A total of 180 fish specimens -yearlings and 3-year-olds -were examined by complete ichthyoparasitological dissection across multiple seasons during 2015-2020, with age classes verified using a separate, non-lethal (partial) subsample of 19 fish.Eight parasite taxa were recorded, spanning six major groups: Protozoa (Chilodonella cyprini Moroff, 1902 (syn.C. piscicola), Ichthyophthirius multifiliis), Monogenea (Dactylogyrus extensus, Gyrodactylus medius), Cestoda (Bothriocephalus acheilognathi Yamaguti 1934; syn.B. opsariichthydis), Digenea (Diplostomum spathaceum), Nematoda (Capillaria tomentosa), and Copepoda (Lernaea elegans).Maximum parasite species richness was observed in yearling sazan during May-July, when all six taxonomic groups were concurrently recorded and mean prevalence across registered taxa reached 12.1 %.In contrast, autumnwinter groups showed reduced taxonomic diversity, though ectoparasites and monogeneans persisted at epidemiologically significant levels, particularly in 3-year-old carp where Chilodonella cyprini prevalence reached 24 %.These descriptive findings are consistent with the broader literature suggesting that parasite communities may serve as indicators of ecosystem condition, although this study did not include direct hydrochemical measurements, and they underscore the potential value of age-stratified, seasonally differentiated parasitological surveillance integrated with future hydrochemical monitoring in this ecologically sensitive region.