Argulus foliaceus (Crustacea: Branchiura) infestation in common carp (Cyprinus carpio) from South Sulawesi, Indonesia.

Parasites represent a major constraint in pond-based aquaculture, as their presence can lead to substantial fish mortality and associated economic losses. This study investigated the extent of Argulus infestation in cultured common carp (Cyprinus carpio) reared in a freshwater hatchery in South Sulawesi Province, Indonesia. Two host groups were examined: broodstock (n = 60; 1091.2 ± 58.16 g) and fingerlings (n = 150; 19.6 ± 0.82 g). Identification of Argulus specimens was conducted using morphological examination complemented by molecular analyses. Parasite prevalence and mean intensity were quantified, and Spearman's rank correlation was applied to determine the relationship between fish body weight and infestation severity. Both morphological and molecular evidence confirmed that the Argulus specimens infesting carp in this study were Argulus foliaceus. Fish body weight was significantly correlated with infestation intensity (P < 0.01), with broodstock exhibiting markedly higher prevalence and mean intensity than fingerlings. Preferred attachment sites differed between life stages: the base of the pectoral fins in broodstock and the body surface in fingerlings. These findings indicate that host life stage and body size strongly influence the severity and spatial pattern of A. foliaceus infestations in common carp. The outcomes provide a scientific basis for developing management guidelines to reduce the incidence and spread of Argulus in aquaculture systems.