First record of Camallanus cotti (Fujita, 1927) in traded guppies (Poecilia reticulata) from India

The guppy Poecilia reticulata is a widely traded ornamental fish species, valued for its popularity in aquariums globally. Parasitic infections pose a significant threat to both ornamental culture and native fish populations. This study records the first occurrence of the intestinal nematode Camallanus cotti (Fujita, 1927) in guppies from India, confirmed through both morphological and molecular analysis. Sixteen guppies were collected from the Kolathur ornamental fish market, Chennai, Tamil Nadu. Examination revealed that 11 fish (68.75%) were infected with red thread-like nematodes protruding from the anus. A total of 41 worms were recovered, with a mean intensity of 3.73 and a mean abundance of 2.56 worms per fish. Light microscopy confirmed diagnostic features of C. cotti, including the robust cephalic capsule and scanning electron microscopy illustrates the attachment of the parasite to intestinal wall. Molecular characterization using 18 S rRNA gene sequencing (GenBank Accession PX446961.1) showed 99.84% similarity with reference sequences, validating the morphological identification. Infected guppies exhibited visible clinical signs, including abdominal distension and threadlike worms protruding from the anus. The findings highlight the risk posed by C. cotti to ornamental fish health and emphasize the importance of quarantine, monitoring, and surveillance to prevent its spread through the aquarium trade.