Morphometric and molecular identification of Argulus japonicus (Thiele 1900) in vulnerable Himalayan snow trout, Schizothorax richardsonii (Gray 1832)

Abstract

Argulus is a crustacean branchiuran parasite that causes severe problems in aquacul-ture throughout the world. Conventionally, Argulus spp. are identified through the morphological descriptions. In the recent years, polymerase chain reaction amplifica-tion with nuclear ribosomal RNA sequence coupled with morphological description is becoming standard for the species- level identification of Argulus spp. The present study investigated Argulus sp. in snow trout, Schizothorax richardsonii, using morpho-logical and molecular tools. Morphologically, the parasite had branched dorsal ridges of the carapace, clubbed shaped anterior respiratory area, curved shaped posterior respiratory area, three relative sharp teeth and chitinous shovel peg on the fourth swimming appendages. Females Argulus sp. were larger in size than males in their length and width. Morphological characteristics and 18s rRNA study revealed that the parasite species was Argulus japonicus. A phylogenetic tree was constructed to examine relationships between these A. japonicus sequences and existing archived se-quences. The maximum distribution of pathogenic argulid was observed in the dorsal fin, followed by the ventral fin and pectoral fin. The present study contributes to the first species- level morphological and molecular identification of A. japonicus in vulner-able Himalayan snow trout, S. richardsonii.