First record of Neobenedenia girellae (Monogenea: Capsalidae) as the cause of mortality of yellow snappers, Lutjanus argentiventris , farmed in artisanal cages in the Urías Estuary, Mazatlán, Mexico

Summary A parasitic outbreak of capsalid monogeneans occurred in May 2023 in artisanal cages where yellow snappers ( Lutjanus argentiventris ) are farmed. Cages are set at the entrance to the Urías Estuary in Mazatlán, northwestern Mexico. The outbreak resulted in the loss of 8,890 fish from an initial stock of 10,000. Twenty fish specimens were examined to determine the cause of death. Massive tissue damage was observed in the hosts’ skin, and a severe infection with capsalid monogeneans was detected. The capsalid was initially identified morphologically as a member of the genus Neobenedenia ; however, due to long-standing taxonomic confusion between N. girellae and N. melleni , we further corroborated the identification using ribosomal (28S rRNA) and mitochondrial (cytb) DNA sequences, analyzing sequence divergence values and phylogenetic interrelationships. Photomicrographs of processed specimens, as well as scanning electron photomicrographs, were obtained. The monogenean was identified as Neobenedenia girellae and is reported for the first time as a parasite of farmed L. argentiventris . The monogenean reached very high infection levels, with a prevalence of 100 ¢ %, and a mean intensity of 68.2 parasites per infected host. To more accurately describe the effect of this highly pathogenic monogenean on the host, we assessed the body condition factor of the hosts (1.22 ± 0.05). We compared it with the standard value reported in the literature.