First taxonomic description of a gyrodactylid, Gyrodactylus cichlidarum Paperna, 1968 (Monogenoidea) infecting Nile tilapia, Oreochromis niloticus (Linnaeus, 1758) (Cichlidae) in the United States

Abstract

The parasites of Nile tilapia, Oreochromis niloticus (Linnaeus, 1758) (Cichliformes: Cichlidae) are poorly documented in the U.S. Gyrodactylids can be pathogens of cultured and wild fish populations and their infections can be relevant to the captive maintenance of fishes as well as wild fish health monitoring programs. As part of a survey of the parasites of Nile tilapia cultured within high density flow-through raceways (hydrologically linked to Sougahatchee Creek, Tallapoosa River), we observed numerous specimens of Gyrodactylus cichlidarum Paperna, 1968 (38% prevalence; 2.5 mean intensity) attached to the skin, fins, and gill filaments. This parasite was originally described from the skin and gill of mango tilapia, Sarotherodon galilaeus (Linnaeus, 1758) (Cichlidae) from pools and streams in the Accra Plains, Ghana. Live specimens of G. cichlidarum intended for morphology were heat-killed, formalin-fixed, routinely stained, cleared, and whole-mounted on glass slides. Additional specimens were preserved in 95% ethanol for DNA extraction and sequencing of the internal transcribed spacers 1 and 2 (ITS1, ITS2) and the 5.8S ribosomal DNA. We identified our specimens as G. cichlidarum by having a ventral bar with a distinctive dorsal posteromedial knob and marginal hooks that have a wide aperture and flat sickle base. Our two identical sequences of the ITS1-5.8S-ITS2 differed from a sequence of G. cichlidarum from the United Kingdom by 1 bp. Although this parasite was mentioned in a vaccine study of Nile tilapia in the U.S. in 2011, the present study is the first to diagnose the morphology of G. cichlidarum infecting Nile tilapia in the U.S. (and thereby also the first to deposit whole-mounted voucher specimens of G. cichlidarum from this host and locality). The present study also provides the first nucleotide sequences tethered to a morphological voucher of G. cichlidarum in the U.S., and these resulting sequences were included in a phylogenetic analysis.