A survey of gyrodactylid parasites on the fins of Homatula variegata in central China

In this study, two parasites on the fins of Homatula variegata were recorded from March to September 2016. A dissection mirror was used to examine the distribution and quantity of the ectoparasitic Gyrodactylus sp. and Paragyrodactylus variegatus on the host Homatula variegata in different seasons. The present study explored possible explanations for the site specificity of gyrodactylid parasites in 442 Homatula variegata infected with 4307 Gyrodactylus sp. (species identification is incomplete, only characterized to the genus level) and 1712 Paragyrodactylus variegatus. These two gyrodactylid parasites were collected from fish fins, and the fish were harvested in China's Qinling Mountains.The results indicated that the highest number of Gyrodactylus sp., which was numerically the dominant species, appeared on the fish fins in April, while the highest number of Paragyrodactylus variegatus was found on the fish fins in March. The two parasite species appeared to be partitioned spatially, with Gyrodactylus sp. occurring more frequently on pectoral and pelvic fins, and P. variegatus occurring more frequently on caudal fins. However, Gyrodactylus sp. appeared to occur on fish of all lengths, while P. variegatus tended to occur more abundantly on shorter fish rather than on longer fish. At lower Gyrodactylus sp. infection levels (<100), the pelvic and pectoral fins were the main locations of attachment, followed by the dorsal fin. For infections of more than 100 parasites, more samples of Gyrodactylus sp. were located on the pectoral fin. For a low number of Paragyrodactylus variegatus infections (<100), the pelvic and pectoral fins were the preferred locations of attachment, followed by the caudal fin. Between April and September, there were many monogenean parasites on fish fins, and the fish size was within the range of 5–10 cm. However, when a fish was longer than 10 cm long, the number of parasites on its fins greatly decreased.