DOI: 10.5061/dryad.5x69p8d0p
title: A survey of gyrodactylid parasites on the fins of Homatula variegata in central China

description: 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 (&lt;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 (&lt;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.
description: Ethical Note This study was approved by the
 Animal Care and Use Committee of Shaanxi Normal University.
 Study area and sample collection The fish
 (Homatula variegata) were collected (n = 442) with seine nets from late
 March to late September 2016 in Xunyangba (33.33°N, 108.33°E), Ningshan,
 County located on the southern slopes of the Qinling Mountains in Shaanxi
 Province, central China. The water temperatures on the collection days
 were recorded (Table 1). Each fish was individually placed in a plastic
 tank filled with filtered river water and was transported to a field
 laboratory and examined within one hour. The fish were euthanized with
 excessive eugenol anesthetic fluid and fixed with 5-10% formalin. The
 total length of each fish was recorded, and the fins were examined for the
 presence of parasites that were removed and immediately identified on
 temporary wet mounts. These two species of Gyrodactylus were found under a
 dissecting microscope (OLYMPUS, SZ61, 45X), Then they were placed on glass
 slides that had drops of glycerin-water with pointed ophthalmic forceps.
 If there was a cap-like bone piece structure covering the base of the
 central hook, then it was recorded as Paragyrodactylus variegatus;
 otherwise, it was recorded as Gyrodactylus sp. The parasites were stored
 in formalin. Almost all the parasites stuck to the skin after
 immobilization. Voucher specimens of the parasites and host were deposited
 in the Fish Disease Laboratory, Shaanxi Normal University (Accession
 number: H. variegata: Acc.HV20160012; Gyrodactylus sp.: Acc.GS20160001 and
 P. variegatus: Acc.PV20160001). Analysis of parasite
 location The different numbers of parasites on each fin
 corresponding to different fish body lengths were examined, from March to
 September, 2016. The parasite species and location of parasites on the
 host’s fins were examined by using a two-way ANOVA, with the number of
 parasites on different fins used as the dependent variable. The
 microhabitat occurrence for each gyrodactylid species was determined by
 observing its position on the fins. The distributions of each gyrodactylid
 species on each of the different fins were compared by two-way ANOVA with
 multiple comparisons (Tukey's HSD test) to assess the significance of
 the difference. The significance level was set at p &lt; 0.05.
 Relationships between water temperature, parasite load location and fish
 size To test for the overall effects of water temperature and fish body
 length on the distribution of the number of parasites on the host fins, a
 generalized linear model (GLM) was also built using water temperature or
 fish body length as predictors. To further explore the relationships of
 fish size (length) and water temperature with the number of parasites on
 different fins, Spearman correlation statistical analysis was
 applied.