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

Citation

Chen, Xiaoning; You, Ping; Wang, Biao; Nie, Jianzhen (2020), A survey of gyrodactylid parasites on the fins of Homatula variegata in central China, Dryad, Dataset, https://doi.org/10.5061/dryad.5x69p8d0p

Abstract

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 Pvariegatus occurring more frequently on caudal fins. However, Gyrodactylus sp. appeared to occur on fish of all lengths, while Pvariegatus 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.

Methods

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 < 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.

Funding

National Natural Science Foundation of China, Award: 31872203

Natural Science Foundation of Shaanxi Province, Award: 2017JM3014