An infection of Gyrodactylus kobayashii Hukuda, 1940 (Monogenea) associated with the mortality of goldfish (Carassius auratus) from central China.

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Goldfish, Carassius auratus, widely distributed across Eurasia, is one of the earliest fish domesticated for ornamental purposes. A series of diseases break out due to high-density culture of goldfish, causing significant economic losses. Here, we report for the first time an infection of Gyrodactylus kobayashii associated with the high mortality of goldfish from a fish farm in Anziying township of Henan province, China, following their transfer to several aquariums. In the first 2 weeks after goldfish (n = 4200, weight 10.24 ± 1.45 g) transfer to aquariums, a total of 3335 goldfish were lost, representing 79.4 % of the initial stocked biomass. The examination showed that no other pathogens were found in this batch of fishes, except for G. kobayashii. The high burdens of G. kobayashii/fish (264.7, range 100-450) were the primary reason for the high mortality, although this was not the sole cause. In addition, the isolate of G. kobayashii from goldfish (C. auratus) in Henan province of central China was described. The morphological characterization was performed using morphometric measurements and drawings of opisthaptoral hard parts of the parasites. The molecular description was performed based on phylogenetic analysis of a reference DNA sequence spanning 5.8S and ITS-2. Importantly, the present study provides for the first time a full 25 point-to-point morphometric measurements and high-resolution images of attachment organ of G. kobayashii.