Description of Gyrodactylus banmae n. sp. (Monogenea, Gyrodactylidae) parasitic on zebrafish, Danio rerio.

A new species of Gyrodactylus was described on the body surface of zebrafish (Danio rerio) in China. Basing on morphological characteristics and ITS sequence, we identified the parasite as a new member of the Gyrodactylus-wageneri group. Morphologically, Gyrodactylus sp. nov. is greatly similar to "G. zebrae", another species parasitic on zebrafish: both have moderately stout hamulus, marginal hook sickle with a prominent heel and toe, as well as a curved blade. However, distinct haptoral shape differences were detected between these two species. The dorsal bar is straight in Gyrodactylus sp. nov. but strongly curved in "G. zebrae", and the sickle shaft in Gyrodactylus sp. nov. is approximately perpendicular to the base, but in "G. zebrae" it is slanted downwards. The ITS1-5.8S-ITS2 sequence also indicate that Gyrodactylus sp. nov. exhibits the highest similarity to "G. zebrae": 95.7% sequence identity suggests interspecific differentiation. Phylogenetic analysis of the ITS1-ITS2 sequence showed that Gyrodactylus sp. nov. formed a sister clade with "G. zebrae", and exhibited a relatively close phylogenetic relationship with G. kobayashii, G. gurleyi, and G. longoacuminatus, all of which parasitise on goldfish, Carassius auratus. To test the susceptibility of zebrafish and goldfish to the Gyrodactylus sp. nov., ten gyrodactylids were inoculated to the caudal fin of zebrafish and goldfish. The gyrodactylids exhibited the ability to attach themselves to the goldfish, and some gyrodactylids reproduced a few days after the inoculation. On day 9, however, the mean abundance sharply decreased to zero on goldfish and increased to more than 30 on zebrafish. The result suggested that golfish is an unsuitable host for Gyrodactylus sp. nov. Therefore, on the basis of morphology, molecular sequence similarity, and host susceptibility, we conclude that the gyrodactylid found on the zebrafish is a new species, which we named Gyrodactylus banmae.