Tests of host competence
Standard length of each fish was measured, and then a single fish was stocked in a tank with 0.5 L of dechlorinated tap water. Gyrodactylids were collected from heavily infected goldfish and two worms were transferred to the caudal fin of each fish anaesthetized with MS-222 as described by King and Cable (2007). Following 5 min inoculation, the caudal fins of 30 individuals of each species were examined using a stereomicroscope. On day 1 and day 7, gyrodactylids were examined on caudal fins of these fish anaesthetized with MS-222. If a fish was infected with at least one gyrodactylid on day 1 and three gyrodactylids on day 7, it was recorded as attachment success and establishment success, respectively, which was modified from King and Cable (2007). Attachment and establishment success rates were calculated as the number of infected fish divided by the number of exposed fish on day 1 and day 7, respectively. Mean abundance, the mean number of parasites per fish, infected or not, also was calculated after establishment. If establishment success rate and mean abundance were significantly lower than those on the goldfish in the control group, the species was considered as a low competent host, whereas any species without any establishment success was defined as an incompetent host.