Results
The control goldfish group had 100% establishment success and a mean
abundance of 17.0 ± 13.2. Of the 12 fish species, 8 were infected byG. kobayashii with 6.7-83.3% attachment success (Table 1). But
only C. auratus gibelio became infected with 56.7% establishment
success and 3.0 ± 4.4 mean abundance (Table 1), which were both
significantly lower than those on the control group (P< 0.05). The silver crucian carp is defined as a
low-competence host, while the other species with no establishment
success are considered as incompetent hosts.
In the mixed-species culture, no G. kobayashii was detected on
grass carp and swordtail (Fig 1). Compared with the goldfish in the
control group (85.8 ± 25.1), the mean abundance of G. kobayashiion fins of goldfish was lower in the swordtail group (70.0 ± 22.2), the
multi-species group (75.9 ± 30.8) and the silver crucian carp group
(30.0 ± 16.5), but higher in the grass carp group (116.1 ± 33.2) (Table
2). There were significant differences in mean abundance on goldfish
between the silver crucian carp group and all other groups (P< 0.05) (Fig 1). Mean abundance of G. kobayashii onC. auratus gibelio in the silver crucian carp group (7.1 ± 5.6,
66.0% prevalence) and the multi-species group (10.9 ± 3.8, 86.7%
prevalence) were both significantly lower than that on C. auratusin the corresponding group (P < 0.05). Total population
size of G. kobayashii was 857.8, 370.4, 1160.8, 698.8 and 791.4
in the five groups, respectively. At the host community level, the mean
abundance was 18.5 (± 10.7) and 39.6 (± 15.1) in the silver crucian carp
and the multi-species groups, respectively (Table 2). A significant
difference in total mean abundance on all hosts was detected between the
control group and the silver crucian carp group (P <
0.05) and the multi-species group (P < 0.05).
Observation of schooling patterns showed that population of goldfish
mixed well with the silver crucian carp, but not with the grass carp and
the swordtail (S Video). The average adjacency distance among goldfish
significantly increased, while the average speed and cumulative contact
time significantly decreased in all mixed groups when compared with
those in control group (P < 0.05) (Fig 2). The
trajectory heatmap showed that the goldfish tended to school along the
tank wall both in the control and silver crucian carp groups. In
contrast, goldfish were uniformly distributed in the whole tank in the
grass carp group and in part of the tank in the swordtail group (Fig 3).
A schematic model of the spatial distribution of the fishes under the
different experimental conditions is presented in Fig 4, with the school
of goldfish alone (Fig 4A), the goldfish school mixed with
low-competence silver crucian carp (Fig 4B), and goldfish schooling
separately from incompetent grass carp (Fig 4C).