Fig 1. Mean abundance of Gyrodactylus kobayashii on fins of goldfish (Carassius auratus ,) and silver crucian carp (C. auratus gibelio ,) in different combinations of fishes. Control group, 10 C. auratus ; TG1, 10 C. auratus + 10 C. auratus gibelio ; TG2, 10 C. auratus + 10 grass carp (Ctenopharyngodon idellus ); TG3, 10 C. auratus + 10 swordtail (Xiphophorus helleri ); TG4, 10 C. auratus + 3 C. auratus gibelio + 4C. idellus + 3 X. helleri . Different letters on the grey bar indicate a significant difference in mean abundance among the five groups at 0.05 level.

Fig 2. Effects of additional fish species on average speed (A), average adjacency distance (B) and cumulative contact time (C) among six goldfish (Carassius auratus ). Different letters on the grey bar indicate a significant difference among the four groups at 0.05 level.

Fig 3. Trajectory heatmap of a goldfish (Carassius auratus ) within ten minutes in goldfish (as control), silver crucian carp (Carassius auratus gibelio ), grass carp (Ctenopharyngodon idellus ) and swordtail (Xiphophorus helleri ) groups. The warmer color on the right side of heatmap indicates much more time the goldfish stayed there.

Fig 4. Conceptual model of spatial distribution of fish with schooling behavior. (A) School of goldfish (Carassius auratus ) (orange); (B) Goldfish school mixed with silver crucian carp (Carassius auratus gibelio ) (grey) with low competence, reducing encounters between infected and uninfected goldfish; (C) Goldfish school separated from incompetent grass carp (Ctenopharyngodon idellus ) or swordtail (Xiphophorus helleri ) (green) , hardly reducing encounters between infected and uninfected goldfish.

S Video. Relationship of fish schools between focal host and added fish species. (A) Schooling patterns of goldfish (Carassius auratus ) alone; (B) Schooling patterns of goldfish and silver crucian carp (Carassius auratus gibelio ); (C) Schooling patterns of goldfish and swordtail (Xiphophorus helleri ); (D) Schooling patterns of goldfish and grass carp (Ctenopharyngodon idellus ).