Aquarium experiment and sampling
For the aquarium experiment, we examined two mock fish communities of Hemigrammocypris neglectus , Candidia temminckii ,Oryzias latipes , Rhinogobius flumineus , andMisgurnus anguillicaudatus . Mock community 1 (MC1) consisted of one individual of each of the five fish species, whereas mock community 2 (MC2) consisted of three H. neglectus individuals and one of each of the other four fish species (Figure 1). We used two aquaria (A and B). Each aquarium was used four times, twice for each mock community, giving two replicates (R1 and R2). This resulted in eight experimental units (2 mock fish communities × 2 aquaria × 2 replicates). Figure 1 shows the experimental setup used in this study.
To set up the aquaria, we added 20 L of tap water into the two aquaria (GEX Co. Ltd., Osaka, Japan) and heated the water with a heater (Spectrum Brands, Wisconsin, US) until the water temperature reached 25°C. Water in the two aquaria was maintained at 25°C and constantly circulated with an aeration device. Before adding fish to the aquaria, water was sampled for the negative control. The first samples (Day 0) were taken an hour after adding the fish. Following this, samples was taken each day until Day 4. At sampling, two 1-L samples of surface water were collected from each aquarium. After each sample was taken, 2 L of tap water was added to each aquarium to maintain the volume of water. Fish were not fed during the 4 days. The weight of individual fish species was measured using an electronic balance immediately after the last sampling. After that, the two aquaria were bleached before being reused.