Effects of additional fish on schooling behavior of goldfish
To determine changes of goldfish swimming behavior in the presence of
other fish species , the ectoparasite-free fish were randomly assigned
to four groups, including the control group (12 goldfish), the silver
crucian carp group (6 goldfish and 6 silver crucian carp), the grass
carp group (6 goldfish and 6 grass carp), and the swordtail group (6
goldfish and 6 swordtail). Each group was replicated ten times and
maintained in a square tank (67×44×33 cm) containing 50-L dechlorinated
tap water with a minimum of 5 mg/L dissolved oxygen at 20 ± 1 °C. A web
camera (BASLER, acA1920-155uc, 25 frames/s) was placed over each fish
tank at a 1.5 m distance. Behavior of the fish in each tank was recorded
continuously for 10 min. Average speed, average adjacency distance and
cumulative contact time (less than 1 cm distance between two goldfish)
among the six goldfish in each tank were calculated from the videos
using the program Ethovision XT10.0 (Noldus, Netherlands). Trajectory
heatmap of a randomly selected goldfish was also generated from the
videos using the software Ethovision.