Behavioral traits including shoaling, activity, feeding rate and
food consumption were assayed 7 d after the start of the exposure.
Each behavioral trial was initiated with the random selection of
one of the exposure aquariums. For shoaling and activity, the apparatus
and protocol used was modified from the one proposed by
Moretz et al. (2007). The experimental arena was an aquarium
(30 cm high 30 cm wide 60 cm long) filled with the exposure
concentration of sertraline for treated fish, or no sertraline for control
fish to a depth of 14 cm. This aquarium was divided lengthwise
into three compartments (two small, 15 cm, and one large central
compartment, 30 cm) separated by two transparent glass partitions.
The partitions allowed visual, but not physical or olfactory
interaction, between the shoal and the focal individual, while black
curtains covered the outer sides of the aquarium. A parallel and a
vertical line to partitions drawn on the bottom divided the central
compartment into left/right parts and forward/backward parts,
respectively (Fig. S1). A shoal of four similar-sized fish was introduced
into one of the smaller compartments 1 h before the start
of the experiment. After 1 h, the test was started by introducing
a single fish to the center of the large compartment. It was allowed
to acclimate for 5 min, followed by a 600-s video recording of its
movements from above. To obtain a quantitative measure of shoaling,
the number of times the fish crossed the parallel line and the
duration of time it spent opposite to the shoal were recorded.
Simultaneously with shoaling, activity was recorded as the number
of both parallel and vertical lines crossed in 600 s.