Study subjects and housing
We used a wild population of threespine stickleback, Gasterosteus
aculeatus , caught with unbaited minnow traps from a vegetated
freshwater lake in April 2021 (Syðridalsvatn, 66° 7’ N, 23° 14’ W).
Thirty-three fish of the size 4.0-4.1cm were transported the short
distance to the laboratory (<15min). This size of fish most
likely represents individuals that hatched in spring/summer 2019. All
fish were placed in individual holding tanks of 9.5l (Aquaneering.com).
Each tank was equipped with a single 12cm knee-shaped PVC pipe for
cover. Temperature was kept at 12.0°C, with an 8:16 h light/dark cycle
regime. The tanks were continuous flow through, fitted with a biological
filter, UV sterilization and aerated. After a single day of acclimating
to the laboratory we began observations. Fish were fed defrosted frozen
bloodworms (Chironomus spp .) on the day of capture and then to
satiation daily after the experiment. Behavioral experiment without
invasive or stressful procedures, such as the current experiment, do not
require licensing by Icelandic law.