Study animals and husbandry
All shrimp used were from a captive-bred colony sourced from the aquarium pet trade and subsequently maintained in the Freshwater Laboratory of the Animal Facility in Penryn, Cornwall. On arrival in the laboratory, adult shrimp were housed in large breeding stock tanks (28cm x 19.5cm x 18.5cm) for several months to establish the breeding colony. Behavioural data for this study were collected during October and November 2022 under the local ethical approval (University of Exeter approval ID 517031). Forty-eight individuals were taken from stock tanks and moved to individual housing containers (22cm x 8.5cm x 15cm) connected to a shared recirculating water supply. Each individual tank contained a short piece of black plastic (3.5cm x 3.5cm) and a plastic plant to provide refuge. Shrimp moved to these containers were sampled haphazardly from stock, but with the condition that they needed to have a body length of at least 6mm. These were presumed to be adult females and males since individuals with a total length of >7mm can be sexed ensure the effective tracking of behaviour in the experimental set-up (described below). Water temperature was maintained at 25 °C and shrimps were fed every two days on commercial ORGANIX granulate shrimp pellets. A constant light:dark cycle was enforced (lighting hours 07:00-19:00).