Tethering induces increased stress artifacts in social fish species

Behaviour of juvenile mulloway Argyrosomus japonicus were investigated under laboratory conditions to determine the efficacy of estimating predation mortality using tethering. The occurrence and duration of stressed behaviour was evaluated for individual A. japonicus that were hooked but untethered, hooked and tethered and unhooked and untethered (free swimming), both in schools and in isolation. Tethered and hooked treatments showed a significantly higher incidence and duration of stressed behaviour over controls, but stressed behaviour was lower for hooked but untethered fish in the presence of a school. Artifacts associated with elevated stress may reduce the reliability of estimates of relative predation derived from tethering data for schooling fishes.