Utilising spatial distribution in two-tank systems to investigate the level of aversiveness to crowding in farmed rainbow trout Oncorhynchus mykiss

High oxygen consumption rates and scale loss indicate elevated aggressive behaviour at low rearing density, while elevated brain serotonergic activity suggests chronic stress at high rearing densities in farmed rainbow trout

“…Indeed, low levels of cortisol and elevated brain stem 5-HTergic activity levels have previously 425 been associated with chronic stress in fish held at higher densities [6]. As a result, the 426 neuroendocrine indicators in the present study showed that stress levels were most elevated at the 427 highest density stocked, followed by the intermediate density and lowest at the low density.…”

“…Furthermore, in the study by Laursen et al [6], elevated serotonergic activity levels were found in 94 individuals held in crowded conditions.…”

“…The present study is unique in this regard, as the densities 58 examined here were reflective of levels of crowding established in a study by Laursen et al [6]. In 59 the aforementioned study, the spatial distribution of fish held at different densities in two-tank 60 systems was used to determine a level of aversion to crowding [6]. The aim of the present study was 61 to determine if being held at the chosen densities had an influence on indicators of welfare.…”

“…It may be speculated that previous research and the densities observed in 57 practice influenced these decisions. The present study is unique in this regard, as the densities 58 examined here were reflective of levels of crowding established in a study by Laursen et al [6]. In 59 the aforementioned study, the spatial distribution of fish held at different densities in two-tank 60 systems was used to determine a level of aversion to crowding [6].…”

“…In summary, here three densities were selected based on levels of crowding 96 determined using the spatial distribution of fish using two-tank systems [6]; an un-crowded low …”