Figure 2.

The use of bio-sensors to assess the effects of spatio-temporal variations in temperature and dissolved oxygen on farmed fish in sea cages. (a) Optimal temperatures and adequate levels of dissolved oxygen allow fish to use the full volume of the sea cage. (b) However, during periods of high temperatures and/or low water flow, stratification of the water column can result in the development of layers that fall outside the preferred environmental range of farmed fish leading to increased crowding. (c) Under such conditions, the high densities and increased activity of fish (as individuals are competing for space) can also result in localized depletions of dissolved oxygen, which further limits the preferred space within the sea cage. (d) As the situation becomes more extreme, temperature preferences are trumped by an active avoidance of low levels of dissolved oxygen, which forces fish to reside in areas outside of their optimal range and consequently impacts the growth, health and welfare of these individuals. The conceptual figure is based on findings from [47–49].