Crowding could have a positive effect on the welfare of tilapia by reducing aggressive behavior, but it can also make fish chronically stressed and more fearful
Written by: cabi.org
To what extent crowding results in abnormal behaviours that can impact welfare and stress coping styles in farmed fish is unclear. A study published in Royal Society Open Science provides novel insights into the effects of aquaculture intensification on neophobia (fear of the ‘new’) and stress coping styles in Nile tilapia (Oreochromis niloticus) – one of the world’s oldest farmed and most invasive fish.
Researchers at Swansea University reared juvenile tilapia for six weeks at either high (50 g l−1) or low density (14 g l−1), assessed the extent of skin and eye darkening (two proxies of chronic stress), and exposed them to a novel object in an open test arena, with and without cover, to assess the effects of density on neophobia and stress coping styles.
Fish reared at high density were darker, more neophobic, less aggressive, less mobile and less likely to take risks than those reared at low density, and these effects were exacerbated when no cover was available. Thus, the reactive coping style shown by fish at high density was very different from the proactive coping style shown by fish at low density.
The researchers say that the results of their study could have implications for welfare and management. “For example, skin and eye darkening appear to be related to stress coping styles, and given the relative simplicity of measurement, these could be incorporated into operational metrics of fish welfare, applicable under aquaculture conditions. Our results could also have implications for invasion biology because conditions that promote neophobia and a reactive coping style are expected to decrease invasion success.”