Data from: Density-dependent changes in neophobia and stress-coping styles in the world’s oldest farmed fish

Farmed fish are typically reared at densities much higher than those
observed in the wild, but to what extent crowding results in abnormal
behaviours that can impact welfare and stress coping styles is subject to
debate. Neophobia (i.e. fear of the ‘new’) is thought to be adaptive under
natural conditions by limiting risks, but it is potentially maladapted in
captivity, where there are no predators or novel foods. We reared juvenile
Nile tilapia (Oreochromis niloticus) for six weeks at either high (50g/L)
or low density (14g/L), 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. Our findings provide novel insights
into the plasticity of fish behaviour and the effects of aquaculture
intensification on one of the world’s oldest farmed and most invasive
fish, and highlight the importance of considering context. Crowding could
have a positive effect on the welfare of tilapia by reducing aggressive
behaviour, but it can also make fish chronically stressed and more
fearful, which could make them less invasive.