Cortisol and finfish welfare

Abstract

Previous reviews of stress, and the stress hormone cortisol, in fish have focussed on physiology, due to interest in impacts on aquaculture production. Here, we discuss cortisol in relation to fish welfare. Cortisol is a readily measured component of the primary (neuroendocrine) stress response and is relevant to fish welfare as it affects physiological and brain functions and modifies behaviour. However, we argue that cortisol has little value if welfare is viewed purely from a functional (or behavioural) perspective-the cortisol response itself is a natural, adaptive response and is not predictive of coping as downstream impacts on function and behaviour are dose-, time- and context-dependent and not predictable. Nevertheless, we argue that welfare should be considered in terms of mental health and feelings, and that stress in relation to welfare should be viewed as psychological, rather than physiological. We contend that cortisol can be used (with caution) as a tractable indicator of how fish perceive (and feel about) their environment, psychological stress and feelings in fish. Cortisol responses are directly triggered by the brain and fish studies do indicate cortisol responses to psychological stressors, i.e., those with no direct physicochemical action. We discuss the practicalities of using cortisol to ask the fish themselves how they feel about husbandry practices and the culture environment. Single time point measurements of cortisol are of little value in assessing the stress level of fish as studies need to account for diurnal and seasonal variations, and environmental and genetic factors. Areas in need of greater clarity for the use of cortisol as an indicator of fish feelings are the separation of (physiological) stress from (psychological) distress, the separation of chronic stress from acclimation, and the interactions between feelings, cortisol, mood and behaviour.

Interplay between the endocrine and circadian systems in fishes

“…During the onset of stress, cortisol induces several catabolic processes that provide energy to the different physiological actions that occur to restore homeostasis (Mommsen et al 1999). A variety of biochemical, physiological and behavioural responses are also controlled by cortisol, such as energy metabolism, ionosmotic regulation, immunity and growth (reviewed in Mommsen et al 1999, Ellis et al 2012.…”

Sustained swimming mitigates stress in juvenile Brycon amazonicus reared in high stocking densities

“…Moreover, exercised fish in HD showed cortisol levels lower than those of fish in static water, which is compatible with the increase in liver glycogen. It should be pointed out that high levels of cortisol inhibit liver glycogen stores in fish (Ellis et al, 2012). Therefore, it is possible to presume that the increase of glycogen was a consequence of the cortisol effect, since its multiple physiological actions, including hyperglycemia, are reported to result in peripheral lipolysis and gluconeogenesis from proteolysis, as observed in cortisol implants in common carp (Cyprinus carpio) (Liew et al, 2013).…”

Effects of the Dietary Tryptophan and Aspartate on the Immune Response of Meagre (Argyrosomus regius) after Stress

“…Cortisol is the main glucocorticoid in fish and the hormone most directly associated with stress. Furthermore, at present it has also been correlated with fish welfare [5]. Indeed, stress levels are usually analyzed in relation to basal and post-stress cortisol levels, although some teleost species have a low cortisol response to stress, as in the case of meagre (A. regius, Asso 1801) [6].…”