Using thermal choices as indicators for fish welfare

Citation

Rey Planellas S, MacKenzie S & Huntingford F (2019) Using thermal choices as indicators for fish welfare. ISAE 2019, Bergen, 05.08.2019-09.08.2019.

Abstract
Wild fish, being ectotherms, regulate their internal temperature by voluntarily moving within natural temperature gradients. In this way they make thermal choices (varying with developmental stage and in accordance with biological rhythms) that promote effective functioning of various biological systems. For example, selecting appropriate water temperatures enhances digestive efficiency in sharks and gonadal maturation in seabass and salmon. One manifestation of thermal choice of particular relevance to welfare and welfare indicators is the case of behavioural fever, in which pathogenic infection causes a short-term increase in preference for higher water temperatures. Behavioural fever occurs in invertebrates and in ectothermic vertebrates, including fish. In functional terms, enhanced internal temperatures induced by behavioural fever cause targeted up-regulation of immune function in infected fish, and strikingly improved survival rates. Ensuring that cultured fish have access to a temperature gradient will enhance fish welfare through improved health; this has been demonstrated in Tilapia ponds. Behavioural fever also offers the possibility of using thermal choices as an early-warning indicator for disease states. Another context in which the thermal choices are potentially informative about welfare status is the case of emotional fever, a temporary increase in body temperature shown in response to a variety of stressors. Physiologically induced emotional fever is well documented in endotherms, where it serves the function of promoting effective responses to challenge. Behaviourally-induced emotional fever has recently been demonstrated in zebrafish, stressed fish in a temperature gradient showing a transient increase in preference for warmer water following exposure to an acute stressor. Although this finding remains controversial, it potentially offers a sensitive behavioural indicator of stress and impaired welfare. In this talk we will illustrate the various beneficial effects of thermal choice in fishes and discuss their potential use as welfare indicators.

Keywords
welfare; thermal choice; fish; behaviour;