Chapter 9 - Characterization of the neuroendocrine stress status as part of the multiparametric assessment of welfare in fish

Abstract

The welfare state of a fish strongly affects its physiology and behavior. Poor welfare conditions result in reduced growth rates and in a higher susceptibility to infections and disease and therefore, fish welfare is critical for a sustainable fish farming industry. Furthermore, recent scientific research has set evidence about fish sentience and cognition abilities that have been the base of the still increasing public awareness about fish well-being, which in turn has resulted in the development of stricter regulations when working with fish. In spite of its importance, quantifying fish welfare is not an easy task. It is currently considered that a precise evaluation of fish welfare requires a multiparametric approach based on the determination of both environmental and fish-based variables, the latter including an array of anatomical, physiological, and behavioral observations. Stress hormones and metabolites are among the most relevant physiological welfare-related variables, due to the close relationship between stress and welfare: stressful conditions or events are one of the most important determinants of poor welfare, particularly when the stressors are severe and/or sustained. Therefore determining the stress status of a fish constitutes an important part of its welfare assessment. However, the evaluation of the stress state might be also challenging, since fish, as other vertebrates, respond to stress by initiating a rather complex neuroendocrine response. This response comprises the activation of stress brain centers and the subsequent hormonal cascade leading to the release of stress hormones from the anterior kidney into circulation. In this chapter, the relevance and the methodology for quantification of different hormones and metabolites of the neuroendocrine stress response in fish, and their potential use in fish welfare assessment, is explained and discussed.