Showing papers in "Fish Physiology in 2016"

The Concept of Stress in Fish

Abstract: 1. Introduction 1.1. What Is Stress? 1.2. Dynamics of the Stress Response and Effects on Performance 1.3. Contemporary View of the GAS: Eustress versus Distress 1.4. Sensory Systems and Perception 1.5. Adaptation versus Nonadaptation Aspects of the Stress Response 1.6. Key Unknowns The general physiological response of fish to threatening situations, as with all vertebrates, is referred to as stress. A stress response is initiated almost immediately following the perception of a stressor. Mildly stressful situations can have beneficial or positive effects (eustress), while higher severities induce adaptive responses but also can have maladaptive or negative consequences (distress). The stress response is initiated and controlled by two hormonal systems, those leading to the production of corticosteroids (mainly cortisol) and catecholamines (such as adrenaline and noradrenaline and their precursor dopamine). Together these regulate the secondary stress response factors that alter the distribution of necessary resources such as energy sources and oxygen to vital areas of the body, as well as compromise hydromineral imbalance and the immune system. If fish can resist death due to a stressor, they recover to a similar or somewhat similar homeostatic norm. Long-term consequences of repeated or prolonged exposures to stress are maladaptive by negatively affecting other necessary life functions (growth, development, disease resistance, behavior, and reproduction), in large part because of the energetic cost associated with mounting the stress response (allostatic load). There is considerable variation in how fish respond to a stressor because of genetic differences among different taxa and also within stocks and species. Variations within the stress response are introduced by the environmental history of the fish, present ambient environmental conditions, and the fish's present physiological condition. Currently, fish physiology has progressed to the point where we can easily recognize when fish are stressed, but we cannot always recognize when fish are unstressed because the lack of clinical signs of stress does not always correspond to fish being unstressed. In other words, we need to be aware of the possibility of false negatives regarding clinical signs of stress. In addition, we cannot use clinical data to precisely or accurately infer severity of a stressor.

Stress Indicators in Fish

Abstract: 1. Why Do We Measure Stress? 2. Quantifying Stress 3. Specific Measures of Fish Stress 3.1. Cellular and Molecular Indicators 3.2. Primary and Secondary Physiological Indicators 3.3. Whole-Organism Indicators 4. Considerations for Measuring and Interpreting Stress 4.1. Interspecific Differences 4.2. Intraspecific Differences 4.3. Context-Specific Differences 4.4. Stressor Severity 4.5. Field Versus Laboratory 4.6. Temporal Aspects 5. From Individual Indicators to Ecosystem Health 6. Stress Indicators of the Future 7. Conclusion A fish is chased with a net in an aquarium before being captured, scooped out of the water, and placed in a nearby testing arena. Is it stressed? How can we tell? Are our indicators reliable? Quantification of stress in fish has evolved from the initial development of radioimmunoassays to measure cortisol in plasma to the rapidly expanding suite of genome-based assays. Indicators range from the intracellular to whole-animal level. Expression of heat shock proteins (HSPs) and activity of metabolic enzymes can be paired with straightforward observations of reflexes and survival. Both traditional and emerging indicators have advantages and disadvantages, and their use is tissue- and context-specific. Ecological, biological, and methodological factors must be considered when selecting, measuring, and interpreting stress indicators. Inter- and intraspecific, sex, life stage, and temporal differences in physiological responses to stressors can confound confirmation of a stressed state. Despite numerous types of indicators, our understanding of how absolute levels of indicators relate to stressor severity and recovery to date remains limited. How accurately indicators characterize stress in wild populations naturally exposed to stressors is still an evolving discussion. The integration of research disciplines and involvement of stakeholders and user groups will aid in filling these knowledge gaps, as well as the translation of individual-level indicators to population- and ecosystem-level processes.

Stress and Growth

Abstract: 1. Introduction 2. A Conceptual Framework for Growth 2.1. The Dynamic Energy Budget (DEB) Model for Growth 2.2. Myocyte Growth 3. Stress Effect on Energy Available for Growth 3.1. Food Intake 3.2. Energy Substrate Absorption at the Gut 3.3. Energy Demand for Maintenance 4. Stress Effects on Promoters of Muscle Formation 4.1. Stress Effects on Myogenesis 4.2. Stress Regulation of the GH–IGF Axis 5. Conclusion and Knowledge Gaps In fish, muscle contributes over half the body mass and thus changes in the size of this organ system is considered to be of primary importance to growth. Muscle growth is the final consequence of a complex set of processes starting with the absorption of nutrients from the environment to their allocation for increases in myocyte number and size. Stress affects these processes, including energy utilization, absorption, and allocation, resulting in reduced muscle growth. Situations encountered in the wild such as predator avoidance or deteriorated water quality, or in captive situations such as handling, crowding, sorting, and grading may be stressful to the animal, entailing reallocation of energy away from growth to cope with stress. Here we highlight the potential role of cortisol, the principal glucocorticoid in teleosts, in regulating processes leading to muscle growth suppression. Stress-mediated elevation in plasma cortisol level affects energy intake, absorption, and utilization, including protein turnover and modulation of protective proteins expression, all leading to a decrease in energy available for muscle growth. Cortisol also modulates muscle growth regulators, including growth factors and transcription factors, causing growth suppression. Overall, there is a paucity of information on the mechanisms leading to stress effects on growth, but the available literature suggests a key role for stressor-mediated elevation in circulating cortisol levels and modulating muscle protein accretion in fish.

3 - The Endocrinology of the Stress Response in Fish: An Adaptation-Physiological View

Abstract: 1. Introduction 1.1. The Fish Forebrain 1.2. Stress 2. Stress and the Brain: The (Neuro-)Endocrine Hypothalamus 2.1. Fundamental Axes Interact 2.2. The CRF System 2.3. Ontogeny of the CRF System 2.4. Control Over the Pituitary Gland 2.5. CRF and Behavior 3. Stress and the Pituitary Gland 3.1. Adrenocorticotropic Hormone (ACTH) 3.2. Alpha-MSH 4. Stress and the Head Kidney 4.1. Catecholamine-Producing Cells 4.2. Steroid-Producing Cells 4.3. Communication Within the Head Kidney 4.4. Stress and Energy 5. Synthesis and Perspective For any organism dealing with environmental challenges, proper handling of stressful conditions is key to survival. Extant fishes represent the earliest vertebrates on earth and must have been masters in doing so, given their vast and sometimes fast radiation. Ancestral genome expansions (two or three whole genome duplication rounds) and stable water conditions contributed to their great ability to evolve and the eventual rise of tetrapods. An elaborate endocrine machinery provides the chemical mediation of a hypothalamically integrated signal to properly spend energy and allow for fight or flight when confronted with stressful conditions. We discuss developments in fish forebrain and (nonexhaustively) hypothalamic lay-out from the newest insights, obtained mostly from zebrafish studies. Corticotropin releasing factor, adrenocorticotropic hormone (ACTH), α-melanocyte-stimulating hormone, adrenaline, and cortisol, the key chemical mediators in the hypothalamic–pituitary–interrenal (HPI) axis, are passed in review and in the context of allostatic regulation of stress responses. We dedicate this chapter to Sjoerd E. Wendelaar Bonga, friend and teacher, who introduced us to the concept of stress and taught us to deal with it.

Stress and Disease Resistance: Immune System and Immunoendocrine Interactions

Abstract: 1. Introduction 2. Effects of Stressors on the Immune Response 2.1. Suppressive Versus Enhancing Effects 2.2. Perception of Stress After Immune Stimulation: Systemic Versus Local Responses 2.3. Stress and the Cellular and Humoral Immune Response 3. Organization of the Immune Response Following Stress: The Neuroimmunoendocrine Connection and the Role of the Head Kidney 4. Effects of Hormones on the Immune System 4.1. Hypothalamic Hormones 4.2. Pituitary Hormones 4.3. Interrenal Hormones 4.4. Receptor-Mediating Action of Cortisol in Fish Immunity During Stress Response 4.5. Somatotropic Axis and Fish Immune System 5. Environmental Stressors and Fish Immunity 5.1. Environmental Salinity 5.2. Temperature and Seasonality 6. Future Directions The endocrine-immune relationship of fish, particularly related to the stress response, is mediated by the close interaction of hormones and cytokines. In essence, stress can depress certain elements of the immune system and render fish vulnerable to infection and disease. This chapter summarizes the effects of stressors on disease resistance and the immune system and updates the knowledge on endocrine regulation of the immune system in fish, the effects at systemic and local levels, and the organization of the immune responses under stressed conditions, with special emphasis on the roles of hormones, their receptors, and system interactions. Basically, low levels of severity of stress (eustress) may lead to enhanced immune competence while greater severities tend to be immunosuppressive. The immune response to stressors are mediated by the endocrine system at both central and peripheral levels.

The Molecular Stress Response

Abstract: 1. Introduction 2. Molecular Regulation of the Hypothalamic–Pituitary–Interrenal (HPI) Axis 2.1. Hypothalamus 2.2. Pituitary 2.3. Head Kidney (Interrenal Tissue) 3. Genomic Cortisol Signaling 3.1. Glucocorticoid Receptor 3.2. Mineralocorticoid Receptor 4. Genomic Effects of Cortisol 4.1. Development of the Stress Axis 4.2. Molecular Adjustments During Stress 4.3. Cellular Adjustments 5. Significance of Molecular Responses 6. Approaches to Study Molecular Responses to Stress 6.1. Mechanistic Studies Using Targeted Mutagenesis 6.2. Epigenetic Regulation of Stress Response 7. Concluding Remarks and the Unknowns In this chapter we summarize the key patterns observed in the transcript abundances of genes involved in the hypothalamic–pituitary–interrenal (HPI) axis regulation, as well as regulation of stress-responsive genes that are modulated by corticosteroid signaling in fish. Plasma levels of cortisol, the primary corticosteroid in teleosts, rise within minutes after a stressor encounter, and this steroid action is mediated primarily by genomic signaling involving the family of nuclear receptors including the glucocorticoid receptor (GR) and mineralocorticoid receptor (MR). Specific molecular responses in target tissues associated with activation of these corticosteroid receptors have become apparent by increased use of receptor antagonists and gene knockdown tools. Although molecular adjustments to stress are dependent on species, developmental stage, type, and duration of stressor, overall cortisol action limits energy-demanding processes and enhances energy mobilization and reallocation. Recent work has also underscored the necessity of maternal cortisol and GR signaling as essential for fish development, but the underlying mechanisms are far from clear. While transcript abundance is an excellent indicator of pathway modulation by cortisol, this data by itself lacks physiological relevance unless accompanied by downstream protein and/or metabolite changes. As the field of molecular biology continues to advance, approaches including next-generation sequencing and gene editing tools will allow production of transgenic animals, even in nonmodel fish species, to reveal molecular mechanisms essential for stress adaptation. This fundamental knowledge may have relevance to improving the welfare of the organism in aquaculture and for protecting ecosystem health and biodiversity.

Stress Management and Welfare

Abstract: 1. Introduction 1.1. Defining Welfare 2. Managing Stress in Fish 2.1. Considerations for Care of Wild Fish in Captivity 2.2. The Impact of Psychological Stress 2.3. Controlling and Preparing for Stress 3. The Impact of Stress on Fish Welfare 3.1. Stress in Fisheries 3.2. Stress in Aquaculture 3.3. Stress in Recreational Fishing 3.4. Stress in Ornamental Fish 3.5. Stress in Research Within a Laboratory Context 3.6. Stress and Welfare in Wild Fish 3.7. Surgery and Anesthesia 4. Conclusions and Future Directions Stress poses a significant challenge to the health and welfare of fish in a variety of contexts. Preserving fish well-being has obvious benefits for aquaculture, fisheries management practices, large-scale fisheries, recreational fishing, research, and the ornamental fish industry. Healthy fish provide better economic return, contribute to population size, provide experimentally sound data, are attractive and pleasing to watch, and pose no risk to public health. However, many practices in each of these areas where fish are used cause stress and as such may impair fish welfare. The impact of routine procedures that fish are subject to is discussed to better understand how stress can be managed in captivity. The means of reducing stress and its deleterious effects on fish behavior, development, growth, reproduction, and immune function are considered as practical management tools that could be employed by those using fish if they wish to minimize stress and improve health. The opportunity to have a sense of control over stress or being able to anticipate and prepare for stress improves the ability of fish to cope with any stressors in their environment. Inescapable, unpredictable, or chronic stress leads to loss of control and allostatic overload. This can result in behavioral abnormalities leading to displaced aggression and stereotypical behavior. Thus, allowing fish to have other behavior options such as hiding or redirecting behavior can be provided by environmental enrichment. Conditioning fish to associate cues with the onset of a stress allows them to anticipate and prepare for stress, which can be beneficial. Operant conditioning, where fish can operate self-feeders, allows fish to control their own foraging behavior and also has positive effects on fish welfare. Providing the right kind of environmental and cognitive stimulation along with optimal environmental conditions, appropriate feeding regimes and social contact appear to be key to reducing stress in captive contexts if this is logistically possible. Practices in a variety of fish industries are considered where stress may be elevated with countermeasures suggested. Future studies should investigate implementing these factors to understand their impact in different circumstances and in different species if reducing stress is important. The development of robust stress indicators and automated alert systems based on behavior or environmental parameters to detect fish health will be vital for the assessment and alleviation of stress.

Variation in the Neuroendocrine Stress Response

Abstract: 1. Introduction 2. Ontogeny of the Teleost Stress Response 3. Neuronal Substrate for Stress and Variation in Stress Responses 4. Divergent Stress Coping Styles, Animal Personalities, and Behavioral Syndromes 4.1. Conserved Physiology of Contrasting Stress Coping Styles 4.2. Stress, Neuroplasticity, and Coping Style 4.3. Genetic Basis for Individuality 4.4. Stress Coping and Life History 5. Agonistic Interactions: Stress and Aggression 6. Nutritional Factors Affecting Stress Responses 6.1. Amino Acids 6.2. Fatty Acids 7. Directions for Future Research Between and within species, individuals vary in how and when they respond to stress and environmental perturbations. Neuroendocrine and physiological mechanisms mediating this flexibility are to a large degree conserved throughout the vertebrate subphylum, but are reviewed here with particular reference to adaptive variation in teleost fish. The influence of both genetic and environmental factors, such as the social environment and nutrient availability, can be exploited to reveal underlying proximate mechanisms. Associations between stress responsiveness, behavior, and life history traits likewise illuminate how natural selection apprehends and maintains individual variation.

6 - Homeostatic Responses to Osmotic Stress

Abstract: 1. Introduction 1.1. Osmoregulation in Fishes 1.2. pH Regulation in Freshwater and Seawater 1.3. Cell Volume Regulation 2. Responses to Hyperosmotic Stress 2.1. Monovalent Ions as Stressors 2.2. Divalent Ions as Stressors 2.3. Involvement of Hormones 3. Responses to Hypoosmotic Stress 3.1. Ionic Compositions as Stressors 3.2. Low pH as Stressors 3.3. Involvement of Hormones 4. Stress Sensing to Homeostasis 4.1. Osmosensors 4.2. Signal Transduction from Sensors 4.3. Targets of Intracellular Signaling Cascade 5. Energy Metabolism in Response to Osmotic Stress 5.1. Oxygen Consumption 5.2. Metabolism Modifications 5.3. Metabolites Transport 6. Conclusions and Perspectives The blood of fish is rarely similar to the water in which they reside, and thus they are constantly exposed to some level of osmotic stress. In addition, physiological stressors and associated responses may have profound hydromineral balance consequences (Schreck and Tort, 2016; Chapter 1 in this volume). The osmotic gradient between the fish and its environment is perceived by osmosensors and transduced through the intracellular signaling pathway to effectors in the osmoregulatory organs and initiates both general and osmospecific adaptive responses over different time scales ranging from the immediate posttranslational modification to the longer-term transcriptional regulation of genes. The former includes alterations in the activity of transport proteins and osmolyte-producing enzymes, cytoskeletal organization, vesicular trafficking, and metabolism. Recent studies using genomewide, molecular physiological approaches, together with emerging model species, help identify new transcription factors and effector molecules that play critical roles in adaptation to osmotic stress. In this chapter, we will review recent data on the osmotic stress response in fishes at different levels of biological organization (from gene to whole organism) and at different time scales (from acute to chronic response) to highlight what is known and to suggest areas for further study.

The Stress and Stress Mitigation Effects of Exercise: Cardiovascular, Metabolic, and Skeletal Muscle Adjustments

Abstract: 1. Introduction 2. Physiological Demands of Swimming Exercise and the Stress Continuum 2.1. Introduction 2.2. Neuroendocrine Aspects of Stress and Exercise 2.3. Energy Metabolism During Stress and Exercise 2.4. Cardiovascular and Respiratory Adjustments to Stress and Exercise 2.5. Limits of Swimming Exercise and Stress 3. Physiological Adaptations to Swimming and Relevance to Stress 3.1. Introduction 3.2. Effects of Swim Training on the Cardiovascular System 3.3. Effects of Swim Training on Feeding and Energy Metabolism 3.4. Effects of Swim Training on Skeletal Muscle Growth 3.5. Effects of Swim Training on Stress: Behavior, Health, and Welfare 3.6. Summary, Future Perspectives, and Key Unknowns Fish use swimming as their mode of locomotion and many species swim constantly to engage in feeding, migratory, reproductive, and predator avoidance behaviors. The vastly diverse lifestyles among fish species in different aquatic environments (eg, pelagic, benthic, anadromous) are reflected by extremely different capacities for swimming activity. Swimming, by way of increased activity of skeletal muscle and the cardiorespiratory systems, demands an increased production of metabolic energy to maintain homeostasis during and after exercise. Irrespective of swimming activity, a consistent feature of a stress response is the stimulation of the cardiovascular system and oxygen transfer and uptake to tissues. Fish must prioritize oxygen delivery in response to elevated metabolic states during stress and/or physical exercise. The provision and use of energy are fundamental determinants of physiological performance and swimming exercise can be viewed as both a potential physiological stressor and a stress-reducing mechanism. Swimming is generally classified as either burst or sustained according to intensity and duration. Burst swimming can impose significant stress upon many physiological systems, causing disturbances in metabolic, acid–base, osmotic, and electrolyte balance. In contrast, sustained swimming for extended periods does not lead to significant changes in circulating cortisol and catecholamines and yet can induce positive physiological responses and improved resistance to subsequent stressors. Specifically, sustained swimming in active species increases growth, improves aerobic performance, reduces cortisol levels, promotes schooling, and reduces aggressive interactions. In this light, restrictions in the natural swimming behavior imposed by aquaculture or a research setting may deprive fish of the physiologically beneficial effects of swimming and, consequently, may be stressful to fish. In this chapter we approach the topic of swimming as a potential stressor as well as a stress-reducing behavior that contributes to homeostasis and diverse phenotypic adaptations.

Reproduction and Development

Abstract: 1. Introduction 2. Regulation of Reproduction 2.1. Patterns and Environmental Regulation of Reproduction 2.2. Endocrine Control of Reproduction 3. Effects of Stress on Reproduction 3.1. Effects on Reproductive Performance 3.2. Effects of Stress on the Reproductive Endocrine System 3.3. Thermal Stress: A Special Case? 3.4. Effects of Hypoxia 3.5. Stimulatory Effects of Stress on Reproduction 4. Mechanisms of Stress Action 4.1. The Role of Cortisol: In Vivo Protocols 4.2. The Role of Cortisol: In Vitro Protocols 4.3. Effects of Other Stress Factors 5. Stress Effects on Reproduction in Natural Environments 6. Future Directions Stress has a consistent inhibitory effect on reproductive performance in fish of both sexes, but in a smaller subset of conditions can have stimulatory effects. Inhibitory effects include the suppression of ovarian and testicular development, inhibition of ovulation and spawning, and the production of smaller eggs and larvae. Long-term effects on progeny remain largely undescribed. Endocrine effects include the suppression of hypothalamic, pituitary, and gonadal steroid hormones, with the effects on the production of gonadal androgens and estrogens generally being most profound. Understanding the mechanisms by which stress interferes with reproduction is complicated by the fact that stress-modulated hormones can have systemic effects as well as direct effects on the reproductive endocrine system, and experimental paradigms often don’t allow distinction between the two. With that caveat, there is evidence for inhibitory effects on reproduction from all levels in the stress endocrine axis but strongest evidence is available for the role of corticosteroids, noting that the dominance of the literature by studies on the effects of cortisol is partly a reflection of the relative ease of measurement of steroid hormones. Proposed mechanisms of action include systemic metabolic effects, genomic glucocorticoid receptor-mediated effects and direct action through nongenomic processes that may include substrate competition for steroid-converting enzymes and binding proteins. The majority of stress studies have involved laboratory assessment of captive or cultured fish populations and there is much less information on the effects of stress among free-living, wild fishes. It is clear that reproductive processes can be maintained over a wide range of corticosteroid concentrations, but there is also increasing evidence that social control of reproduction may be mediated by stress processes. There remains scope for improved understanding of stress-reproduction interactions at all levels of reproductive function.

9 - Cognition, Learning, and Behavior

Abstract: 1. How Stress Can Affect Behavior, and Vice Versa 2. Optimality, Preferences, and Decision-Making 3. Salmon as Model Species 4. Learning in Relation to Stress in Fishes 4.1. Learning, Plasticity, and Problem Solving 5. Some Critical Knowledge Gaps We review the correlations, the connections, and the cause–effect relationships between behavior and stress in fish species. We relate the physiological aspects of stress to studies of fish behavior built on a foundation of observational and experimental studies that have stressed ecological and evolutionary considerations. Theoretical models of fish behavior, including contributions from experimental and comparative psychology, help us to understand the ways in which physiology can influence or direct behavior, and conversely the physiological consequences of behavior. Productive areas of current research bringing together studies of physiology, stress, and behavior include subjects as diverse as foraging and feeding behavior, migration, learning, parental and social behavior, and life history patterns. Broader studies of additional model fish species provide dramatic increases in our understanding of both mechanisms at the level of molecular genetics and consequences at the level of evolutionary ecology. We consider the central role of the concept of optimality and how it links the physiological and behavioral aspects of stress. Optimality in terms of physiology is considered in terms of proximate cause-and-effect relationships. For behavior, considerations of optimality more often refer to ultimate, evolutionary consequences. We show how optimality can bring together proximate and ultimate considerations of stress. We propose possible future research directions that will continue to enhance our understanding of both proximate and ultimate aspects of behavior and stress in fishes.

13 – Stress in Fish as Model Organisms

Abstract: 1. Introduction 2. Indicators of Stress in Laboratory Fish 3. Factors Impacting Stress in Laboratory Fish Handling 4. Housing 4.1. Density 4.2. Enrichment 4.3. Light/Dark Cycle 5. Feeding and Stress 6. Sex and Hierarchies 7. Sex Determination and Reversal 8. Stress, Cortisol, and Reproduction 9. Anesthetics 10. Underlying Diseases 11. Consistency 12. Conclusion and Key Unknowns With the advent of the zebrafish, the three-spined stickleback, and the medaka as laboratory animals, the emergence of fish as model organisms has provided a wide variety of potential experimental subjects, simultaneously introducing new challenges to both researchers and aquaculturists. With regard to stress in these fishes, we must shift the emphasis beyond the traditional definitions of production in terms of fecundity and growth and toward the goals of experimental consistency, animal welfare, and model robustness. In order to improve fish as model organisms, aquaculturists and researchers must use each organism's natural history as a template for developing appropriate husbandry practices. In this chapter, we review published data regarding stress in laboratory fishes in order to provide a foundation for building better husbandry protocols for the purposes of improving fish as model organisms.