An overview of stress physiology of fish transport: changes in water quality as a function of transport duration

The fish gill is a multipurpose organ that, in addition to providing for aquatic gas exchange, plays dominant roles in osmotic and ionic regulation, acid-base regulation, and excretion of nitrogenous wastes. Thus, despite the fact that all fish groups have functional kidneys, the gill epithelium is the site of many processes that are mediated by renal epithelia in terrestrial vertebrates. Indeed, many of the pathways that mediate these processes in mammalian renal epithelial are expressed in the gill, and many of the extrinsic and intrinsic modulators of these processes are also found in fish endocrine tissues and the gill itself. The basic patterns of gill physiology were outlined over a half century ago, but modern immunological and molecular techniques are bringing new insights into this complicated system. Nevertheless, substantial questions about the evolution of these mechanisms and control remain.

Teleost fishes represent a highly diverse group consisting of more than 20,000 species living across all aquatic environments. This group has significant economical, societal and environmental impacts, yet research efforts have concentrated primarily on salmonid and cyprinid species. This review examines carbohydrate/glucose metabolism and its regulation in these model species including the role of hormones and diet. Over the past decade, molecular tools have been used to address some of the downstream components of these processes and these are incorporated to better understand the roles played by carbohydrates and their regulatory paths. Glucose metabolism remains a contentious area as many fish species are traditionally considered glucose intolerant and, therefore, one might expect that the use and storage of glucose would be considered of minor importance. However, the actual picture is not so clear since the apparent intolerance of fish to carbohydrates is not evident in herbivorous and omnivorous species and even in carnivorous species, glucose is important for specific tissues and/or for specific activities. Thus, our aim is to up-date carbohydrate metabolism in fish, placing it to the context of these new experimental tools and its relationship to dietary intake. Finally, we suggest that new research directions ultimately will lead to a better understanding of these processes.

Elasmobranchs (sharks, rays, and skates) are currently facing substantial anthropogenic threats, which expose them to acute and chronic stressors that may exceed in severity and/or duration those typically imposed by natural events. To date, the number of directed studies on the response of elasmobranch fishes to acute and chronic stress are greatly exceeded by those related to teleosts. Of the limited number of studies conducted to date, most have centered on sharks; batoids are poorly represented. Like teleosts, sharks exhibit primary and secondary responses to stress that are manifested in their blood biochemistry. The former is characterized by immediate and profound increases in circulating catecholamines and corticosteroids, which are thought to mobilize energy reserves and maintain oxygen supply and osmotic balance. Mediated by these primary responses, the secondary effects of stress in elasmobranchs include hyperglycemia, acidemia resulting from metabolic and respiratory acidoses, and profound disturbances to ionic, osmotic, and fluid volume homeostasis. The nature and magnitude of these secondary effects are species-specific and may be tightly linked to metabolic scope and thermal physiology as well as the type and duration of the stressor. In fishes, acute and chronic stressors can incite a tertiary response, which involves physiological changes at the organismal level, thereby impacting growth rates, reproductive outputs or investments, and disease resistance. Virtually no studies to date have been conducted on the tertiary stress response in elasmobranchs. Given the diversity of elasmobranchs, additional studies that characterize the nature, magnitude, and consequences of physiological stress over a broad spectrum of stressors are essential for the development of conservation measures. Additional studies on the primary, secondary, and tertiary stress response in elasmobranchs are warranted, with particular emphasis on expanding the range of species and stressors examined. Future studies should move beyond simply studying the effects of known stressors and focus on the underlying physiological mechanisms. Such studies should include the coupling of stress indicators with quantifiable aspects of the stressor, which will allow researchers to test hypotheses on survivorship and, ultimately, derive models that effectively link physiology to mortality. Studies of this nature are essential for decision-making that will result in the effective management and conservation of these species. Copyright © 2011 Elsevier Inc. All rights reserved.