VACCINOLOGY AND IMMUNITY OF AQUATIC ANIMALS
Location: Aquatic Animal Health Research
Title: Stress in Public Displayed, Cultured, and Pet Fish
Submitted to: Proceedings of the Annual Meeting of the American Veterinary Medical Associ
Publication Type: Proceedings
Publication Acceptance Date: November 20, 2006
Publication Date: July 14, 2007
Citation: Pasnik, D.J., Evans, J.J., Klesius, P.H., Welker, T.L. 2007. Stress in Public Displayed, Cultured, and Pet Fish. Proceedings of the Annual Meeting of the American Veterinary Medical Association. 144th AVMA Annual Convention July 14-18, 2007 Washington, DC.
Interpretive Summary: Stress in fish seems to be a vague issue, but laypeople, scientists and veterinarians routinely point to stress as a major contributor to fish disease and death. In fact, it is commonly believed that fish are highly susceptible to stress. The objective of this presentation will be 1) to help veterinarians understand the stress responses of fish and their impact on fish health and 2) to discuss what veterinarians and fish health professionals can do to mitigate stress in fish and their owners. Topics will include: 1) Review of primary (cortisol), secondary (glucose), and tertiary stress responses (homeostasis disturbance) and their pros and cons, 2) Causes of stress responses in fish (water quality, nutrition, aggression, handling, disease etc.), 3) Clinical and diagnostic signs of stress in fish and related effects (behavior changes, mucus sloughing, fertility problems, immunosuppression, elevated blood cortisol and glucose, disease, mortality, etc.), 4) Methods of treatment or prevention of stress (analgesics/anesthetics, medications, eradication of the offending factor, etc.), and 5) Evaluate current perspectives on consciousness and pain and how they influence our understanding of stress and fish well-being and welfare. In order to wrap up the discussion, the final discussion will present real-life, specific examples of how stress can impact fish health in three different settings where veterinarians work with fish and what veterinarians can do about it: 1) Public Displayed: how water quality, habitat, and cohabitation play a significant role in the viability of an aquarium exhibit, 2) Aquaculture: how intensive culture and feeding regimes affect growth, health, and product in a fish farm, and 3) Client-Owned Pet Fish: how transport of ornamental fish from a grow-out pond or a reef, on a truck, plane and/or automobile, and into a pet store tank can affect the quality and health of potential fish pets.
Whether fish are housed in public or private aquaria or in aquaculture or research facilities, the health and well-being of fish are readily affected by stressors. Stress in fish involves disruption of physiology and homeostasis occurring in response to adverse external influences and is capable of adversely affecting the fish. Several stressors are routinely encountered in fish husbandry, including: handling, transport, crowding, aggression, pollution, poor or fluctuating water quality (e.g. suboptimal temperature, low dissolved oxygen, high unionized ammonia), poor plane of nutrition, and disease. If any of these stressors are present or increased, the fish may have initial behavioral changes and then primary, secondary, or tertiary stress responses. Initially, acute behavioral changes may occur within seconds to minutes of stressor exposure. Primary responses involve increased corticosteroid and catecholamine hormone release (e.g. cortisol, epinephrine, norepinephrine) and may begin within minutes to hours later. Secondary stress responses include changes in hematological, metabolic, and hydromineral parameters (e.g. blood glucose and lactate, liver and muscle glycogen, osmolality) and may also begin within minutes to hours later. Tertiary responses involve changes in some whole-fish behavior and performance (e.g. homeostasis disturbances) and may begin minutes, hours, or days after stressor exposure. Fish must first perceive the stressor through sensations, such as discomfort, pain, or fright, which are detected by the central nervous system. The hypothalamic-pituitary-interrenal (HPI) axis is activated and increases cortisol secretion, thus mobilizing energy reserves and maintaining ionic balance in the face of a stressor. Following chromaffin tissue stimulation, epinephrine and norepinephrine are released. These responses may help the fish maintain homeostasis, but if stress responses are chronically activated through repeated or continuous exposure to a stressor, the effects may be detrimental. Such detrimental effects include decreased growth rates, immunosuppression, and increased disease susceptibility. Stress can have an effect on fish metabolism, presumably because energy utilized for stress responses is no longer available for other activities like growth. Further, initial behavioral changes like stressor avoidance may foster survival, but chronic stress and behavioral changes may lead to negative responses such as anorexia or lethargy. Stress can also hinder reproductive activities like gonadal steroid production, gamete quality, embryonic development, and larval survival. The immune system may also be suppressed, because stress-related hormones can reduce macrophage, lymphocyte, and antibody activity, thus leading to increased disease susceptibility.
One of the most important activities of fish health professionals is the prevention or management of stress in fish. Several methods to measure stress are available, including relatively easy methods such as test meters/kits for glucose and lactate or more complicated methods such as enzyme-linked immunosorbent assays (ELISA) or radioimmunoassays for cortisol measurement. Veterinarians will determine stress levels and their impact based on a combination of history, observation, and diagnostic tests. Important clinical and diagnostic signs of stress include behavior changes, poor body condition, mucus sloughing, reduced fertility, immunosuppression, and elevated blood cortisol and glucose. Two often-cited outcomes of stress-related problems are acute mortalities with no discernable cause and disease outbreaks accompanied by opportunistic organisms and delayed, chronic mortalities.
Stress can be prevented or mitigated through good husbandry practices, such as: ensuring proper water quality through water changes, tank cleanings, and biological and chemical filters; ensuring a good plane of nutrition according to the fish species involved; preventing overcrowding, adverse social interactions, and excessive handling; routinely disinfecting equipment and tanks using chemical disinfectants on the tanks and husbandry paraphernalia and using water sterilization equipment (e.g. UV light); and vaccinating fish for endemic diseases when possible. Symptomatic treatment may also be required, including the use of salt for osmoregulatory disturbances or medication against infections. Fish may also be helped by treatment with analgesics/anesthetics (e.g. tricaine methanesulfonate) if stressful procedures like handling, transport, or surgery are required. It should be noted that some treatment methods and/or medications can cause stress themselves, so the utilized medication should be chosen carefully based on the procedure, fish species, environment, and applicable laws. Several scientists have also examined alternative types of stress-mitigation including genetic and nutritional improvement. For example, since there are differences in the way individuals, strains, and species of fish respond to stressor exposure, considerable effort has been made to breed stress and disease-resistant fish. Certain evidence also suggests that dietary supplements can be used to increase stress resistance in some fish.
Stress responses are adaptive responses and their consequences are not necessarily detrimental. However, the effects can be negative, especially if the exposure is acute or prolonged at low levels. The consequences and magnitude of stress responses also depend on several other factors: genetic makeup, stage of development, pre-existing environmental conditions, and duration and type of stressor. Because stress is closely related to health and disease in fish, fish health professionals should familiarize themselves with fish stressors, stress responses, and treatment options. The following references were used for these AVMA convention notes, and together they provide deeper understanding of stress and its impact on fish health.