The function of cortisol
Cortisol is a steroid stress hormone found in the bloodstream (Enzo Life Sciences, 2013). It is made from cholesterol (Enzo Life Sciences, 2013). This hormone not only is involved with stress responses but with metabolic and immunologic responses (Enzo Life Sciences, 2013). Activated by the HPA axis when facing a stressor, cortisol helps the body in a fight or flight situation (Ginis et al., 2011). The hormone is emitted in response to stressors like predators, social conflicts and confinement in an area (Gabor & Contreras, 2012).
Effects of continued cortisol release
Severe chronic stress is identified as prolonged periods of high cortisol concentrations ...view middle of the document...
, 2011); meaning, more stress an organism has, the less it will be able to forage for food. Social interaction with other fish and a fish’ social status is an acute stressor (LeBlanc, Middleton, Gilmour, & Currie, 2011). The following lists chemical stressors that are specific to fish: poor water quality due to low dissolved oxygen or improper pH, pollution, and nitrogenous and other metabolic wastes (Francis-Floyd, 2012). Some of the biological stressors include population density, other species of fish, and microorganisms (Francis-Floyd, 2012). Physical stressors that could affect fish are temperature, light, sounds, and dissolved gases (Francis-Floyd, 2012). Stress can affect learning and cognition (Clark, Boczek, & Ekker, 2011). The stressor temperature, especially cold temperatures can sometimes stop the immune system from working (Rottman, Francis-Floyd, & Durborow, 1992). Extremely high temperatures give way for pollutants and pathogens to thrive, decreasing the fish' ability to fight off infection (Rottman et al., 1992). High temperature also decreases the water's capacity to hold oxygen; because of this, the oxygen demand for fish increases (Rottman, et al., 1992).
Reproduction is fundamental characteristic of life. Fish, like most animals, reproduce and pass down their traits. Schreck stated that a small amount of stress is said to enhance reproductive abilities (as cited in Gabor & Contreras, 2012). However, both Milla and Schreck concluded that repetitive and severe stressors can have a detrimental effect on reproductive abilities (as cited in Gabor & Contreras, 2012). Because stress negatively impacts the foraging behavior, fish then have reduced growth rates; this in turn affects a fish's reproductive abilities (O’Connor et al., 2011). An environmental change that causes a significant amount of stress in a group of fish can affect even the population level (Pankhurst, n.d.).
Alternative blood sampling methods
In order to produce the best samples of blood, the method of extracting the blood must be efficient as possible. There are several ways to draw blood from fish and scientists have discovered non-invasive procedures. Fish experience stress when handled by humans, so methods have been developed to minimize this stress. Non-invasive sampling procedures have be found for sampling cortisol (Möstl & Palme, 2002). Hormone samples can be collected from the water due to the fact that hormones diffuse from the gills of the subjects into the surrounding water (Archard et al., 2012). Water-borne hormone collection methods are less stressful for the subject (Gabor & Contreras, 2012). Another method involves taking blood from an abdominal incision with a syringe (Hosoyo et al., 2008). Cortisol determination can be found in the urine, saliva, or fecal matter of the organism (Möstl & Palme, 2002). These methods are easily attainable without stressing the animal.
Other studies that...