Stressis primarily a physical response when the body feels it is under attack.
Thebody enters a state of ‘fight or flight’ and sets up the body for physicalactivity. Similarly to humans, fishes have the ability to cope with stress andits implications and as such get stressed the same way as humans do. As Bartelme(2010) puts it, stressor in fish could be defined as “a stimulus that requiresa physiological response by the animal in an attempt to adapt to that stimulus.In other words, stress is an internal physiological state that is caused byexternal conditions.” If severe enough, fishes enter a distressed state thatoften leads to decreased performance which is a habitual, undesirable aspect ofproduction.Mostsituations in which a fish experiences a change in its natural environment or adisturbance in its behavior are able to cause stress. There are many differentfactors that influence stress in fish; however stress protects the fish andensures its survival.
As Bartelme (2010) states, when a fish feels threatened,the fish senses the threat and in response releases catecholamine and cortisolinto the blood stream which gives the fish an energy boost to help escape orevade the threat. Catecholamines function as a hormone that helps the bodyrespond to stress and prepare it for a ‘fight or flight’ reaction whilecortisol is a hormone that helps regulate stress in the body.Moreover,fish stress can either be short or long term. Short term stress may lead to fewhealth effects while long term stress may lead to several illnesses, some even contributingto death. An example of long term stress include poor, unsuited environment inwhich the fish cannot live in and tries to escape. If escape is impossible, thefish tries its best to slowly adapt to its new environment however this causes itstress, weakening the effectiveness of its immune system. Prolonging the stressmay cause the fish to continue adapting for as long as necessary which ultimatelycauses it to fatally exhaust itself.
Additionally,stress also plays a part for fish disease. Naturally, fish are often resistantto diseases however due to certain changes in its natural environment such aspoor water quality, inadequate nutrition or poor sanitation; these changesreduce resistance by the fish. The fish is more susceptible to disease andparasite infections, which triggers its fight or flight response – resulting ina burst of energy and increased blood pressure. The energy and resources used bythe fish for growth and increased resistance is now used for defense. AsRottmann et al (1992) explains, “Fish are able to adapt to stress for a periodof time; they may look and act normal. However, energy reserves are eventuallydepleted and hormone imbalance occurs, suppressing their immune system and increasingtheir susceptibility to infectious diseases.
” With a weak immune system, thefish is more prone to spreading diseases and parasites. Diseases that affectthe fish may pose serious health risks or may lead to its death. Environmentalproblems aren’t also the main issues for stress in fish. A study conducted by Goosand Consten (2002) found out that fishes react to stress with three differentresponses: primary, secondary and tertiary responses. In the primary response,the fish releases stress hormones, cortisol and catecholamines into thebloodstream which trigger the physiological and behavioral mechanisms (thesecondary and tertiary stress responses) Following the primary response, thesecondary response activates, which releases more glucose into the blood forenergy production and increases oxygen uptake and transfer (Bartelme, 2010).When a fish feels it is trapped and unable to escape the danger, the tertiaryresponse occurs.
These results in changes that include reduced growth rate,decreased disease resistance, change in behavior and reduced survivability.Whenit comes to observing fish stress it can be difficulty. According to Ellis (ascited by Y. Simon et al 2012), at present, a common method to identify stressedfish is to analyze their blood cortisol levels, however this involves takingthe fish out from the water which is a stressful procedure for the fish .Y.Simon et al (2017) conducted a study that examines a behavior sensor for fishstress without having to remove the fish from the water.
Aclear indication of fish stress is a change in behavior. Some symptoms forstress in fish include gasping at the surface, in which poor water conditionsresults in a lack of oxygen. Others include poor appetite in which if the fishis stressed, it will not eat or rapid gill movement or hiding away from otherfishes. While it is impossible to eliminate every stress, fortunately we canprevent and treat some of them. Providing high quality nutrition and monitoringand maintaining high water quality with the use of good sanitation practices ensuresfish are able to live in best conditions as possible. If a fish needs to betransported elsewhere, although capturing immediately causes fishes distress,if proper capture methods are used, it can help minimize the injuries andstress.Tosummarize, like humans fishes feel stressed and its effects can have underlyingeffects in our environment. We must be able to identify the problems and beable to respond to it effectively.
Remedying the potential problems andminimizing stress for a fish ensures it lives a long and healthy life.