Stress is primarily a physical response when the body feels it is under attack The body enters a state of fight or flight and sets up the body for physical activity Similarly to humans fishes have the ability to cope with stress and its 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 requires a 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 by external conditions If severe enough fishes enter a distressed state that often leads to decreased performance which is a habitual undesirable aspect of production Most situations in which a fish experiences a change in its natural environment or a disturbance in its behavior are able to cause stress There are many different factors that influence stress in fish however stress protects the fish and ensures its survival As Bartelme 2010 states when a fish feels threatened the fish senses the threat and in response releases catecholamine and cortisol into the bloodstream which gives the fish an energy boost to help escape or evade the threat Catecholamines function as a hormone that helps the body respond to stress and prepare it for a fight or flight reaction while cortisol 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 few health effects while long term stress may lead to several illnesses some even contributing to death An example of long term stress include poor unsuited environment in which the fish cannot live in and tries to escape If escape is impossible the fish tries its best to slowly adapt to its new environment however this causes it stress weakening the effectiveness of its immune system Prolonging the stress may cause the fish to continue adapting for as long as necessary which ultimately causes it to fatally exhaust itself Additionally stress also plays a part for fish disease Naturally fish are often resistant to diseases however due to certain changes in its natural environment such as poor water quality inadequate nutrition or poor sanitation these changes reduce resistance by the fish The fish is more susceptible to disease and parasite infections which triggers its fight or flight response resulting in a burst of energy and increased blood pressure The energy and resources used by the fish for growth and increased resistance is now used for defense As Rottmann et al 1992 explains Fish are able to adapt to stress for a period of time they may look and act normal However energy reserves are eventually depleted and hormone imbalance occurs suppressing their immune system and increasing their susceptibility to infectious diseases
With a weak immune system the fish is more prone to spreading diseases and parasites Diseases that affect the fish may pose serious health risks or may lead to its death Environmental problems aren't also the main issues for stress in fish A study conducted by Goos and Consten 2002 found out that fishes react to stress with three different responses primary secondary and tertiary responses In the primary response the fish releases stress hormones cortisol and catecholamines into the bloodstream which trigger the physiological and behavioral mechanisms the secondary and tertiary stress responses Following the primary response the secondary response activates which releases more glucose into the blood for energy production and increases oxygen uptake and transfer Bartelme 2010 When a fish feels it is trapped and unable to escape the danger the tertiary response occurs These results in changes that include reduced growth rate decreased disease resistance change in behavior and reduced survivability When it comes to observing fish stress it can be difficulty
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