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
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 blood stream 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.
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.
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.
problems aren’t also the main issues for stress in fish. A study conducted by
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.
it comes to observing fish stress it can be difficulty. According to Ellis (as
cited by Y. Simon et al 2012), at present, a common method to identify stressed
fish is to analyze their blood cortisol levels, however this involves taking
the 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 fish
stress without having to remove the fish from the water.
clear indication of fish stress is a change in behavior. Some symptoms for
stress in fish include gasping at the surface, in which poor water conditions
results in a lack of oxygen. Others include poor appetite in which if the fish
is stressed, it will not eat or rapid gill movement or hiding away from other
fishes. While it is impossible to eliminate every stress, fortunately we can
prevent and treat some of them. Providing high quality nutrition and monitoring
and maintaining high water quality with the use of good sanitation practices ensures
fish are able to live in best conditions as possible. If a fish needs to be
transported elsewhere, although capturing immediately causes fishes distress,
if proper capture methods are used, it can help minimize the injuries and
summarize, like humans fishes feel stressed and its effects can have underlying
effects in our environment. We must be able to identify the problems and be
able to respond to it effectively. Remedying the potential problems and
minimizing stress for a fish ensures it lives a long and healthy life.