This document discusses stress in aquatic animals. It states that stress compromises the immune system and makes fish more susceptible to disease. Stress can be caused by poor water quality, overcrowding, handling, and other environmental factors. The document outlines the stress response in fish, including the release of hormones like cortisol, and how acute and chronic stress differ. It also discusses the immune system in fish and how stress can depress immune function. The key is for aquaculturists to minimize stressors and ensure optimal conditions for farmed fish.

1. Stress in
Aquatic Animals

2. Stress
Stress and disease are inter-
related, and control of these
factors is important for health of
fish and the success of any
aquaculture venture. Stress
causes physiological changes in
fish that compromise the immune
system which leaves the fish
species more susceptible to
disease. Stress comes a range of
environmental factors on the farm
The job of the aquaculturist is to
minimise stress on fish to ensure
they remain healthy.
Pathogen Factors:
•Bacteria
•Fungus
•Virus
•Parasites –
Protozoans, Metazoans
•Virulence strains
Environmental factors:
•Poor water quality
•Rough handling
•Incorrect stocking density
•Incorrect nutrition
•Aggressive interaction with other
fish
Host or Fish Factors:
•Mucous or slime
•Scales, skin etc
•Innate immunity like
white-blood cells
•Immunity and antibodies

3. Stress
The definition of stress is an abnormal physiological
condition in Finfish that results from an event. On
the fish farm, it occurs when the fish:
● Have been handled,
● Are in water quality outside their environmental
requirements,
● Are crowded together,
● Are affected by competition, inter or intra specific
aggression or pathogens,
● Are transported,
● Are medicated.
Our job is to manage these activities to reduce
stress.

4. Stress
The extent and duration of the response depends on the type and/or level of
exposure to the stress. A stressed animal will not thrive, grow or reproduce and can
die. Stressed animals also do not display well for customers.
Thus stress should be avoided at all costs!!
Sometimes we can prepare fishes response to stress, ie:
● Do not feed before handling or transport
● Maintain water quality at optimal levels
● Add salts and various chemicals to the water

5. The Stress Response
Stress response is the series of biological adaptive responses that occur in Finfish as
a result of a stress. This can be divided into 3 phases:
1.Alarm - fish arms itself for reaction
2.Resistance - fight or flight reaction
3.Exhaustion – acidosis, cramp, muscles and bodily functions stop.
Each level has a higher and more complex set of physiological responses that can
cause various negative reactions in the fish. Fish must adapt to this stress.
The Primary stress response involves the release of several hormones that help arm
the fish for a response. The first group are the Catecholamines which are an
immediate reaction to the stress. These ensure fish is ready to cope with or evade
stress.

6. The Stress Response
The second group are Adrenalins and noradrenaline produced by the brain. These
increase cardiac output, breaks down muscle glycogen, decreases ability to
osmoregulate. The third phase are the Corticosteroids, and this is often called the
adaptive phase. These include Cortisol which is produced by inter-renal tissue or
kidney, these decrease osmoregulation capacity, breakdown of glycogen and
proteins for energy.
Other responses include:
● Release of glucose into blood for energy,
● Increased oxygen uptake and blood flow to muscles. This results in dilation of
blood vessels in gill filaments, increased stroke volume of heart.
● Prolonged muscular activity leads to anaerobic respiration and excessive lactic
acid build-up or acidosis.

7. Acute and Chronic Stress
Stress can be divided into 2 types:
● Acute = short term stress through netting, grading,
bathing and other short term handling procedures.
● Chronic = long term stress with crowding, poor water
quality, poor environment.
The response to acute stress is generally Fight or Flight,
this is short term in nature and the fish generally try to
‘escape’ from the stress – for example when using a net to
catch the fish and they quickly swim away to evade capture.
However, in captivity stress may be more long term due to
changing water quality, handling, transport, and crowding.
These are typical chronic stressors and are generally the
cause of stress related illness and poor performance.

8. Immune System
All animals have in-built defence mechanism against disease. There are a broad
range of mechanisms including:
● Innate - always present ie skin, mucus, white blood cells. These have a
general activity and are not specific to any particular disease
● Acquired - specific antibodies/response to particular antigens.
Acquired immunity comes from Antigens from disease causing organisms that
trigger the immune system to produces innate and acquired responses such as
antibodies specific to the particular antigen or disease. Once the immune system
has antibodies to a particular disease it will generally easily prevent re-infection of
disease by rapidly producing antibodies once it recognises the disease. This
immune response is the principal of vaccinations, which are used to introduce
antigens so the immune system can develop its response or antibody to the
antigen.

9. The Immune Response
Immune Depressant
● Temp major factor - sub-optimal
decreases response
● Presence of heavy metals and
toxins
● Some medications
● Some stress
Immune Stimulants
● Vaccine
○ Expensive, few available
● Immunostimulants
● Proper nutrition
○ Vitamin C, B boosting
○ Some fatty acids
A variety of factors effect the immune system in either a positive (stimulant) of
negative (depressant) way:

10. Stress
Stress can be caused by a range of factors including:
● Incorrect or rough handling of stock during culture or capture
● Poor water quality
● Loud noises, bright lights, or movement above tanks
● Natural morphological and physiological life changes (e.g.
spawning)
● Incorrect feeds or feeding regime leading to poor nutrition
● Hierarchy behaviour due to large size or range of species
The extent and duration of the stress response depends on the
type and/or level of exposure to the stress. A stressed fish will
not grow at an optimum rate and can succumb to disease and
die, thus affecting productivity.
Thus stress should be avoided at all costs!!

11. Handling, Capture and Stress
Studies show that the stress response is rapid, with
Cortisol, glucose and lactate levels rising rapidly when
fish are stressed through handling and capture. The
longer or more severe the stress, the higher the levels of
these chemicals, which not only affect fish health but can
also affect post harvest and flesh quality. Farmers need to
be aware of this and therefore should ensure that:
● Fish are captured quickly,
● Handle fish gently,
● Ensure water quality is sufficient at all times,
● Avoid overcrowding of fish,
● Minimise handling, fish pumps are ideal,
● Minimise water quality differences when transferring
fish to new impoundment.

12. Therefore they
need to be
treated with
care.
Remember that:
FINFISH ARE FRAGILE!

13. Heat Stress Proteins (HSP)
Heat Shock Proteins (HSP) are a recent discovery in cell membranes and are
thought to maintain cell integrity. They are produced to maintain cell integrity during
stress such as temperature rises, toxins, O2 deprivation. Their production is short
term, but research suggests that foods high in Fatty Acids assist production of HSP.
New extract TEX-OE also useful, survival during transport or handling has
significantly increase using this.
In order for these HSP to be produced, it is important that fish receive good nutrition
so they have the necessary building blocks to produce these in times of stress.