This document discusses stress in fish and its relationship to disease susceptibility. It defines stress and identifies various stressors fish face in both wild and captive environments. Chronic stress from factors like poor water quality, temperature fluctuations, overcrowding and nutritional deficiencies weakens the immune system and makes fish more prone to infection. The document examines the physiological response to stress and how it can ultimately lead to tertiary responses like reduced growth and disease resistance if stressors are not addressed. Controlling stressors is important for aquaculture health management and disease prevention.

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Introduction:
It has been long recognized that stress increases disease susceptibility. Therefore disease is
not just the presence of pathogens but results from a combination of factors. As a result we
have to be wary of concentrating solely on the role of pathogens in the etiology of infectious
diseases. Since the 1980s a great deal of work has been conducted on the relationship between
stress and disease susceptibility, which has resulted in a much improved understanding of
stress and disease. This includes the nature and evolutionary context of the immune and the
stress responses. Despite a more profound understanding of the internal systems we must still
be aware of the direct and indirect effects of stressors in order to understand and control
diseases in fish. Although individual variability and population level effects make it difficult
to predict the outcome in specific circumstances, general principles have important
implications for aquaculture health management.
Stress:
Stress is a critical factor in fish health. It is so important, in fact, that scientists have studied it
in detail, both in the wild and in captive fish. Stress is a very complicated subject that
permeates every aspect of fish-keeping.Stress is a condition in which an animal is unable to
maintain a normal physiological state because of factors adversely affecting its well-being.
Symptoms:
 Gasping at the Surface: fish is gasping his mouth at the surface, this is a sign of stress
brought on by poor water conditions, usually a lack of oxygen.
 Appetite: fish is stressed, oftentimes he will not eat.
 Disease: Ich, characterized by white spots on the body of a fish, and other diseases can
appear as a result of your stress. If you observe this or any other visible ailments or
sores on your fish, you should talk to your veterinarian about possible treatments.
 Strange Swimming: When fish are stressed, they often develop odd swimming
patterns. If your fish is swimming frantically without going anywhere, crashing at the
bottom of his tank, rubbing himself on gravel or rocks, or locking his fins at his side,
he may be experiencing significant stress. Talk to your veterinarian about treatment
and look into what may be causing the stress and alleviating it.

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Stressor:
A stressor is a chemical or biological agent, environmental condition, external stimulus or an
event that causes stress to an organism.It include overcrowding, handling, a poor or
unfavorable environment, inappropriate or aggressive fish sharing the same tank and, in the
wild, predators. All of these (and others) cause fish to react in different ways depending on the
type and amount of stress
Stress may be of following types :
1. Chemical stressors.
2. Biological stressors.
3. Physicalstressors.
4. Procedural stressors.
These are described in below :
1. Chemical stressors:
Chemical stresses also produce biomechanical responses associated with metabolism and
tissue repair.
Water quality: Reduce oxygen, improper pH etc.
Pollution:
1. Intentional: Chemical treatments.
2. Accidental: Insect spray,spills.
Diet composition: Protein,CHO.
Nitrogenous & other metabolic waste: Accumulation of ammonia or nitrite.
2. Biological stressors:
 Population density
 Other species of fish: Aggregation,territoriality,lateral swimming space.

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 Microorganism: Pathogenic,internal,external.
 Algal population
3. Physical stressors:
• Temperature
• Dissolve oxygen
• Light
• Sound.
4. Procedural stressor:
• Handling
• Stocking
• Disease treatment
• Feeding method.
The above stressors are categorised as either acute or chronic depending on their duration and
frequency. Fish stressors of both types have severe negative effects on the animal's growth and
health.
Acute : Acute fish stressors are events which the animal experiences for a short period of
time such as handling, transport, manipulation (sorting, vaccinations, partial fishing ...), and
sudden changes in water quality (water safety, oxygenation, composition).
Chronic : Chronic fish stressors are defined as a constant or recurring exposure that causes a
prolonged physiological response such as xenobiotic in water, overcrowded ponds, a non-
homogeneous population, uneven feed distribution, inadequate oxygenation
The Physiological Response to Stress in Fish and Shrimp:
Generally, stress in fish is a non-specific response classified as three distinct responses:
Primary response : The primary response is characterised by the activation and the
secretion of the hormones, corticosteroids (cortisol) and catecholamines, into the
blood.

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Secondary response : The release of hormones triggers the secondary response which
involves the release of glucose into the blood for energy production, followed by
increases in heart rate, gill blood flow and metabolic rate which causes changes to
blood lactate and hematocrit.
Tertiary response : Changes in blood physiology ultimately cascade into a whole
body change or the tertiary stress responses. Changes associated with the tertiary stress
response include reduced growth rate, decreased disease resistance, altered behavior
and reduced survivability.
Fig: Physical, chemical and other perceived stressors can affect fish and cause
primary, secondary, and/or whole-body responses. Adapted with permission from
Barton, 2002.

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Causes of stress in fish:
 Elevated ammonia
 Elevated nitrate
 Improper pH level
 Fluctuations in temperature
 Improper salinity
 Low oxygen levels
 Harassment from other fish
 Lack of hiding places
 Lack of enough fish to provide schooling
 Inadequate pond size
 Overstocking
 Medications and water treatments
 Improper nutrition
 Harvesting and shipping of fish
Elevated Ammonia and Nitrite : Elevated ammonia, nitrite, and nitrate all create
deterioration in fish health due to stress. High levels can cause severe stress, whereas slightly
elevated levels can contribute to chronic stress.

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Improper ph level: pH levels that change abruptly cause acute stress and continually
elevated or lowered pH levels can cause chronic stress. Many fish adapt to long-term
changes, but there are limits. pH changes of more than 1.5 points below or above
recommended levels are going to have a negative effect over time and should never be
considered acceptable.
Fluctuations in Temperature: Temperature fluctuations are a much underappreciated
stressor of fish. Most tropical freshwater and marine fish do not tolerate temperature changes
very well. The daily fluctuations will create chronic stress as will having too low or too high
of a temperature in the tank for the species of fish present.
Improper Salinity: Wild fish live within very specific salinity levels (levels of salt in the
water). Their bodies work hard to maintain the osmotic gradient between themselves and
their environment. If their environmental salinity is not specific to their needs and is not held
at a steady level, they have to work harder to maintain their osmotic gradient, which
generates chronic stress.
Low oxygen levels: Oxygen levels that are below recommended levels can cause fish to
'breathe' faster than optimum and this can result in chronic stress. Obviously, very low
oxygen levels can lead to severe short-term stress and death.
Harassment from other fish : Harassment from other fish and lack of hiding spaces go
hand in hand. There should be two suitable hiding spaces for every fish in the tank,
otherwise, there are going to be fish that are stressed and bullied. Remember that unlike their
environment in the wild, these fish are confined and cannot get away from aggressors.
Aggression is a very real problem in many tanks that leads to many injuries, infections, and
death.
Overstocking: Overstocking is a common problem that contributes to almost all of the
stresses in the above list, from water pollution to oxygen depletion to harassment.
Medications and Water Treatments: To treat a disease or water condition by adding
chemicals, one should be aware that it can be stressful to fish. Copper is an excellent
treatment for saltwater ich or marine velvet disease, but it can be toxic and stressful to fish

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Improper Nutrition: Improper nutrition is also a commonly overlooked stressor of fish.
Many fish can live on minimal nutrition with old or stale flake foods, but this poor nutrition
is a chronic stress.
Disturbing the Pond: Disturbing the pond through banging on the glass, constantly netting
fish, or rearranging décor stresses fish and should be kept to the necessary minimum.
Pollutants: Pollutants are foreign substances, generally chemical compounds, that enter the
fish systems from an outside source. Those contaminants can either kill fish directly or cause
physiological stresses in the fish. Some pesticides can remain in the tissues of apparently
healthy fish and under conditions of stress, due to another factor, may be released in to the
blood stream of the fish and compounding the susceptibility to disease or even resulting in
death.
Some of the stressors impacting the shrimp health:
1. Rapid changes in temperature
2. Rapid changes in pH
3. Salinity fluctuations
4. High suspended solid loads
5. Density (crowding)
6. Insufficient oxygen
7. Elevated CO2
8. Nitrites
9. Unionized ammonia
10. Heavy metals
11. Toxins (algal, bacterial, feed)
12. Pesticides
13. Nutrition (usually inadequate)
14. Molting
15. Handling
16. Parasitism
17. Low level infections
18. Disease
19. Hydrogen sulfide
20. Climatic conditions like continuous
rains

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Stress Parameters :
In order to become a tool, stress should be measurable. It is necessary to measure the stress
response in order to anticipate its consequences. The occurrence of stress will cause various
types of response:
 Hormonal: cortisol, catecholamines.
 Metabolic: increase in oxygen consumption, changes in the blood’s salt concentration;
 Behavioral: grouping of fish, increased swimming speed.
It is more or less easy to quantify these indicators. Once the extent of stress is assessed, its
effects can be categorized by analyzing the level of the response triggered:
Fig : The different levels of response to stress in fish and their impact on the
animal's condition

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 A first level of response relates to a light and short-term stress. These episodes of stress can
trigger the release of hormones that put the body in a state of high alert. If they don’t recur too
often, their impact on rearing performance are moderate to non-existent.
 A second level, resulting from a longer exposure to a more intense form of stress, will compel
the animal to mobilize its resources in order to cope with the ensuing metabolic demand. At
this level of exposure, stress has a definite impact on the productivity of the population in
question.
 The third level marks a prolonged exposure to a very high level of stress. This level
corresponds to the point beyond which the fish’s resources are no longer sufficient to
efficiently fight against the perturbation endured.
Relationship between stresses, infection, disease:
Host + pathogen+ environmental factors
Weak and stress (stage 1)
Infection (stage 2)
Disease (stage 3)
Stress Management :
The correct management of stress provides positive benefits through rapid return to feeding
and improved health performance.

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Fig : stress management

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Fish disease:
Fish disease is a substantial source of monetary loss to aquaculturists. Production costs are
increased by fish disease outbreaks because of the investment lost in dead fish, cost of
treatment, and decreased growth during convalescence. In nature we are less aware of fish
disease problems because sick animals are quickly removed from the population by predators.
In addition, fish are much less crowded in natural systems than in captivity. Parasites and
bacteria may be of minimal significance under natural conditions, but can cause substantial
problems when animals are crowded and stressed under culture conditions.
Types of fish disease:
There are two broad categories of disease that affect fish, infectious and non-infectious
diseases. Infectious diseases are caused by pathogenic organisms present in the environment
or carried by other fish. They are contagious diseases, and some type of treatment may be
necessary to control the disease outbreak. In contrast, non-infectious diseases are caused by
environmental problems, nutritional deficiencies, or genetic anomalies; they are not
contagious and usually cannot be cured by medications.
Infectious Disease :
Infectious diseases are broadly categorized as parasitic, bacterial, viral, or fungal diseases.
 Parasitic diseases of fish are most frequently caused by small microscopic organisms
called protozoa which live in the aquatic environment. medications. here are a variety
of protozoans which infest the gills and skin of fish causing irritation, weight loss, and
eventually death. Most protozoan infections are relatively easy to control using standard
fishery chemicals such as copper sulfate, formalin, or potassium permanganate.
 Bacterial diseases are often internal infections and require treatment with medicated feeds
containing antibiotics which are approved for use in fish by the Food and Drug
Administration. Typically fish infected with a bacterial disease will have hemorrhagic
spots or ulcers along the body wall and around the eyes and mouth. They may also have
an enlarged, fluid-filled abdomen, and protruding eyes. Bacterial diseases can also be

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external, resulting in erosion of skin and ulceration. Columnaris is an example of an
external bacterial infection which may be caused by rough handling.
 Viral diseases are impossible to distinguish from bacterial diseases without special
laboratory tests. They are difficult to diagnose and there are no specific medications
available to cure viral infections of fish.
 Fungal diseases are the fourth type of infectious disease. Fungal spores are common in
the aquatic environment, but do not usually cause disease in healthy fish. When fish are
infected with an external parasite, bacterial infection, or injured by handling, the fungi
can colonize damaged tissue on the exterior of the fish. These areas appear to have a
cottony growth or may appear as brown matted areas when the fish are removed from the
water. Formalin or potassium permanganate are effective against most fungal infections.
Non-infectious Disease:
Non-infectious diseases are broadly categorized as environmental, nutritional, or genetic. These
problems are often corrected by changing management practices.
Some Infectious Diseases of Fish:
 Ulcers
Caused by Pseudomonas and Aeromonas bacteria
Symptoms:
Pinky-white open wounds, often with a white edge and sometimes secondarily infected by
fungi and other bacteria.
Reason for Infection:
Very poor water quality or an excessively high pH level. Minor scratches can become infected
if conditions are poor.Also commonly affects newly imported Koi and goldfish.
Action:
Test the Water for signs of ammonia and nitrite. Conduct a large water change to reduce
pollution levels.

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Treatment:
Fish lose salts quickly through open wounds,so add aquarium salt at a dose of 1-3g/litre. Use
an anti ulcer treatment.If treatment fails, a vet can prescribe stronger antibiotics.
 Cloudy eye
Caused by poor water quality, poor diet, eye flukes, corneal damage, bacterial infection.
Symptoms:
Entire surface or lens of eye takes on a cloudy, opaque appearance. There may be a build-up
of mucus on the outer surface.
Reason for Infection:
Most commonly caused by poor water conditions. A lack of vitamins in the diet may also
cause clouding. On rare occasions digenetic flukes, such as Diplostomum, can cause problems.
Action:
Improve water conditions. Use a good quality food containing added vitamins.
Treatment:
Improving water conditions usually cures cloudy eyes. Eye flukes are uncommon and can be
difficult to accurately diagnose and treatment.
 Dropsy
Usually caused by bacterial infection. Viral infection, nutritional, metabolic and osmo-
regulatory problems can also be responsible
Symptoms:
Swelling of the body cavity due to a build- up of fluid. Scales become raised giving a pinecone-
like appearance. One or both of the eyes may be protruded.
Reason for Infection:

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Usually triggered by poor water quality, especially the presence of ammonia and nitrite. Often
confined to individual fish.
Action:
Test water and improve water conditions immediately. Aquarium salt at a dose of 1- 3g/litre
can help to prevent salt loss.
Treatment:
Can be difficult to
 White spot
Causedby Ichthyophthirius multifiliis parasite
Symptoms:
Small white spots, about the size of a salt grain, on the skin, fins and gills.
Reason for Infection:
Stress related. Usually a consequence of poor or incorrect water conditions, fluctuating
temperature and general poor husbandry. Sensitive species may develop white spot as a
result of being introduced to a new aquarium.
Action:
Ensure the water is free of pollution and isolate cause of stress.
Treatment:
Treat promptly with an anti- parasite medication. It may be necessary to raise the water
temperature to improve the effectiveness of the treatment. Wounds left by parasites may
become secondarily infected.
 Bacterial infection
Caused by Aeromonas and Pseudomonas bacteria
Symptoms:
Reddening of the skin or fins; ragged fins with signs of infection, open sores. Common on
many newly imported fishes. Often accompanied by other diseases, including fungi.

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Reason for Infection:
Poor water conditions, especially the presence of ammonia and nitrite. Wounds resulting from
poor handling, transport or fighting may become secondarily infected by these bacteria if
conditions re poor.
Action:
Improve water conditions, and treat promptly.
Treatment:
Use a proprietary treatment as soon as possible. Aquarium salt at a dose of 1- 3g/litre can
help prevent salt loss. Severe infections may require prescription medications from a vet.
 Fungus
Causedby Saprolegnia and Achlya
Symptoms:
Fluffy growths affecting wounds on the skin and fins of freshwater fishes.
Reaction for infection:
Usually a secondary infectionthat invades wounds left by ulcers and parasites, including
whitespot. Rarely a problem in tanks with
Action:
Improve water conditions andtreat promptly.
Treatment:
Standard anti- fungal medications, such as methylene blue, are usually very effective, but
may affect filtration and water quality.

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Some of The Infectious Diseases of Shrimp:
 Vibriosis
The term 'vibriosis' refers to infections of shrimp caused by species of bacteria within the genus Vibrio.
In general, Vibrio spp. are opportunist pathogens that occur commonly in the pond environment. Thcir
pathogenicity (ability to cause disease) varies between species and even betwecn strains within a species.
They are usually associated with disease in shrimp stressed for a wide range of reasons. Systemic vibriosis
is often jassociated with poor environmental conditions or is superimposed on another disease as the
shrimp's condition deteriorates.
Identifying clinical sign:
Acutely affected shrimp with systemic vibriosis can be lethargic and gathered at pond edges; in some
cases they will be red-coloured.
Treatment:
Treatment of vibriosis requires Improving the pond environment to reduce poor water quality conditions
and allow natural conditions to prevail.
 Black splint disease
It has been suggested that low salinities and specific bacteria such as Vibrio aiginoiyliclls that proliferate
in the lower salinities can cause black splint disease. It is likely that a specific set of pond conditions and
any proliferation of bacteria in the pond water can lead to black splint disease.
Identifying clinical signs:
Large black nodules in the centre of the tail muscles.
Prevention:
Manage the pond to avoid pond bottom fouling. Control feeding rates. Avoid sudden salinity changes.
 Red gills
From low dissolved oxygen or high toxin such as ammonia or hydrogen sulphide concentration.

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Identifying clinical sign:
Pink to red gills.
Prevention:
Maintain optimum pond environment.
 Black gills
Significant organic fouling in the pond bottom or algae die-off..Blue-green algae growing on gill
filaments. Infectious damage to the filaments and melanisation. Exposure to iron salts.
Identifying Clinical Signs:
Shrimp gills clogged with brown to black material, gives a dirty or muddy look. Melanisation of gills
produces blacking discolouration.
Prevention:
1. Check for acid sulphate soil in ponds.
2. If it is acid sulphate free, drain and clean out the pond bottom. Then liming.otherwise the
filamentous algae will tend to grow
3. Aerate the pond as for high stocking densities for a 1 hectare pond.
4. Liming the ponds.
 Tail cramping diseases
Assumed to be caused by effects of high temperatures and or salinities when combined with the stress of
handling (may not occur without handling).
Identifying clinical signs:
Shrimp tail is cramped up and will not relax, usually after handling, such as cast net sampling. Some may
show white muscle from stress.
Prevention:
Minimise handling or delay harvesting until the problem is solved.

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 Shirmp red diseases
It is caused by the V. paraheamolyticus, V.damseal, V. anguillarium bacteria. Also affected for using
excessive lime(4 ton/ha) and presence of more CO2(30-60 ppm).
Identifying clinical sign:
Red gill, grey hepatopancreas and weak body of shrimp.
Prevention:
1. Water of affected pond should changed for two times in a day.
2. Clean the bottom of the pond
3. Water quality management should be properly maintained.
 Yellow head diseases
Yellowhead disease (YHD) is a viral infection of shrimp and prawn. Increasing salinity and temperature
is responsible for this diseases
Clinical sign:
The cephalothorax of infected shrimp turns yellow after a period of unusually high feeding.
Prevention:
Ensure proper water quality and adequate phytoplankton.
 Hepatopancreatic Parvovirus (HPV) Disease
Typically affects mid-juvenile stages with signs of necrosis and atrophy of the hepatopancreas, poor
growth rates, anorexia and reduced preening with a concurrent increase in surface and gill fouling by
epicommensal organisms. Increased mortality, particularly under stress or crowding conditions has been
noted.
Prevention:
1. Frequently change the water
2. Separate the affected shrimp
3. Water quality should be maintained

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 Soft shell diseases
The loose shell syndrome is an economically significant disease of Paeneusmonodon culture. More Ph,
less changing rate of pond water, insecticide in water are responsible for this.
Clinical sign:
The affected shrimp has a paper-like carapace with a gap between the muscle tissue and carapaces. The
affected shrimp loses weight during culture and turns into a soft leathery shell.
Prevention:
1. Balance diet
2. Regularly check the water quality
 Muscle necrosis
The cause of muscle necrosis are due to low DO, sudden temperature and salinity change, overcrowding
and rough handling.
Clinical sign:
White opaque areas in striated muscle especially of the abdominal segment.when distal portion of the
abdomen become necrotic turns red and begin to decompose
Prevention:
keep parameters (DO, temperature, salinity, overcrowding, handling etc) in suitable range to minimize
stress.
Prevention of disease:
Numerous books and articles have been written on the diagnosis and treatment of specific fish diseases;
however, prevention through good management practices is the best control measure to minimize disease
problems and fish kills. Good management involves maintaining good water quality, preventing injury
and stress during handling providing good nutrition, and using sanitation procedures. The following are
management practices that help prevent stress and the resulting fish kills.

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Water quality
 Do not exceed carrying capacity of fish in ponds and tanks.
 Monitor water quality parameters.
 Maintain dissolved oxygen levels above 5 mg/L. Sub-optimum levels of dissolved oxygen, while
not immediately lethal, may stress fish, resulting in delayed mortality.
 Prevent the accumulation of organic debris, nitrogenous wastes (ammonia and nitrite), carbon
dioxide, and hydrogen sulphide.
 Maintain appropriate pH, alkalinity, and temperature for the species.
Handling and transporting
 Use capture methods that minimize physical injury and stress.
 When possible, use knitted mesh nets rather than knotted nets to reduce injury and scale loss.
 Speed and gentleness when handling fish are of utmost importance.
 Minimize the number of times the fish are lifted from the water, and work as quickly as possible
when transferring fish.
 Harvest, handle, and transport fish at times when fish are least susceptible to stress and infection.
 Transport and holding tanks should be large enough to allow complete freedom of movement of
fish and have no sharp corners or edges that might injure the fish.
 Maintain optimum water conditions while capturing, hauling, and handling fish.
Nutrition
 Feed a high quality diet that meets the nutritional requirements of the species.
 Use proper feeding rate (either over-feeding or starving the fish should be avoided).
 Store feed in a cool dry place to 4. Dispose of dead fish properly prevent deterioration. If avail- to
prevent spread of disease. able, a freezer is ideal for storing fish feed.
Sanitation
 Prevent disease-carrying fish from living in hatchery water supply (e.g., reservoir ponds, springs,
streams).
 Remove all dead fish from a production system as soon as they are observed.
 Dispose of dead fish properly to prevent spread of disease.

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 Use good sanitation practices resulting in clean equipment, ponds, and tanks. Disinfect containers,
nets, and equipment to minimize transmission of parasites and disease from one population to
another.
Controlling Measures:
1. Through Pond Cleaning and Disinfection:
 Bleaching powder (chlorinated lime) should be applied at the rate of 50 ppm in the pond.
 It readily kills all the wild fish species, molluscs, tadpoles, crabs and disinfects pond soil and water.
 In nursery and rearing ponds, it is desirable to use malathion at the rate of 0.25 ppm 4-5 days prior
to stocking of fish seeds.
2. Disinfection of Appliances:
 Nets, gears, plastic wares and hapas should be sun-dried or immersed in a disinfected solution.
3. Disinfection of Fingerlings and Feeding Platform:
 Disinfection with mild concentration of potassium permanganate solution is helpful during the
transfer of the fingerling to stocking tanks.
 The feeding platform can be disinfected by hanging bleaching powder cloth bags with mixture of
copper sulphate and ferrous sulphate (ratio 5:2) near the feeding place.
 When fish come to the feeding place for feeding purpose, their skin will be automatically
disinfected.
4. Proper Feeding:
 Fixed quality, quantity, time and place have to be followed for proper feeding.
 Any reduction in quality and quantity and variations in feed application and place may cause not
only deficiency disease, but also will increase the susceptibility to many infectious diseases.

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5. Segregation of year class fish population:
 Brood and older fish may serve as carriers of disease causing organisms without exhibiting any
clinical symptoms.
 To avoid such risk, young fish should be segregated from the brood and older fish.
6. Spot removal of dead fish from the pond:
 Dead and sick fish should be removed as soon as it is located.
 The daily loss of fish should be recorded to provide valuable insight to the intensity of disease
problem.
7. Chemoprophylaxis:
 Effective and inexpensive prophylactic measures against wide range of parasitic and microbial
diseases are advisable as chemoprophylaxis.
 Occasional pond treatment with potassium permanganate at the rate of 2 -3 ppm and dip treatments
with potassium permanganate at the rate of 500 - 1000 ppm for 1-2 minutes or short bath in 2-3%
common salt solution is safe.
8. Immunoprophylaxis:
 Immunisation programme is gradually emerging as one of the most important measures for
preventing infectious disease.
 Vaccine against Aeromonashydrophila, Plexibactercolumnaris, Edwardsiellatarda, E.ictaluri,
Aerononassalmonicida, Yoreiniaruckeri, Vibrio angullaramand several viral pathogens such as
IPNV (Infectious Pancreatic Necrosis Virus). CCVD (Channel Catfish Virus Disease), VHSV
(Viral Haemorrhagic Septicaemia Virus), IHNV (Infectious Haemopoitic Necrosis Virus), etc. are
being tried on large scale..

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Conclusion:
Stress compromises the fish’s natural defenses against invading pathogens. When disease outbreaks occur,
the underlying stress factors, as well as the disease organism, should be identified. Correcting stress factors
should precede or accompany chemical disease treatments. A disease treatment is only an artificial way
of slowing down an infection so that the fish’s immune system has time to respond. Any stress which
adversely affects the fish will result in an ongoing disease problem. Prevention of disease outbreaks is
more cost-effective than treating dying fish.

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References:
1. https://www.petmd.com/fish/care/evr_fi_stress_in_fish
2. https://www.hartz.com/stress-in-fish-symptoms-and-solutions/
3. https://www.aqui-s.com/stress-in-fish
4. http://neospark.com/images/stressor.pdf
5. https://dosits.org/decision-makers/tutorials/effects/fishes-stress/
6. https://www.researchgate.net/publication/43246636_Emerging_Viral_Diseases_of_Fish_and_Shrim
p
7. https://www.omicsonline.org/open-access/a-short-review-on-infectious-viruses-in-cultural-shrimps-
penaeidaefamily-2150-3508-1000136.php?aid=58619