Life cycle of Protozoan parasite

Life cycle of Protozoan parasite
Ichthyophthirius multifiliis:
• It is the most pathogenic protozoan parasites of freshwater fishes.
• It is also referred as the ‘Ich’.
• It is the causative organism of white spot/ Ich disease/ Ichthyophthiriasis.
• is an ectoparasite.
• It is easily introduced into a fish pond by new fish or equipment which has been moved
from one fish-holding unit to another.
• When the organism gets into a large fish culture facility, it is difficult to control due to its
fast reproductive cycle and its unique life stages. If not controlled, there is a 100%
mortality rate of fish.
Symptoms:
 Minute white nodules that look like white grains of salt or sugar of up to 1 mm appear on
the skin, fins and gills.
 Each white spot is an encysted parasite.
 Affected fishes show irritation, erratic movement and restless with tendency to rub on
the sides.
 Infected fish have small white spots on the skin and gills and produce excess mucus, due
to irritation.
 Some cysts joining together to form irregular patches.
 Damage caused to the gill tissue of an infected fish can also reduce respiratory efficiency.

Pathology:
Epithelial tissue changes occur in the area where the parasite is lodged and
its dislodging causes the epithelial ulcers.
Morphology:
Cilia
Macronucleus

Prevention and control:
Prevention of exposure of fish to the parasites
Prompt identification of the disease if it
occurs
Treatment of infected fishes.
Applying quarantine method
Control:
7000-20000 ppm NaCl for pond treatment
Formalin
Potassium per manganate

Ichthyobodo necatrix
 It is the causative organism of freshwater Ichthyobodosis.
 It is an ectoparasite.
 It is usually attached on dorsal fins and tips of secondary
gill lamellae of infected fishes.
Symptoms:
 Small spots appear on the body
 It may fuse into a greyish-white film from increased
production of mucus
 The more intensely affected areas are reddened and
hemorrhagic
 Infected gills are pale and covered with mucus
 Loss appetite.
 Moribund fish rise to the surface and become sluggish and
dies.

Flagellum
Contractile vacuole
Cytostome
Nucleus
Flagellum
Morphology:
Pathology:
 Goblet cells are not seen in the epidermis
 Hyperplasia occurs in Malphigian cells
 Acute hyperplasia and fusion of secondary gill lamellae
 Clubbing of gill filaments
 Epithelial cells with parasites become necrotic and blood vessels collapse
with proliferation of mucus cells in clubbed filaments.

 Treatment of infected fishes.
 Applying quarantine method
Control:
 Formalin 166 ppm for 1 hour (Flash treatment)
 Nacl 100000 ppm for 15-30 mins
 Copper sulphate 500 ppm for 1-2 mins
 Ponds with infected fishes should be drained
 Should be treated with lime before restocking the new fish

Chilodonellosis
• Chilodonellosis is the important parasitic disease of carp during winter.
• The causative agents of this disease are Chilodonella cyprini,
Chilodonella piscicola and Chilodonella hexascha
• It infect gill, fins and body surface
• It causes great loss to the pond fisheries
Symptoms:
 The mass development of parasite causes a greatly higher production of
mucus and disturbances in the respiratory function of the skin.
 The fish is restless, rises to the upper layers of the water.
 Its entire body covered with the bluish-white coating, particularly in the
head region.
 A smear from the skin surface reveals numerous individuals of the
parasites
 Causes localized hyperplasia of the gill epithelium

Pathology:
 It causes localized hyperplasia of gill
epithelium, which later becomes more
generalized.
 Proliferating epithelial cells fill the spaces
between secondary lamellae, which may fuse
together and turn into a single mass
 Then the respiratory epithelium is covered by
the hyperplastic epithelium and then
drastically reduce the respiratory surface of the
gill.
Morphology:

Trichodiniasis
 The causative agent of this disease is Trichodina sp.
 They are common ectoparasites of both freshwater and marine fishes
 They infect fry, fingerings and adults of Indian major carps and Chinese
carps.
Symptoms:
 Colour of the tail turns pale and there is a cream coloured coating due to
excessive mucus secretion.
 Fry and fingerlings show spinning behaviour.
 Scales become slippery due to excessive mucus.
 Tinny blood spots develop on fins and body.
 Fish show abnormal behaviour and colouration.
 Infected fishes gradually become sluggish and lose weight and become
moribund.

Cilia
Denticle
Radial pins
Border
membrane
Morphology:

Gyrodactylosis
• The causative agent of this disease is Gyrodactylus
elegans and Gyrodactylus gracilis
• They attack the skin, fins and gills of fish
• They are commonly known as gill fluke
Symptoms:
 The colours of the infected fishes become pale
 The skin becomes more slimy and shows small blood
spots
 The fins becomes droop and fold and gradually become
torn
 Breathing is increased in frequency

Marginal hook
Anchor
Developing embryo
Morphology
 Should be follow quarantine methods
 Fry and juveniles should be disinfected before stocking
 Add Methylene blue to the pond water at 1g/10m3
 KMno4 at 2 ppm and 3-5 ppm
 NH4OH at 500 ppm for 5-15 minutes

Also read-
Dactylogyrosis
Diplozooniasis

Adults on the gills
of fish
Egg with an
oncomiracidium
larva
Free
oncomiracidium
After attachment to the gills of a
host the oncomiracidium is
transformed into the diporpa
larva.
Fusion of 2
diporpas on
the host;
Each diporpa attaches its
sucker ( VS) to the dorsal
papilla ( DP) of the other.
Life cycle of monogenetic Trematodes

Life cycle of Digenean Trematodes
 Clinostomum compalanatum and Clinostomum marginatum are
unsegmented flatworms of the class Trematoda and the order
Digenea.
 They are also called as yellow grub
 They occur frequently in the skin and the muscle of the freshwater
fish.
 Small cream coloured nodules or cysts ranging from pinhead size up
to 2.5 mm depending on their age
 The number of cysts may vary from 1-100 or more than
 They have an oval or round shape.
 The skin of the fish in reaction to the infection produces the cysts,
which contain worms.
 It may take 3 weeks to make clearly visible cysts after the infection
and 7 weeks to reach full size

Diplostomum pigmentata
 It is the causative agent of Black spot disease in fish.
 The affected fishes are adult, fry and fingerlings of
Indian major carps
 Small brown or black spots on several parts of body
and fins.
 More than 300 cysts may present in a single fish
 The specific sites of infection are skin and underlying
muscles
 Such spots are also occur in the eyes, the gills and the
mouth.

miracidium
egg
1st intermediate host (snail)
Free swimming cerceriae
Metacerceriae in 2nd
intermediate host fish

Diplostomum spathaceum
 They are also called as eye fluke
 They attack in the lens, humour (liquid) or
retina of the eye.
 The extent of the damage ranges from
cloudiness and rupture to blindness

Cestode parasites of fishes
• Cestodes are endoparasites of fishes
• Complete their life cycle involving two or more
hosts
• The can infect fishes either in larval and adult
condition
• A number of species which are parasites on
freshwater fishes particularly belonging to
Pseudophyllidea, Protocephallidea and
Caryophyllidea

Ligula intestinalis
 Popular fish tapeworm which may cause
heavy mortality
 Causative agent of the disease ligulosis
 The immature stage of this tapeworm Infect
cyprinid fishes

Proteocephalus ambloplitis
 Known as bass tapeworm
 Can cause serious damage

 The strobila is produced by the
development of new proglottids in the
neck region, so that the proglottids
most distant from neck are the
oldest.
 Proglottids nearest the neck is
usually male and those furthest away
are female.
 The life-cycle involve one or more
intermediate hosts, mainly various
invertebrates but sometimes small
vertebrate
e.g. Ligula intestinalis
Dibothriocephalus latus
Scolex
Neck
Strobila
Proglottid

Zoonosis
 Is any infectious disease of animals (usually
vertebrates) that is naturally transmissible to
the humans.

Clonorchis sinensis
 Is also called the Chinese liver fluke
 The causative agent of human opisthorchiasis.

Dibothriocephalus latus
Causative agent of human Dibothriocephaliasis

Pallisentis ophiocephali
 Common acanthocephalan worm of murrels.
 The definitive host is Channa striatus
Channa striatus
Mature egg
Acanthor
Acanthella
Juvenile with
proboscis

Stress and disease
Disease:
 Disease is defined as an abnormal condition of body and mind of an
organism which is expressed with certain symptoms
 Disease is the end result of the host due to interaction and interrelationship
of following 3 factors-
 Adverse environment
 Infectious agents (Pathogen)
 Susceptible host (fish, shrimp)
 Such adverse/unfavorable
environmental conditions of fishes
include crowding, temperature
fluctuations, Inadequate DO, rough
handling, creation of toxic gases,
sublethal levels of toxic materials etc.
 These adverse environmental
conditions create stress on fish

 The role of stress in the host-parasite-environment
interaction in human medicine has been expressed by
Dubos (1955)
‘There are many situations in which the microbe is a constant
and ubiquitous component of the environment but causes
diseases only when some weakening of the patient by another
factor allows infection to proceed unrestrained, at least for a
while.’
e.g. Facultative bacterial fish pathogens such as Aeromonas,
Pseudomonas are continually present in water supplies,
epizootics will usually not occur unless environmental quality
and the host defense symptoms of the fish also deteriorate
 H+P+S2= D

Stress, infection and disease
Host+ Pathogen+ Environmental factors
Weak and stress Stage I
Infection Stage II
Disease Stage III

Different types of stressors
Physical stressors-
Temperature, light, turbidity, sounds
Chemical stressors-
Poor water quality, pollution, Diet composition,
Nitrogenous and other metabolic waste etc.
Biological stressors-
Population density, Parasites and pathogen,
predation etc.

Factors producing diseases in fishes
A. Environmental Factors
1. Physical
 Temperature
 Light
 Turbidity: mechanical injury by suspended
particles
 Sounds
2. Chemical
 DO
 PH
 Pollution-mining wastes, mill wastes, sewage
pollution
 Diet composition
 Salinity
 Intoxications-Insecticides, pesticides, heavy
metal, DDT
B. Biological factors:
Population density
Predation
Pathogens and parasites
Phytoplankton bloom
Inducing agents

C. Hereditary factors
Tumours, albinism, deformities,
tuberculosis, dropsy
D. Glandular dysfunction
1. Pituitary dysfunction-gill
impermeability, suffocation
2. Thyroid dysfunction- decrease iodine
3. Liver dysfunction-metabolic
disturbances
4. Pancreas dysfunction-metabolic
disturbances
5. Sex gland dysfunction- reproductive
inhibition
E. Mechanical injury
F. Pathogenic organisms
G. Atypical cell growth
H. Dietary deficiency factors
1. Carbohydrate deficiency
2. Fat deficiency
3. Protein malnutrition
4. Vitamins
A-exophthalmia
B1- Loss of balance
B2- photophobia
D-lower haemoglobin
E- Anaemia
K- blood do notcoagulate
I. Procedural
Rough handling
Transportation
Stocking
Disease treatment

Physiological response of fishes to stress
 In medical usage, stress is the metabolic response of the animal to a
stressor
 Stress is a state produced by an environmental or other factor which
extends the adaptive responses of an animal beyond the normal
range or which disturbs the normal functioning to such an extend
that, in either case the changes of survival are significantly reduced
 A series of morphological, biochemical and physiological change
occur as a result of stress which are called general adaptation
syndrome (GAS).
 It is usually divided into three stages-
 An alarm reaction
 A stage of resistance (adaptation to the stress has occurred)
 A stage of exhaustion (adaptation has been lost because the stress
too severe or long lasting)

 These stages are characterized by a variety of physiological and
biochemical changes which are not species specific.
 Some physiological and biochemical changes are-
1. ACTH (adenocorticotrophic hormone) is released from the
adrenohypophysis
2. Stress hormones (Cortisone, corticosterone, epinephrine) are
released from the adrenal tissue
3. Na+ and Cl- retention increases
4. K+ excretion increases
5. Blood glucose level increases
6. Nitrogen metabolism increases
7. Thyroid output increases
8. Respiration rate increases, cardiac output increases, systolic blood
pressure rises

Host-parasite-environment relationship
 The actual initiation of disease in fishes is a complex
process which involves more than mere contact between
the host and the parasite.
 Host susceptibility, parasite virulence and environmental
factors must all interact.
 Faculatative pathogen e.g. Pseudomonas, Aeromonas,
myxobacteria etc.
 Obligate pathogens e.g. Aeromonas salmonicida, IPNV,
VHSV

PATHOGEN/PARASITE
Infectivity
Virulence
Pathogenecity
Viability
Strain
HOST
Species, age
Strain
Nutritional status
Physiological condition
DISEASE POTENTIAL
ENVIRONMENT
Temperature
Oxygen concentration
Alkalinity
Hardness
Season
Other parameters
Reaction of Host, pathogen/parasite and environment

Relation between stress and culture
Extensive-
 Disease of fish in culture system more or less similar with
the wild
 No fertilizer and feed input-little chance to create stressful
condition
Semi-intensive-
 Some amount of fertilizer and feed supplied
 High dose of fertilizer, improper diet composition can create
stressful condition
Intensive-
 Water quality and exchanging
 Improper amount of feed
 Introduction of infectious agents
 Proper sanitation

Defense against disease
Protective barriers
Mucus-
 Act as physical barrier that inhibits the entry of disease
organisms from the environment into the fish
 Act as chemical barrier because it contains enzymes
(lysozymes) and antibodies (immunoglobulins) which
can kill invading organisms
 Lubricates the fish which aids movement through the
water
 It is also help in osmoregulation
Scales and skin-
Act as a physical barrier which protects the fish against
injury

Inflammation-
A nonspecific cellular response to an invading protein
It is characterized by pain, swelling, redness, heat and
loss of function.
It is an protective response and is an attempt by the
body to wall off and destroy the invader
Antibodies-
These are specific cellular response which are
specifically formed to fight invading proteins or
organisms

Effect of stress on protective barriers
A. Mucus-
 Chemical changes in mucus decrease the effectiveness as a chemical barrier
 Stress hamper the normal electrolyte (sodium, potassium and chloride) balance
which hamper the osmoregulatory function.
 Handling stress removes mucus and disrupt the physical barrier
 Chemical stress ( disease treatment) damages mucus
B. Scales and skin-
Damaged by handling stress
C. Inflammation-
 Hormonal changes decrease the effectiveness of the inflammatory response
 In cold temperature, the killer cells of the immune system completely stop
their works
D. Antibody production-
 Temperature stress- A sudden decrease in temperature, impairs the fish ability
to quickly release antibodies against an invading organism
 Prolonged stress limits the effectiveness of the immune system

Mechanism of infection into disease
The net result of stress on fish is to bring about metabolic
changes by their physiological control systems which
are designed to aid in surviving the imposed stress
 An increase in blood glucose (hyperglycemia)
 A decrease in blood chloride levels (hyperchloremia)
 An increased number of circulating thrombocytes
 A decreased inflammatory response
 Decreased liver glycogen
 Decrease in serum protein
 Increased 17-hydroxycorticosteroid levels

Increased plasma thrombocyte levels provide a
more effective hemostatic mechanism
Increased fibrinogen help in tissue repair and
walling off local infections
Increase plasma protein (haptoglobin
fraction)serves to bind any haemoglobin released
as the result of red cell destruction
Thus iron is conserved and renal damage is
preserved.

 Increased levels of corticosteroid hormones, with
reticuloendothelial deficiencies, combine to reduce the
tissue response to microbial invasion and allow infections
to spread.
 Chronic stress significantly reduce the immune response
 Leucopenia develops due to the hyper-secreation of
adrenal corticoids
 Due to the direct action of increased 17-
hydroxycorticosteroids on cell membranes, the fragility of
lysosome (phagosome) is decreased. Thus, stress may
indirectly result in impaired phagocytosis.

 The non-specific response to invading microorganisms is
somewhat dependent on the nutritional state of the host
 Inanition is synergistic with bacterial infections but
antagonism can occur with virus and protozoa.
 Vitamin A, C or D deficiencies are usually synergistic to
infections
 B-complex vitamin and mineral deficiencies behave variably
depending on the host and infectious agent
 Vitamin C influences the production and maintenance of
repair tissue
The process infection into disease is thus seem to be a strong
function of the physiological state of the host and is actually
the sum of a complex series of metabolic interactions
between invading microorganism and host-defense
mechanism

The influence of parasite on its host
• Every parasite living on or in fish exerts some degree of harmful
influence on its host i.e. changes in individual organs or tissues.
• Pathogenic and non-pathogenic
• However, every parasite is harmful to its host
• Sometimes, non-pathogenic parasites show a strongly pathogenic
character
e.g. Dactylogyrus minutum, a small and allegedly harmless
monogenean infesting the gills of the carp, occurs only in small
numbers in natural waters but it is capable of prolific reproduction in
aquaria, where it might cause the death of its host
• Parasite can influence the body of the fish in many different ways.

Mechanical effects:
 Damage to the tissue
 Rupturing of the protective layers
 Complete or partial atrophy of the internal organs
 Obstruction of the alimentary canal or vascular system
 Mass infestation of the skin with ectoparasitic Protozoa (Ichthyobodo,
Chilodonella and Trichodina) or monogenetic trematodes
(Gyrodactylus) causes excessive mucus. This coating or mucus
disturbs the respiratory function of the skin and ionic exchanges of the
blood
 Cause serious mechanical injuries to the gills and the walls of the
branchial chamber.
 Injuries, epithelial hypertrophy and an abnormally high production of
mucus occur at the point of attachment of many monogeneans,
causing disturbances in the respiratory function of the gills.
 Cause the partial or complete castration to the reproductive glands.
e.g. Ligula

Toxic effects:
 Parasite have toxic effects on their fish hosts
 These effects can be divided into two groups-
 Due to secretions of special poison glands
 Due to metabolic activity of the parasite
e.g. The mouth armament of Argulus includes a poison gland, the
secretion of which may kill small fish in cases of mass infestation.
 Parasitic toxins might influence the endocrinology of the fish.
e.g. The result of disease ligulosis is a considerable lowering in the
production of gonadotropic hormones and also the pathological
changes in the basophilic cells of the anterior part of that gland. The
underdevelopment of the gonads in ligulosis is due to the
mechanical suppression by the parasite and also to the toxic effects
on the glands

Consumption of the host’s food:
 When the parasites are comparatively large or occurs within the host in
great numbers
e.g. Eubothrium crassum
Parasites as vector of other parasites:
A parasite is sometimes harmful not only due to its own activity but also
because it disseminates agents of some infectious and parasitic diseases
e.g. the common leech, Piscicola geometra, is a vector of Trypanoplasma
cyprini
Parasites as a indirect causes of diseases:
By damaging the surface of the body and internal organs of fishes and
producing various wounds and ulcerations, parasites favor the penetration of
other pathogenic microorganisms, mainly fungi and bacteria.
e.g. Great concentrations of Ichthyobodo necatrix and Saprolegnia have been
observed around wounds caused by the copepod, Lernaea

The influence of infestation of non-specific sites:
 Generally all the parasites inhabit a specific site within their hosts.
 But sometimes parasites infesting the other organs in where he are
not adapted for living and do not cause any observable changes in
it
e.g. The parasites which are found in kidneys of Rutilus rutilus, are also
infest in the gut without causing any observable changes in it
The influence of parasite on the growth rate and condition of
fishes:
e.g. mass infection of Ergasilus sieboldi in fish
The influence of parasite on the size of fish populations:
The density of fish populations might be considerably affected by
parasites, particularly in the event of mass mortality
e.g. Ergasilus sieboldi causes 100% mortality of Tinca tinca in the
infested ponds

Reaction of the host fish
Cell and tissue reactions:
Hypertrophy:
• Hypertrophy is the increase in size of an organ or tissue due to the enlargement
of its component cells
• This response very frequently evoked by the penetration of the parasites,
particularly small one.
• Abnormal stimulation of the cellular mechanism leads to gigantism of the infected
cells
• Poorly specialized tissues, such as epithelium and connective tissue, are best
suited to this type of reaction
e.g. the hypertrophy of gill epithelium due to infestation of various species of
Dactylogyrus
Inflammation:
• Inflammation is a localized physical condition in which part of the body becomes
reddened, swollen, hot, and often painful, especially as a biological response of
body tissues to harmful stimuli, such as pathogens, damaged cells, or irritants.
• The reaction to the presence of parasite is often expressed by the process of
inflammation
• Inflammation develop at the point of penetration or at the sites of permanent
localization of the parasite
• Very often a connective tissue capsule is formed around the parasite, more or
less isolating it from the surrounding tissue.
• The body of the fish responds to all types of injuries by a more or less definite
process of inflammation.

Metaplasia:
 Metaplasia is the abnormal changes of tissues in their structure and function
 The tissues of the host respond to the presence of the parasite by
metaplasia
e.g. Mucoid transformation of epithelial tissue in fish when they are infested
with Chilodonella and Trichodina, Gyrodactylus. Epithelial tissues of fishes
contain single cells or group of cells which secrete mucus. Harmful influences
on the epithelial tissue result in the appearance of increasing numbers of such
cells
Immunity:
 The ability of the host to resist infection by the pathogen of a definite
disease.
 Acquired immunity in parasitic diseases is only partial, not totally preventing
but diminishing the chances of reoccurrence.
 It can affect retardation of development and of fertility of the parasite

Snieszko’s disease production equation by
interaction of environmental factors
H(A+S2)=D
H= Host
A=etiological agents
S= environmental stressors
D=Disease

Symptoms of the stressed fish
 Fish run erratically in the surface of the water
 Fish stays near the surface gasping for breath
 Fish would not eat, or does not eat as aggressively as past
 Changes color
 Rapid breathing
 Gulfing to the surface
 Jumping out of the water
 Motionless, sluggish and can stay in a standstill position
 Fish stays hidden continuously and would not come out where it can be
seen.
 Fish has nicked fins, open wounds that don’t seem to heal
 The mucus of fish skin is less or extreme

Changes in fish during stress condition
 External changes
 Internal changes-
Hormonal changes:
Excess excretion of adrenaline hormone
Increasing the rate of sugars in blood
Rising of blood pressure
Metabolic changes:
Significant increase of blood glucose
Hyperglycemia accelerated the raising of temperature and
blood glucose disturbance
Osmotic changes:
Induce the mechanism of osmoregulatory disturbances
Create water and mineral imbalance

Stress
Adrenaline
Fish
Water Diffusion
Fresh water
Water inhibition
Gain of weight
Hemo dilution
Sea Water
Loss of Water
Loss of weight
Hemo concentration
Fig.: Interpretation of some stress effects on osmotic balance

Stress mediated fish diseases
Diseases Predisposing environmental factors
Columnaris Crowding, handling, seining, adverse
temperature and infectious disese
Bacterial gill disease Crowding, unfavorable environmental
conditions, presence of bacteria, elevated
ammonia and particulate matter in water
Cold water disease 10 to 15°C – 7 to 13°C
Motile Aeromonas Septicemia Injury to skin, fins and gills, excessive
handling, low oxygen, pesticides,
crowding, improper nutrition

Prevention of stress
Good Management
Good water quality
Handling and transportation
High quality diet
Proper sanitation
Prevention of disease

Diagnosis
 Diagnosis is the art of determination of the nature of the cause/ causative
agent of the disease and problems assigned by the disease
Importance-
 For proper health management
 Detect the possible cause of disease and take the possible measures to
protect the fish stock from disease appropriately
 To prevent and control of fish disease
Diagnosis can be performed by two methods
1. Primary or gross diagnosis
2. Laboratory diagnosis
Primary or gross diagnosis-
 Fishes are diagnosed by observation of its external features, clinical signs,
physiological change etc. without laboratory tests

Visit the pond site:
 Basic pond site information
 Water supply details
 Production cycle
 Stocking density
 Feeding
 Waste disposal
 Diseases and other problems
To check the environment:
Physical parameters-
 Temperature
 Pollution-Affects the nervous system of fish
 Turbidity-Respiratory problem and mechanical injury
Chemical parameters-
 DO
 pH of water
 Presence of insecticides, pesticides, heavy metals etc.
Biological parameters- Presence of phytoplankton and zooplankton

O X
y
Mortality(%)
Days
Stage I (Due to toxicity of pathogen)
Stage II (Due to infection)
Stage III (Due to stress, nutritional factors
or environmental factors)
Checking of fish by sampling:
Changes in appearance and behaviour
Prevalence of diseased fish-
Incidence of infection-the percentage of fish infected in a population
Prevalence of disease = Percentages of diseased fish/ Percentages of fish
Fish Mortality Pattern

Difference between healthy and
diseased fish
Changes in behaviour
Changes in color
Fin disorder
Skin disorder
Gill disorder
Locomotion disorder
Physical changes

Observation Healthy fish Diseased fish Possible causes
Swimming Easy
movement in
water
Disturbance in locomotion
such as-
Jerky swimming
Movement in a small circle
Jumping movement
Fin and tail rot disease
Swim bladder stress
syndrome
Nutritional disease
Eye disease
Nutritional disease
Normal Swimming on side and
exposing ventral side to the
surface
Swim bladder stress
syndrome
Gas bladder disease
Don’t show
rubbing
activity
Rubbing bodies against
bottom or sides of container
or with hard objects
External protozoans
External crustaceans
Argulus sp.
Feeding Show
normal
appetite
Reduction of feeding
activity
Viral and Bacterial
infection
Poor water quality

Colour No dark
colouration
Dark body colouration over
the whole body
Viral disease-VHS
Bacterial disease
Nutritional deficiency
Normal
colouration, not
white covering
on the body
A hazy white covering over
the body
Columnaris disease
Fin Normal colour of
fin
Redness at the base of
their fins
Bacterial Hemorrhagic
Septicemia
Normal
appearance of fin
Fish’s fin appear to be
slowly eaten away and
edged in white
Fin and tail rot disease
Skin Skin with normal
slime
A slimy covering on their
skin in certain spots
Protozoan infestation
No cottony
appearance on
the skin
White thread-like or cottony
puffs on the skin
Infestation of
Saprolegnia

Gill Bright red
colour
Pale pink or white or
yellowish or brown
Viral, bacterial or trematode
infection
Excess nitrates in water
Fungal infection
Normal Gill clubbed and abroded External protozoans
Bacterial gill disease
Columnaris disease
Movement Normal Many fish active at
surface, gulping air
Lack of O2 in water
Protozoan gill parasite
Gill traumaNormal Many fish crowding water
inlet or crowding air supply
Abdomen Not
distended
Abdomen distended,
including oedema
Viral, bacterial or fungal
infection
Cestodes, nutritional imbalance
Eye Normal Exophthalmia Viral, bacterial or fungal disease
Protozoan parasites
Nutritional deficiency

Laboratory Diagnosis:
 By primary diagnosis, we know only whether the fish is diseased or
not
 One can find the specific pathogen which cause that disease or the
causative agent of the disease
 The laboratory techniques which are used for laboratory diagnosis-
A. Histopathological observation
B. Isolation and identification of pathogen
C. Pathogenic test
D. Rapid diagnosis

A. Histopathological observation
Histology-The study of structure and chemical composition of
animal and plant tissue
Pathology-The study which deals with the structural and
functional changes in tissues due to disease
Aim-
 To know about the structure of cells and tissue
 To separate the normal cells and tissues from abnormal
tissues
 To investigate the causative agents of the disease

Anaesthetization of fish
Collection of sample
Fixation (Formalin, Bauin’s fluid)
Dehydration (Methylated spirit)
Clearing (Xylene)
Infiltration (Wax or paraffin)
Embedding
Trimming
Sectioning
Staining (Clearing, rehydration) Drying and mounting (DPX, Canada balsam)

B. Isolation and identification of pathogen
Isolation
Viral cell-line culture/tissue culture
Bacterial Selective medium culture
Fungal-GP (Glucose-peptone) Agar medium
Identification
Based on characterization Bio-chemical
Physiological
Pathogenecity test, Virulence test

C. Pathogenic test:
 Pathogenic test is a method by which the fish is experimentally infected in
the laboratory.
 Experimental infection is possible through-
I. Immersion technique
II. Oral treatment
III. Intraperitonial injection
IV. Intramuscular injection
 Following test are used for pathogenic test-
Pathogenecity test/Challenge test-
Pathogenecity study of bacteria isolates to detect their pathogenic ability in fish
Virulence test-
Determine the degree of pathogenecity of the infectious organisms

D. Rapid diagnosis:
I. Immunodiagnosis-
 It is based on antigen antibody reaction
 Techniques of immunodiagnosis are-
Agglutination- 1. Slide agglutination
2. Microplate agglutination
FAT (Fluorescent antibody technique)-
1. Direct Fluorescent antibody technique
2. Indirect Fluorescent antibody technique
Blot technique- 1. Western blot, 2. Dot blot
ELISA (Enzyme Linked Immunosorbent Assay)
ELAT (Enzyme Labelled Antibody Test)

Immunoprecipitation (IP) or Radioimmunoassay (RAI)-
IP- the binding of antibodies to antigens in solution permits both the
purification of antigens
RAI- Identification/ quantification of antigens within a given sample
II. Immunohistochemistry
III. DNA Technique-
PCR (Polymerage Chain Reaction)
Molecular Biological Technique

Fish health Management
 Health-a state of harmony where all conditions of
organs i.e. physiological, metabolic condition etc.
are in well condition.
 Health management- Maintenance of proper
health condition of any organisms.
Fish health Management
Preventive measures Control measures

Prophylaxis
Prophylaxis is a measure taken to maintain health and prevent the spread of disease
There are two ways for prophylaxis of fish from infection.
1. Protection:
a. Provision of pathogen free water by:
i. Filtration: Prevent the entry of infective stage of larvae but inadequate to prevent the
entrance of microorganisms.
ii. Ultraviolet irradiation: The best effective method against micro-organisms in water
but cannot applied on large scale.
iii. Chemical treatment: Produced unsuitable environment & need experience to apply.
b. Provision of pathogen free food.
c. Hygiene of the fish farm:
i. Disinfection of the habitat by:
a) Disinfection of fish farms every 3-4 year Drying and added quick lime.
b) Dead fish must be removed.
c) Aquatic vegetation must be controlled.

d. Control of the wild fish.
e. Vector must be controlled (snails and birds).
f. Quarantine: Fish which are moved form suspected area or infected area to
non-infected area must be help in detention for a period of time at least
as long as the incubation period of the disease.
g. Regular prophylactic survey.
h. Random samples must be taken from fish farm for different examination
to ensure that the farms free from infectious diseases.
i. Independent water supply.
j. Age segregation.
ii. Disinfection of the equipments and utensils to prevent spread of
infection from one farm to another.
iii. Disinfection of fish twice yearly by:
a) Sodium chloride; b) Malachite green; c) Potassium per-manganate

2. Prevention:
a. Water:
fish need water that is not only pathogen free but also meets the
species-specific requirements of temperature, oxygen content
& purity.
b. Food:
fish must be provided with right kind of food with sufficient
quantity.
Nutrition deficiencies produced disease & also make the fish less
able to resist the pathogen.
c. Vaccination:
vaccination can be by injection, immersion, bath, spray & the oral
route.
The efficacy of vaccination is influenced by the quality of the
vaccine, the ability of the fish to develop immunity and the
conditions under which the fish are vaccinated.

Vaccination should be carried out under the following rules:
i. Do not vaccination diseased fish.
ii. Starve the fish for 48 hours before vaccination.
iii. Vaccine must be applied under aseptically condition as possible.
iv. When using the injection method, be sure to apply the vaccine correctly.
v. Vaccinate small number of fish & observe for a week before the rest of the
population.
d. Genetic manipulation to produce species that are resistant to disease.
e. Stress factors must be removed or avoided.
f. Population density: Accurate calculation of the number of fish /unit is
necessary. Suitable number of fish should be put in suitable unit to ovoid the
stress factors. Overstocking increase competition among individual fish
(10.000 to 50.000 fry per hectare).

Preventive measures
Pre-stocking measures
Stocking measures
Post-stocking measures

Pre-stocking measures
 Disinfection of hatchery and nursery
 Disinfection of different equipment such as container,
net etc.
 Maintain optimum level of water quality
 Control of weed and predatory fish and aquatic insects
 Controlling of undesired bush and branched trees of
ponds embankment for sunlight exposure
 Removal of excessive bottom clay
 Drying of old pond
 Application of appropriate dose of lime

Stocking measures
 Transportation of fingerling in well-oxygenated
disinfected and closed water container
 Applying of quarantine method for fry and fingerlings
before stocking
 Disinfection of fingerling before stocking
 Acclimatisation of fry and fingerling with pond water
 Maintain proper stocking density and species
composition of cultured species

Post-stocking measures
Removal of toxic gases periodically by manual
dredge on the pond
Applying feed in proper amount
Periodic checking of fish growth and health
condition by sampling of fish stock
Control on entry of birds, animals and insects
which carry fish pathogen
Periodic monitoring of water quality

Control measures
1. Test and slaughter
2. Quarantine and restriction of movement
3. Immunization and disease resistance
4. Destruction or reduction of intermediate host
5. Limitation or control of the release of toxic
substances
6. Systemic treatment
7. Hatchery sanitation
8. Drug therapy

Drug
 Drugs are chemical compound which have specific antagonistic
effect on the pathogenic agent causing disease
Major sources of drugs:
Medicinal value of drugs are obtained from-
 Mineral source- Iodine, Cobalt, Copper, Nickel, Iron etc.
 Animal source- Thyroid gland, pituitary gland, bones
 Vegetable/Plant/Herbal source- Roots, leaves, flower, seeds etc.
 Synthetic drugs- produced in the chemical industry
 Antibiotics- Antibiotics are chemical substances produced from
living cells of various microbes (bacteria, fungi etc.) that
suppress the growth and reproduction of other organisms and
may eventually destroy them without affecting the host’s tissue.
 Other sources-Alkaloids, fixed oil,Glycocoids, Resins, Tannins,
Volatile oils

Substances Used In Treatment
Substances which are used against fish disease in aquaculture of Bangladesh are
broadly classified as-
Antibiotics/ antibacterial agents:
About 60 antibiotics are available
Mode of action:
 Activates the enzyme which disrupt the bacterial cell wall
 Act directly on the cell membrane of microbes
 Affect the function of bacterial ribosome
 May be bacteriostatic or bacteriocidal
Uses:
Effective against common group of bacteria, fungus etc.
Terramycin
Streptomycin
Furacin
Oxilinic acid etc.

Antibiotics Water Food
Oxytetracycline 10-100mg/L 3.5 gr. /100 1b fish
/day
Erythromycin 4-8 mg/L 4.5 gr./1001b
fish/day
Chloramphenicol 10 mg/L 4 gr. /100 1b fish
/day
Sulphadimidine 0.025 mg/L ?
Penicillin 8000-12000 U.I/L 2.5 gr./100 1b
fish/day

Common drugs other than antibiotics
Malachite green:
Mode of action-
 Highly lipophilic.
 Bind to nucleic acid and exhibit RNA synthesis
 Distrub the production, performance of intracellular respiratory enzyme
Use:
 It is used against fungal infections especially Saprolegnia sp. Infections on eggs and fish
 Effective against white spot in combination with formalin
Dose:
 Pond treatment-0.25-0.30ppm once in a week for 3 weeks
 Bath treatment- 0.5-1 ppm
Sodium chloride (Salt, Nacl)
Formalin
Lime
Potassium permanganate (KMno4)
Iodine
Organophosphorus compounds
Methylene Blue

Herbal therapeutics
Neem
Action-
Effective against EUS
Dose-
After cutting the stem of neem into small pieces, the pieces are applied into the pond
Akanda
Action-
Effective against bacterial and fungal infection
Shotihalud
Action-
Effective against bacterial and fungal infection
Banana tree
Action-
It is used to reduce the alkalinity of water
Extracts of various types of tree and plant seed, roots and leaves
Action-
Having medicinal value for treatment of diseases

Therapy
 Therapy means treatment
 Is that process or phenomenon which deals with the treatment
of disease after its occurrence and which is applied to cure it
Types of therapy:
I. Chemotherapy or drug therapy
II. Herbal therapy
III. Surgical therapy
IV. Physiotherapy

Chemotherapy or drug therapy
 Chemotherapy is defined as a particular way or means of
preventing or correcting disease condition by using pure
chemical substances (drugs).
 Chemotherapy or drug therapy may be defined as the treatment
of disease by the use of drugs.
Principles of Chemotherapy:
 Chemotherapeutants seldom kill or completely eradicate all the
disease causing organisms
 They simply reduce the level of infection, prevents reproduction
or replication or retards the growth of pathogens.
 They dilute the toxins or harmful enzymes produced by the
pathogens

Herbal therapy
 Herbal therapy is the use of herbs i.e. bark, fruit, leaves, roots etc. of
natural plants, having medicinal value for treatment of the diseases
 It is specially used to control acidity and alkalinity condition of water
Surgical therapy
Usually surgical technique is used to overcome the disease i.e. removal of
tumor, necrosis etc.
Physiotherapy
It deals with the control or treatment by the physical means over the
various body organs
If growth of fish is hampered or disturb in swimming, then physiotherapy
is used

Drug therapy
 The treatment of disease by therapeutic agent or drugs
 Interplay of three factors-pathogen, fish and therapeutic agent or drugs
 Both the drug and the dosage must be carefully determined because many
therapeutic agent which kill pathogen, may have adverse effects on life
 Therapeutic agent or drugs should be-
 The difference between the lethal dose of the substance to the pathogen and to the
fish must be at least 1:4.
 Effective at low dose or concentration
 Cheap
 Easily available and easy to handle
 Safe for user, the environment and aquaculture organism
 Having no/less side and residual effect
 Easily soluble
 Minimum side effects on the productivity of the pond
 Rapidly biodegradable

General precautions before chemotherapy
 To know the common diseases in fish- I) Infectious disease
II) Non-infectious disease; III) Epidemic or non-epidemic disease etc.
 Gross diagnosis of disease
 Actual diagnosis of disease-to know the actual causative agent of
disease
 Where to apply- I)Open water ; II) Closed water
 To know the culture system-I) Polyculture; II) Monoculture
III) Extensive method; IV) Semi-intensive method; V)Intensive method
 To know about the fish-I) Species of fish; II) Age of fish; III) Size of fish
 To know the water-I) Volume; II) Water chemistry-alkalinity, pH and
temperature

 Stop the feeding of fish for 24 h before treatment
 Using plastic buckets for mixing the drugs.
 Ensure the proper dosages of drug
 Apply treatment during the day when the temperature is lowest
 Carry out a trial for treatment on few fish as control before making the
treatment on large scale.
 Wait 12-24h after the trial treatment
 Watch the fish continuously during treatment and be ready to interrupt
proceedings
 Only repeat the treatment if absolutely necessary but after 30h

Techniques of drug treatment
1. Addition of chemicals to water
A. Flowing treatment- To apply the required concentration of the drug in the
water by adding it continuously in predetermined quantities over a definite
length of time e.g. Formalin
B. Flushes- Diluted chemicals are added at intervals to the water intake
C. Dispensing the therapeutic chemical from a boat
D. Spraying
E. Hanging baskets
F. Bath- small, confined and easily controlled volumes of water
 Dips-less than 5 minutes. Lysol dip in 0.2% or 2000ppm for 5-15 seconds, is
used to control ectoparasitic Protozoa and Gyrodactylus
 Short baths- 5-60 minutes and concentration of the used chemicals are less
than the dips.
 Long baths-treatments for longer period in a low concentration of chemical
solution. e.g. Quinine baths (for ectoparasitic protozoa), DDT baths (for
crustacean parasites)

2. Addition of chemicals to feed:
Advantages-
used to treat the endoparasites
Less substance is required for feed additives
Causes less environmental pollution
Disadvantages-
Fish tend to stop feeding as a result of infection.
Even if they eat feed, it is not easy to ensure that
they will ingest enough medication to produce
the desired effects

3. Application of medication directly to fish
A. Injection:
There are two common places to inject into a fish.
a. Intraperitoneal injection (within the body cavity)-the ventral (bottom) part of the
fish behind either the pelvic or pectoral fin.
b. Intramuscular injection (within the muscle) are the dorsal (upper) part of the
fish above the lateral line and below the anterior part of the dorsal fin.

B. Oral or anal introduction of medication-
By syringes of suitable sizes and plastic catheters
C. Swabbing and dusting-
Swabbing is the application of a therapeutic liquid to the affected
area of the skin by painting it with a swab or brush
Dusting is the application of a powdered insoluble solid to the
affected fish either liberally sprinkled with the powder or rolled in
it.
e.g. Talcum powder for eradication of Argulus

Mode of transmission of fish diseases
Vertical transmission:
Pathogens are transmitted from one or both parents to offspring
through sex cell which for offspring.
Horizontal transmission:
the spread of the pathogen from one individual to another through
direct contact, air, or water.

1. Direct contact:
The etiological agent is transmitted from disease fish to healthy one. When both
infected and healthy fish are found in the same pond or when both fish are
moving in a restricted to obtain the natural food stuffs or moving for artificial
feeding.
2. Indirect contact by:
a. Migration of fishes: In natural water resources as rivers, lakes, seas, the
infection is transmitted through migration of infected fish, either during laying
egg in breeding seasons or during spawning.
b. Water: May act as mechanical carrier. The infection is transmitted form
one to other through water (up to down stream).
c. Soil: Many pathogens of fishes are kept alive and active in the bottom of
the ponds especially when it contains high amounts of organic material. e.g.
Aeromonas salmonicida and Saprolegina spp.

d. Feeding stuffs: Transmission of the disease also occurred through
infected feeding stuffs. This occurs when the meat of infected fish used
as sources of protein for artificial feeding of fishes. e.g. furunculosis or
bacterial kidney disease.
e. Egg: Some of fish diseases are transmitted though egg such as
bacterial kidney disease, viral haemorrhagic septicemia and
furunculosis.
f. Aquatic birds: Play on important role in spreading of fish diseases
especially parasitic diseases.
g. Tools and fishing articles: The transmission of the disease may
occur also by using contaminated and fishing articles during
transportation, catching of the fish or carrying it from one pond to
another.

Types of infections in fish diseases
1. Primary infection:
a. Simple infection: It is the infection, which caused by one
causative agent, e.g. bacterial kidney disease.
b. Mixed infection: It is the infection, which caused by two or
more infectious agent, e.g. infectious dropsy of carp.
2. Secondary infection: In which the primary infection considered
as predisposing factors, which help the appearance of another
infection. Presence of protozoa infections such as Costa leads
to appearance of motile haemorrhagic septicaemia.

Bacteria
 Any of the unicellular prokaryotic
microorganisms that commonly multiply by
binary fission and whose cell is typically
contained within a cell wall

Classification of Fish Pathogenic Bacteria
1. Gram-positive bacteria:
a. Cocci:
i. Staphylococcus epidermis.
ii. Streptococcus spp.
b. Rods:
i. Aerobic
a) Renibacterium salmoninarum.
b) Lactobacillus spp.
c) Mycobacterium spp.
d) Nocardia spp.
ii. Anaerobic
a) Clostridium botulinum
b) Eubacterium spp.
2. Gram-negative bacteria:
a. Aeromonas group
i. Non-motile Aeromonas
a) Aeromonas Salmonicida spp.
ii. Motile Aeromonas
a) A. Hydrophila
b) A. Caviae
c) A. sobria.
b. Enterobacteriaceae
i. Yersinia ruckeria
ii. Edwardsiella tarda.
iii. Edwardsiella ictaluri.
iv. Proteus spp.
c. Pseudomonas group
i. Pseudomonas angilliseptica
ii. Pseudomonas fluorescens.
iii. Pseudomonas chlororaphis.
iv. Pseudomonas putida.

d. Vibrios
i. Vibrio anguillarum.
ii. V. cholerae.
iii. V. Carcharie.
e. Photobacteria
i. Photobacterium damselae subsp. piscicida.
ii. Photobacterium damselae subsp. damelae.
f. Cytophagceae or yellow pigmented bacteria
i. Cytophaga
ii. Flexibacter
iii. Flavobacterium

Major bacterial diseases in aquaculture
Motile Aeromonas Septicemia
Columnaris disease
Edwardsiellosis
Furanculosis
Bacterial Haemorrhagic Septicemia
Bacterial gill dusease
Bacterial diseases in marine fish-
Columnaris disease-Flavobacterium maritimus
Bacterial cold water disease
Bacterial kidney disease
Mycobacteriosis
Edwardsiellosis
Vibriosis

Motile Aeromonas Septicemia (MAS)
 It is acute or subacute or chronic infectious disease of all freshwater fishes
caused by motile aeromonas bacteria, characterized by rapidly fatal
septicemia with few gross signs, exophthalmia, ascitis and ulcer formation.
 Also called as Haemorrhagic septicemia, infectious dropsy, infectious
abdominal dropsy, red pest, red disease, red sore
Distribution:
World-wide in fresh and brackishwater, specially Asia, Europe and the US
Susceptible species:
 Most cultured and wild fish are susceptible to infection with A.hydrophila
such as carp, channel catfish, eel, goldfish snakehead fish, rainbow trout,
brown trout and tilapia.

Etiology:
 This disease is caused by motile Aeromonas groups.
 Aeromonas hydrophila, Aeromonas caviae and Aeromonas sorbia.
 All motile aermonads are gram negative, motile, non-spore-forming.
 The optimum growth temperature is 28oC, but growth can occur at 37oC.
 Colonies on nutrient agar are white to pale pink, round and convex, with entire margins.
 It is a facultative anaerobe, fermenting carbohydrates to acid or acid and gas.
Epizootology:
The etiological agent is transmitted horizontally i.e. transmission from fish to fish via water
1. high temperature.
2. overcrowding.
3. reduction of oxygen.
4. malnutrition.
5. heavy infestation with parasites.
6. organic pollution.
7. high ammonia and nitrite level.
8. injuries or damage of the skin and gills.
9. rough handling and transportation of fish.

Pathology:
1. Acute form:
 Exophthalmia
 reddening of the skin and accumulation of the fluid in the
scales pockets and the abdominal cavity.
2. Chronic form or ulcerative form:
 dermal ulceration with focal hemorrhages and inflammation.
 Both dermis and epidermis are eroded and
 the underlying musculature becomes severely necrotic.
 Also severe tail and fin rot showed on the infected fish.
Histopathology:
 Necrosis of renal and spleen hematopoietic tissues, intestinal
mucous membrane, liver and pancreas
 Severe edema of dermis from skin lesions

Prevention:
Improve pond management system and follow the quarantine method
Reduce over crowding
Prevent the mixing of water from other pond specially polluted water
Disinfected net and equipment should be used
Control:
Oxytetracycline- 50-60 mg/kg body weight
Sulphamethoxazole- 60-70 mg/kg body weight
Oxilinic acid - 2-5 mg/kg body weight (oral treatment)
KMno4 -3-5 ppm in the pond
Diagnosis:
Definitive diagnosis by Isolation and identification
Primary isolation on BHA or TSA at 25-30°C.

Columnaris disease- caused by Flavobacterium
columnaris

Furunculosis
 Furunculosis is an acute, subacute, chronic or latent disease, primarily among
salmonid fishes characterized by formation furuncle or boil-like lesions in various
tissues of the body.
Etiology:
 The disease is caused by gram-negative, short bacilli called Aeromonas salmonicida,
which is classified into two strains.
1. Typical A. salmonicida, isolated from salmonids only.
2. Atypical A. salmonicida, isolated from salmonids & non salmonids species
 It is aerobic but is capable growth as facultative anaerobe and not spore-forming.
 Non-motile A. salmonicida produce brown-pigment on culture media as trypticase
soya agar, furunculosis agar and brain heart infusion agar.
 The microorganism was isolated from skin lesions, liver, Kidney and blood of infected
fish.
 Colonies develop within 48 hours at 22-25 °C as small circular, raised and
translucent. Colonies will not grow at 37°C.

Susceptible species:
All species of the family salmonidae are considered to be susceptible to furunculosis. A.
salmonicida has been isolated from fishes other than the salmonids such as carp,
catfish, and other fish species. Young fish are more susceptible to the disease than old
fish.
Epizootology:
1. Physical damage of the skin or gills.
2. Poor water quality.
3. Presence of ectoparasites and other diseases.
4. Both smolting and high temperature.
5. High stock density.
6. Rough handling
Mode of transmission:
1. The infection was transmitted by ingestion of contaminated food.
2. Water was found to be vehicle for spreading the infection.
3. A carrier is important sources for the infection.
4. The infection occurs through eggs.
5. The infection may occur through injuries of the skin.

Pathology:
1. Per-acute form:
 rapid death of fish especially young fish
 severe bacterial septicemia
 poor Darkening of skin,
 rapid breathing and
 slight exophthalmia
 Cardiac damage is a possible cause of death.
2. Acute form:
 hemorrhagic septicemia, including body and vents.
 Skin lesions may be haemorrhagic patches along the side or on the dorsal
body surface,
 hemorrhages at base of fins.
 Darkening of skin and sluggishness in movement.
 Hemorrhages scattered over abdominal walls, viscera and heart.
 Soft and friable or liquefied kidney is observed.

 Enlarged spleen with round edges.
 Pale liver with subcapsular haemorrhages.
 Stomach & intestine may contain bloody mucous.
 Swim bladder is hyperaemic.
 Raised furuncles, which usually develop in the dermis due to localization of bacteria
rather than the hypodermis. Fish may die within 2-3 days.
3. Sub-acute and chronic form:
 mortality rate is low & more common in older fish.
 Slight darkening of skin,
 lethargy and congested blood vessels at base of fins.
 Slight exophthalmia
 fish may have pale or congested gills.
 The furuncle may be small and compact or large & soft.
 They contain dark red pus with numerous bacteria.
 The mature furuncle bursts leaving deep ulcer or healed furuncle may leave scar tissue.
 The furuncle may be found in liver, kidney and spleen.
4. Intestinal form:
 This form is associated with low mortality.
 Prolepses of anus and intestinal inflammation may occur.

Diagnosis:
1. Case history.
2. Clinical signs and postmortem findings.
3. Isolation and identification of the causative agent.
4. Serological identification of the etiology by:
a. Agglutination test.
b. Precipitation test.
c. Fluorescent antibody technique.
d. ELISA.
Treatment/ Control:
1. Sulfamerazine: 150-220 mg/kg fish weight/day for 10-14 days.
2. Oxytetracycline: 50-75 mg/kg fish weight/day for 10 days.
3. Furazolidone: 25-100 mg/kg fish weight/day for 10 days.
4. Oxolinic acid: 10-mg/kg fish weight/day for 10 days.

Prevention:
1. Test and slaughter.
2. The pond is drained and bottom disinfected with quick lime.
3. All utensils used around the fishes and equipment must be disinfected.
4. Transportation of fishes from infected areas to other must be prevented.
5. Fish eggs should be obtained from fishes free from pathogen.
6. Movement of the water stream from infected area to non-infected must be
prevented.
7. Immunization of fish against A. Salmonicida has been studied. Laboratory
result indicated that fish can produce protective antibodies against the bacterium.
(Formalin killed bacterial & mineral oil adjuvant).
8. Stress factors must be removed.

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