A
F
U
Common fish diseases
and parasites
Dilip Kumar Jha, PhD
Professor
Department of Aquatic Resources
Agriculture and Forestry University, Rampur, Chitwan
dkjha.ait@gmail.com 9845155154; 9804273475
A Common fish diseases and parasites
F
U
• Introduction, causal organisms, symptoms and
control measures of Saprolegniasis, Tail rot/fin
rot, White spot disease, Dactylogyrosis,
Argulosis; and Asphyxiation
A
Introduction
F
• Disease:
U • “A condition impairing the health”
• The inability to perform physiological function at
normal levels, provided the nutritional and
environmental factors are at an adequate level
• Diseased animals are not just sick or dying but
include even those which are performing below
expectations
A
Terminology
F
U • PATHOLOGY: is the study (logos) of suffering
(pathos) involves the investigation of the
causes (etiology)as well as the mechanisms
(pathogenesis) deals with the structural and
functional changes that result from disease
process
A
Terminology
F
• Pathogen: disease producing agent or micro-organism
U
• Pathogenesis: process by which a disease originates
and develops
• Pathognomonic: characteristic of a disease
• Pathologic: relating to disease
Terminology
A
• Necrosis: tissue dysfunction or even death (within a
F living body) occurring after the loss of blood supply or
after an exposure to toxins
U
• Inflammation: complex of changes in the vascular
connective tissues
– Sporadic: occurs in solitary manners
– Enzootic: exists among certain species
– Epizootic: affects a large number of fishes over a
wide area
– Exotic: disease of foreign origin
A
F
U
Terminology
• Acute: a severe cause of relatively short duration
• Sub-acute: Severity, duration and onset are less than
the acute
• Chronic: slow in onset, longer in duration. Not severe in
character
Specific: has a definite cause, definite identity and
does not contain merely a group of symptoms
• Contagious: spreads by direct contact
• Infectious: caused by microbes viz. fungi,
bacteria etc. It may or may not be
contagious. All contagious are infectious
• Non-infectious: various causes
A
Epidemiological Triad:
F
U • Germ theory
Disease agent +
Susceptible host –
Disease
Host
Agent
@DKJha
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A
F
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How does disease occur?
P=Pathogen
1
H+P+S2=D
Where,
H= Host
P= Pathogen
S= Environmental
Stress
D= Disease
1- 2- 3
D
E(S)=Environment
H=Fish
2
3
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Signs of sickness
A
F • Fish at surface of water become listless
• Refuses its usual food for more than 2 days
U • Fish gasping at the surface of the water
• Lethargic and doesn’t move around and pale gills
• The fins may be clamped to the body
• Fish's tail (caudal fin)or other fins appear frayed at
the edges or are breaking off and disappeared
• Fish scratching against rocks or sides of the tank
• Flashing (rolling over its bellies) the top of the water
• One or both eyes protrude from the head
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Saprolegniosis
A
F
•
Saprolegniosis
is
a
fungal
disease
and
also
U called as water mold or cotton wool disease
• Etiological agent: Saprolegnia parasitica
A
What are fungi?
F Fungi
•
Constitute
a
group
of
heterotrophic
organisms,
U which contain no chlorophyll and are
historically compared to plants.
• They are usually filamentous and multicellular,
although some are non-filamentous and
unicellular.
A The filaments known as hyphae (sing. hypha)
constitute the body of a fungus. These filaments
F elongate by apical growth (growth is active at hyphal
tips), in contrast to intercallary growth of other
U filamentous organisms.
The hyphae are either septate (divided by cross walls)
or non-septate (coenocytic, without cross walls). They
branch successively behind the tips, resulting in a
network of hyphae called mycelium (pl. mycelia).
Septa
Non-septate (a) and septate (b) hyphae
A
The Thallus
F • Most parts of the fungal body (also known as soma or
U thallus) are potentially capable of growth. A minute
fragment from most parts of the organism is able to
produce a new growing point, and to start a new
individual.
• In general, fungi reproduce by both asexual and sexual
means producing different kinds of spores as end
products. The reproductive structures are usually
differentiated from the somatic structures.
A
F
U
SAPROLEGNIOSIS
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A
Saprolegniosis
F Saprolegnia parasitica
• The fungi are normal water inhabitants that invade
U the traumatized epidermis. Improper handling,
bacterial or viral skin diseases, and trauma are the
major causes of the disease.
• Disease Signs
• Clinically, affected fish develop white to brown cotton like
growths on skin, fins, gills and dead eggs. This organism is an
opportunist that will usually grow over previous ulcers or
lesions
A
F
U
Disease Signs
• Saprolegnian fungi are opportunistic facultative
parasites.
• Diagnosis is by finding broad nonseptate branching
hyphae that produce motile flagellated zoospores in
the terminal sporangia.
Management and Control
A
is best prevented by good management
F • Saprolegniasis
practices--such as good water quality and circulation,
of crowding to minimize injury (especially
U avoidance
during spawning), and good nutrition. Once Saprolegnia is
identified in an aquatic system, sanitation should be
evaluated and corrected.
• Common treatments include potassium permanganate,
formalin, and povidone iodine solutions.
• Over treatment can further damage fish tissue, resulting in
recurring infections.
A
Control..
management is essential for satisfactory
F Environmental
resolution of chronic problems. Bath treatment in NaOH
U (10-25g/l for 10-20min), KmNO4 (1g in 100lit of water
for 30-90 min), CuSO 4 (5-10g in 100 lit water for 1030min).
Malachite green oxalate (zinc-free) treatment is still the
most commonly practiced at a dose of 0.1–0.2 ppm for
1 hour, or by continuous flow, to yield a final
concentration of 0.05–0.075 ppm for several days.
A
Bacterial Diseases
F
• Bacterial diseases often cause considerable damage in
U fish farming.
• Bacteria are single celled, minute organisms and are
found everywhere in nature.
• Pathogenic bacteria are almost always present either
in the surrounding water, on the surface of fish, or
within the fish where they may be present in the
intestine or other internal organs.
A
Tail rot/Fin rot
disease is due to bacterial infection and results in the
F • This
putrefaction of Caudal fin(Tail fin) or other fins.
U • Etiological agent: Flexibacter columnaris/Flavobacterium
columnare
• Disease signs: A more or less distinct white line is seen at the
margin of the fin in early stages of the diseases. This line
moves towards the base of the fin and the fin becomes torn
and after sometimes the entire fin is completely destroyed.
• Treatment: Dip treatment for 1 minute in 500 ppm CuSO4
solution. A bath in a dilute solution of Acriflavine has also
proved to be very effective against fin rot.
A
F
U
Fin rot
A
Protozoan disease
F • ICHTHYOPHTHIRIOSIS/White spot / Ich
U
• Ichthyophthirius multifiliis, commonly referred as
‘Ich’ is a ciliated protozoan parasite that infects
freshwater fish and causes “white spot disease”. It
has a significant economic impact on both food and
aquarium fish production.
• It parasitizes the epithelia/sub-epithelia of the skin,
fins and gills.
A White spot or Ichthyophthiriosis
F Causal Organism:
Ichthyophthirius multifiliis
U – Ciliated, Uniform ciliation
– Spherical or ovoid, round
– The nucleus is U- shaped
– Up to 1 mm in diameter
– Various sizes – trophs and invasive small pear
shaped tomites
– Cosmopolitan in distribution(Reported in Nepal in
1972)
A
White spot
•
Both
macronucleus
and
micronucleus
are
present.
F The micronucleus lies on the concave side of the
which is horseshoe(U)shaped and
U macronucleus,
controls vegetative functions.
• It is characterized by presence of
white spots all over the external
body surface.
• This parasite is very dangerous and often kills the
host.
A
F
U
A
F
U Diagram
showing Life
cycle of
Ichthyophthirius
multifiliis
1.Fish affected with Ich 2Trophozoite and Adult
mature parasite 3. Encysted stage 4. Tomites 5.free
swimming young stage liberating from tomites
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Control: The ponds should be drained and dried after an
F outbreak, then treated with quicklime for killing cysts.
The wild fish should be prevented from entry through
U water inlets.
Treatment of white spot disease is difficult because of
the variability of the time of completion of the life cycle.
Since the life cycle is not synchronized and no drug has
been found which kill encysted form that’s why
treatment must be prolong and repeated frequently.
The free-swimming phase is the best time to treat with
chemical.
A
Control and Treatment
F • Formalin: Daily bath 200-250ppm;
Pond treatment: 15ppm
U It has been reported that fishes in ponds are treated with
15 to 25 ppm while aquarium fishes are treated with
25 ppm on alternate days until the infection is cleared.
• Acriflavin: Bath 10 ppm 10-20 minutes
• Sodium chloride : 1.5 to 2.5% for 10 to 30 minutes/ 7
days
• Potassium permanganate: 2-5ppm for pond
treatment.It must be remembered that organic matter
reduces its potency.
Dactylogyrosis (Gill flukes)
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Etiological agent: Monogenean Trematode; Family:
F Dactylogyridae: Dactylogyrus vastator
U
Found only on the gills and manifest respiratory signs
Cultured freshwater and marine fishes are susceptible
Distribution: Cosmopolitan
• The dactylogyrids are never more than 2 mm in length
and most often between 0.2 and 0.5 mm(Dactylogyrus
vastator sizes ranges up to 1.1 mm)