Fish Diseases

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PRINCIPLES OF AQUACULTURE(AKU3201)

• Fish Diseases

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Factors affecting fish health

• Host Environment
• - Stocking density - Poor sanitation
• Handling - Changes in pH, salinity
• - Transport temperature etc.
• Chemotherapy
• Nutrition
• Behaviour
• Disease agent
• Pathogen/ non-pathogen
• Opportunistic pathogen

Disease agent
Disease
Env
Host
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1) Host susceptibility

• Physical barrier (skin, scales, exoskeleton,
  shell, mucous membranes)

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Behavioral Signs Failure to feed
properly Flashing (turning on their
sides) Rubbing on the bottom Gathering around the
water inflow Reduced vitality Gasping at the
surface

• Physical Signs
• Blistered areas
• Swollen bellies
• Popped-out eyes
• Bloody (hemorrhaged) areas on fins
• Discoloration or erosion of body parts
• Excessive mucus
• Growths on the body

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• Physiological defences
• - Immune system, detoxification by liver
• Nutritional well-being
• Age (Young more susceptible)
• Spawners stress due to their reproductive
  functions

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Sick fish

• Unusual behaviour
• Scrap body to wall
• Coming to surface, gulping for air
• Erratic swim
• Loss appetite
• Physical changes

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Diseases

• Exophthalmia (Pop-eye)

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• Extended belly

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• Haemorrhage

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2) Environment

• Crucial role in disrupting the balance between
  host pathogen
• Environmental stress gt pathogen host react
• disease occur

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• Stress
• Anoxia absence of oxygen
• Fright
• Anaesthesia
• Temperature changes
• Injury
• Pollution

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• High stocking density
• Restricted spaces cages/tanks, raceway
• Large quantity of concentrated feeds/ fertilizer

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2) Environment

• Do not exceed carrying capacity stocking
  density
• Always monitor water quality
• Maintain proper DO, pH, alkalinity, temperature
• Check accumulation of organic debris, nitrogenous
  waste (ammonia, nitrite), hydrogen sulfide
• Remove pond bottom sludge, dry lime

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• Temperature changes fluctuation day night
• Poikilothermic
• Hatchery
• Closed system
• If temp. drops, used heater

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3) Disease agent

• Potential pathogens always present in aquatic
  environment

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Disease agent

• Parasites (cestodes, nematodes, trematodes
  protozoans)
• Bacteria (vibriosis, edwardsiellosis,
  furunculosis)
• Viruses (IPN, lymphocystis)
• Fungi (saprolegniasis, branchimycosis)

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• Common entry point
• 1) Wound in skin
• Bacteria/viral infections gt fungal infection
• 2)Gills
• Pathogen enter body through delicate thin
  epithelium
• Protozoa establish themselves on them
• 3) Digestive tract
• Bacteria penetrate intestinal lining
• Protozoa

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1) Parasites

• Most common cause of fish mortalities
• Especially in larvae fingerling stages
• Multiply rapidly without intermediate host
• Attach themselves to the host special organ
  such as suckers

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• Penetrate host to multiply invade vital organs
• Invade through ingestion, skin rupture,
  transgression of gill lamellae, penetration to
  the egg membrane

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Protozoan Ichthyopthirius multifiliis
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Copepod Argulus, Lernaea
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Isopod (Sea lice)
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Monogenean parasites
Dactylogyrus
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Gyrodactylus
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Nematode
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2) Bacterial disease

• Vibriosis
• - Vibrio harveyi

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• Vibrio anguillarum
• Vibrio alginolyticus

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Quorum sensing
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2) Bacterial quorum sensing

• Monitor the environment alter
  behaviour

Quorum sensing (QS)
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2) Bacterial quorum sensing

• Signal molecules

AHL
(Found in 70 different G- bacterial species)
Diseases controlled by QS
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• Aeromonas
• Aeromonas hydrophila
• Aeromonas salmonicida

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Furunculosis
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• Edwardsillosis
• Edwardsiella tarda
• Edwardsiella ictaluri

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• How to identify bacterial isolates

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Cotton swab
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Biochemical test
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Molecular techniques
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Serology

• ELISA (Enzyme-linked immunosorbent assay)

Antigen Antibody Enzyme Sensitive method
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3) Viral disease

• Infectious pancreatic necrosis (IPN)

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Lymphocystis
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White spot
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4) Fungal disease
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Case study- Malaysia
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• Mass mortality June- August

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Spread of disease between country

• Import- export
• Exotic disease
• Stress during transport
• Fish weak susceptible to disease
• How to overcome
• Discourage/ ban import of live fish
• Quarantine sterilize the fish
• Purchase from reliable source
• Seed free from disease

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• Spread of disease in pond/cages
• Through water channel
• Spread pond to pond
• No barrier
• Water current
• Dead fish thrown into open waters
• Other animals as carrier
• Equipments

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Solution to fish disease

• 1) Integrated health management
• 2) Health inspection disease monitoring
• 3) Disease treatment
• 4) Sanitation
• 5) Immunization
• 6) Genetic resistance to disease
• 7) Farm disinfection

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1) Integrated health management

• Guidelines for prevention, control eradication
• Correction of disease-causing disease
  spreading conditions
• Adoption implementation of policies
  regulations by the state need cooperative effort

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2) Health inspection disease monitoring

• Always monitor record health status, water
  quality etc. corrective measures can be taken
• One trained person basic facilities to
  undertake regular health environmental
  monitoring
• - if expensive then twice a year inspection

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3) Disease treatment

• Chemotherapy temporary, effect on biofiter
• Antibiotic resistant bacteria
• Vaccines specific to certain fish

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4) Sanitation

• Maintain good sanitation
• Good culture practices
• Monitor water supply ozonation, UV, chlorination
• Egg disinfection

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• Quarantine
• particularly to prevent the introduction of
  communicable disease
• - Facilities located away from farm
• Need to disinfect all facilities chlorination

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5) Immunization

• Mechanism of antibody production
• Antibody specific immunoglobulin (modified
  protein) produced in response to reacts
  specifically with an antigen (foreign substance
  that stimulate the formation of antibodies)
• Vaccines contains antigens that are generally
  attenuated or killed disease agents. When
  administered to a host, they stimulate the
  production of specific antibodies or non-specific
  resistance to that particular disease agent

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• Vaccination
• Immersion small fish
• Spray-shower fish larger than 4g
• Injection intra-peritoneal
• Retain immunity 300 days

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6) Genetic resistance to disease

• Disease resistant strains through genetic
  breeding
• Select strains with disease resistant
• High level of genetic diversity hybrid vigour

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7) Farm disinfection

• Disease outbreak Farmer destroy stock
  disinfect rearing facilities
• Easier fro small, well-controlled facilities
  e.g., hatcheries, tank, raceways.
• Earthern pond difficult

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Special care during transportation

• During transportation
• Minimize physical injury use smooth net
• Avoid sharp edge tank
• Stop feeding 12-24h to reduce metabolism
  excretion
• Provide high oxygen level
• Salt at 0.3-1 to minimize osmotic stress
• Anesthesia if necessary
• Put bag into Styrofoam box
• Acclimatization- bag left floating for 30 minutes

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• Quarantine new fish check for pathogen
• Remove dead fish from system
• Dispose dead fish properly
• Good sanitation practices

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Ketapang leaves
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Improve water qualityo
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Biosecurity

• Biosecurity Steps taken to keep disease from a
  farm to prevent the transmission of disease
  within an infected farm to neighboring farm.
• Consideration on initial facility layout design
• Breeder gt hatchery gt growout (need to ensure
  biosecurity measures)
• Need to have SOP
• Isolation, sanitation control
• Closed system
• Open system?

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Biosecurity

1. Reduce the risk of disease introductions
2. Minimise the spread of diseases on-farm or to new
   areas
3. Promote fish health
4. Protect economic investment
5. Protect human health

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Biosecurity

• Avoid the introduction of certain pathogens into
  an aquaculture facilities
• Purchase from a producing selling certified
  specific pathogen-free (SPF) stock
• SPF special stock of animals that are kept in
  specific pathogen free facilities under rigorious
  monitoring system
• Problem Only few spp. of SPF e.g. shrimp
• Shrimp have primitive immune system
• No workable vaccine

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• d) Tilapia Pangasius no SPF but have vaccine
• e) Vaccinated Pathogen Free seed-stock (VPF)
• VPF Fish vaccinated when they are healthy
  before exposure to the nature
• f) Have own in house broodstock/spawning
  facilities
• g) Have a quarantine/ isolation facilities

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• 2) Provide a pathogen- free water source
• Mechanical filtration
• Chemical treatment
• UV filtration
• Ozonation
• Well- water
• Biological treatment

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Drum-filter filtration of suspend solids in
closed system
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Protein skimmer remove dissolved organic matter
in water
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• 3) Disease monitoring
• Always monitor for clinical signs of disease
• Regular scheduled health evaluation
• Sampled for diagnostic health techniques
• Treat if warranted

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• 4) Disinfection
• Strict adherence to cleaning disinfection
  techniques
• Foot bath hand wash
• Container with disinfectant for nets etc.
• Separate equipments (nets, feed bucket)
• Disinfect vehicles
• E.g disinfectant Hypochlorite
• Maintain good husbandry practices

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First chlorine, then thiosulphate to nuetralize
chlorine
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• Good aquaculture practices (GAP)
• Improved production, food safety assurance
  preservation of environments
• Hazard Analysis Critical Control Point (HACCP)
• Standard sanitation operating procedures (SSOP)

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SPLAM

• Malaysian Aquaculture Farm Certification Scheme
• Sijil Pensijilan Ladang Akuakultur Malaysia
  (SPLAM)
• Encourage Good Aquaculture Practice emphasize
  implementation of HACCP
• Aquaculture entrepreneurs need to fulfill
  requirements criteria set by DOF
• Make application, undergo a review audit final
  approval
• Valid for two years

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Objective SPLAM

• Official recognition to aquaculture entrepreneurs
  who have practiced GAP environmental friendly
  concepts

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