Fish Diseases Lesson 2

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Fish DiseasesLesson 2

• Factors Involved in the Outbreak of Disease

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Factors Involved in the Outbreak of Disease

• A susceptible host
• A virulent pathogen
• Proper environmental conditions

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1. A susceptible host

• Good diet and clean water supply
• Avoid introducing fish from another hatchery -
  Quarantine
• Hosts defense system

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Fishes Lines of Defense

• Mechanical - Skin, Scales and Mucus
• Physiological -
• White blood cells (Phagocytosis)
• Liver detoxifies chemicals from water
• Local Tissue reactions
• Immune system
• Active against bacteria, parasites viruses

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2. Virulent Pathogen

• Not all bacteria cause disease
• Some strains of known fish pathogens may not
  always cause disease
• Bacteria can become more virulent by being
  passed through a fish

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3. Adverse Environment

• Changes in environment
• Certain temps favor or hinder pathogen
• Facility design - tanks vs ponds
• Biological factors
• Hatcheries with well water vs surface water

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Critical Levels of Water Quality

• Oxygen
• Nitrites
• Ammonia
• Total Alkalinity
• Total Hardness
• pH
• Temperature

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Critical Temperatures

• Optimum varies with species
• Tilapia - above 21 C (70 F)
• Trout - 10-16 C (50-61 F)
• Catfish 10-30 C Optimum 25-30 C (77-86)

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Critical Temps for Pathogens

• Ichthyopthirius Multifilis (Ich)
• Most severe 20-22 C ( 68-72 F)
• Can occur down to 5 C
• Seldom above 23 C ( 73)
• Channel Catfish Virus (CCV)
• occurs above 23 C
• Enteric Septicemia (ESC) -
• 23-27 C (73-81)
• Aeromonas 25-30 C (77-86)

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Factors in Disease Development

• 1. Source of infection
• 2. Mode (method) of infection
• 3. Portal of entry
• 4. Virulence of the organism
• 5. Resistance of the host

Break the Chain
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Source of Infection

• Infected fish, dead fish , sick fish, carriers
• Infected fish eggs from carrier broodstock
• Contaminated water supply
• Contaminated Feed
• Man and his activities

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Mode of Transmission

• Through the water
• water with all the waste products from the fish
  make ideal conditions for pathogens to survive

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Portal of Entry

• Gills - parasites can pierce gills and bacteria
  can enter
• Skin - breaks in skin and mucus by parasites or
  handling
• Ingestion-Dont feed wild, uncooked fish

Break the Chain
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Virulence of Pathogen

• Varies by species of virus or bacteria
• Different strains
• Pass-through effect

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Resistance of Host

• Different than immunity
• Immunity is acquired by previous exposure to the
  infection
• Natural Resistance
• substances in the fish
• Non-specific

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Factors Effecting Natural Resistance

• White Blood cells
• Tissue integrity
• Nutrition
• Age of Animal
• Strain of species
• Temperature

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Resistance

• Does not mean that the animal cannot be infected,
  but that the host has the ability to subdue the
  pathogen to the point where it will not cause
  disease.

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