Fish DiseasesFish DiseasesLesson 2Lesson 2

Factors Involved in the Factors Involved in the Outbreak of DiseaseOutbreak of Disease

Factors Involved in the Factors Involved in the Outbreak of DiseaseOutbreak of Disease

A susceptible hostA susceptible host

A virulent pathogenA virulent pathogen

Proper environmental Proper environmental conditionsconditions

1. A susceptible host1. A susceptible host Good diet and clean water supply Good diet and clean water supply

Avoid introducing fish from another Avoid introducing fish from another hatchery - Quarantinehatchery - Quarantine

Host’s defense systemHost’s defense system

Fishes’ Lines of DefenseFishes’ Lines of Defense

Mechanical - Skin, Scales and Mucus Mechanical - Skin, Scales and Mucus

Physiological - Physiological - – White blood cells (Phagocytosis) White blood cells (Phagocytosis) – Liver detoxifies chemicals from waterLiver detoxifies chemicals from water– Local Tissue reactionsLocal Tissue reactions

Immune systemImmune system– Active against bacteria, parasites & virusesActive against bacteria, parasites & viruses

2. Virulent Pathogen2. Virulent Pathogen

Not all bacteria cause diseaseNot all bacteria cause disease

Some strains of known fish Some strains of known fish pathogens may not always cause pathogens may not always cause diseasedisease

Bacteria can become more virulent Bacteria can become more virulent by being “passed through” a fishby being “passed through” a fish

3. Adverse Environment3. Adverse Environment

Changes in environmentChanges in environment Certain temps favor or hinder Certain temps favor or hinder

pathogenpathogen Facility design - tanks vs pondsFacility design - tanks vs ponds Biological factorsBiological factors

– Hatcheries with well water vs surface Hatcheries with well water vs surface waterwater

Critical Levels of Water Critical Levels of Water QualityQuality

OxygenOxygen NitritesNitrites AmmoniaAmmonia Total AlkalinityTotal Alkalinity Total HardnessTotal Hardness pHpH TemperatureTemperature

Critical TemperaturesCritical Temperatures

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

(77-86)(77-86)

Critical Temps for Critical Temps for PathogensPathogens

Ichthyopthirius Multifilis (Ich)Ichthyopthirius Multifilis (Ich)– Most severe 20-22 C ( 68-72 F)Most severe 20-22 C ( 68-72 F)– Can occur down to 5 CCan occur down to 5 C– Seldom above 23 C ( 73)Seldom above 23 C ( 73)

Channel Catfish Virus (CCV)Channel Catfish Virus (CCV)– occurs above 23 Coccurs above 23 C

Enteric Septicemia (ESC) -Enteric Septicemia (ESC) -– 23-27 C (73-81)23-27 C (73-81)

Aeromonas 25-30 C (77-86)Aeromonas 25-30 C (77-86)

Factors in Disease Factors in Disease DevelopmentDevelopment

1. 1. SSource of infectionource of infection 2. 2. MMode (method) of infectionode (method) of infection 3. 3. PPortal of entryortal of entry 4. 4. VVirulence of the organismirulence of the organism 5. 5. RResistance of the hostesistance of the host

Source of InfectionSource of Infection

Infected fish, dead fish , sick fish, Infected fish, dead fish , sick fish, carrierscarriers

Infected fish eggs from carrier Infected fish eggs from carrier broodstockbroodstock

Contaminated water supplyContaminated water supply Contaminated FeedContaminated Feed Man and his activities Man and his activities

Mode of TransmissionMode of Transmission

Through the waterThrough the water– water with all the waste products water with all the waste products

from the fish make ideal conditions from the fish make ideal conditions for pathogens to survivefor pathogens to survive

Portal of EntryPortal of Entry

Gills - parasites can pierce gills and Gills - parasites can pierce gills and bacteria can enterbacteria can enter

Skin - breaks in skin and mucus by Skin - breaks in skin and mucus by parasites or handlingparasites or handling

Ingestion-Don’t feed wild, uncooked fishIngestion-Don’t feed wild, uncooked fish

Virulence of PathogenVirulence of Pathogen

Varies by species of virus or Varies by species of virus or bacteriabacteria

Different strainsDifferent strains

Pass-through effectPass-through effect

Resistance of HostResistance of Host

Different than immunity Different than immunity – Immunity is acquired by previous Immunity is acquired by previous

exposure to the infectionexposure to the infection

Natural Resistance Natural Resistance – substances in the fishsubstances in the fish– Non-specific Non-specific

Factors EffectingFactors Effecting Natural Resistance Natural Resistance

White Blood cells White Blood cells Tissue integrityTissue integrity NutritionNutrition Age of AnimalAge of Animal Strain of species Strain of species TemperatureTemperature

ResistanceResistance

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