bacterial diseases. esc and columnaris these two bacterial diseases are the most common and most...
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Bacterial Diseases
ESC and Columnaris
• These two bacterial diseases are the most common and most devastating bacterial problems in the commercial catfish industry.
• Estimated economic losses resulting from these diseases is millions of dollars
Enteric Septicemia of Catfish (ESC)
• Causative agent - Edwardsiella Ictaluri
• Gram Negative, rod shaped, weakly motile
• Thought to be obligate but can survive in mud for 90 days.
• Similar to Edwardsiella Tarda
Which fish can get ESC?
• Channel catfish most susceptible
• White catfish, brown bullhead, walking catfish are also susceptible
• Blue catfish can get it but are generally resistant
Which fish can get ESC?
• Esc has been isolated from some diseased tropical fish.
• Trout, salmon and tilapia have been experimentally infected but natural outbreaks have not been reported.
Clinical Signs
• Behavior
• Tail chasing or spiraling
• Star gazing (head up tail down)
• Stop eating
Clinical Signs
• External Signs
• Red and white ulcers– petecial hemorrhages (pin point size)– Raised pimples (buckshot appearance)
• Hole or lightened area on head
• Exopthalmia
• Swollen belly
External Signs
Petechial Hemorrhaging (Buckshot appearance)
Deteriorating Skull Cartilage
ESC “Hole in the Head”
Clinical Signs
• Internal Signs
• Clear - straw colored or bloody fluid in body cavity
• Mottled liver
• Petechial hemorrhages in muscle
• Intestine often filled with bloody fluid
Diagnosing ESC
• Look at behavioral and external signs
• Necropsy for internal signs
• Isolate bacteria from internal organs– run diagnostic tests– determine antibiotic sensitivity
Causes of ESC
• Combination – Pathogen - virulent Edwardsiella ictaluri– Stress– Environment - that favors rapid proliferation of
the bacteria
• Generally in the “ESC Window” 68 - 82 degrees F
How Does ESC Spread
• Enters through– Gut– Nares– Gills
• Transmitted through water• Transmitted by cannibalism• Transmitted by carrier fish, equipment and
birds
Treatment and Prevention
• Prevention by reducing stress– not always possible
• Nutritional supplements
• Winter Feeding
• Genetic improvement
• Vaccination
• Treatment with medicated feeds
Medicated Feed Treatment of ESC
• Romet 30 and Romet B– sulfadinethoxine and ormetoprim– Fed at recommended rate for 5 days– 3 day withdrawal period
• Terramycin– Fed at recommended rate for 10-14 days– 21 day withdrawal period
Economic Evaluation
• Need to make sure that treating the fish does not cost more than the fish are worth
Other Methods of Control
• Withhold Feed
• Wait for temperature change
• Vaccines
Causes of Columnaris
• Causative agent - Flexibacter columnaris– Gram negative, rod shaped and motile– Non Obligate - present in the natural
environment
• Stress - particularly in warm weather– Especially long term exposure to low levels of
toxic ammonia
Characteristics of the Disease
• Rarely occurs unless fish are stressed
• Most frequently occurs between March and October when water temperatures are above 59F especially in the 75 -85 degree range
• Can be external, internal or both
Characteristics of the Disease
• Chronic at lower temperatures and more acute at higher temperatures.
• Likely to reoccur if original stress is not removed
• All ages, sizes and species can be effected
Clinical Signs of Columnaris
• External– increase in thickness of mucous on skin– saddleback appearance– areas of gray or colorless skin leading to ulcers
and open lesions– grey/brown areas on the gills esp. at the tips– yellow colonies inside the mouth– frayed fins
Columnaris ColoniesUsing Skin & Gill Wet Mounts
Columnaris on Gills
Columnaris (Frayed fins, tail rot)
ColumnarisSkin Lesions Leading to Open Ulcers
Diagnosis
• External - Microscopic examination of skin and gill wet mounts
• Internal - Isolation of bacteria and identification proceedurs
Treatment
• Depends on whether the infection is internal or external
• External only - 2 to 4 ppm KMnO4
• Internal only - Terramycin
• Both - Terramycin