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