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” 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 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 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 Colonies Using Skin & Gill Wet Mounts

Columnaris on Gills

Columnaris (Frayed fins, tail rot)

Columnaris Skin 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 KMnO 4 Internal only - Terramycin Both - Terramycin