Bacterial Diseases Enteric redmouth - ERM (Yersinia ruckeri) Furunculosis (Aeromonas salmonicida) Coldwater disease – CWD (Flavobacterium psychrophilum) Bacterial gill disease (Flavobacterium branchiophila) Bacterial kidney disease (Renibacterium salmoninarum) Strawberry disease

Yersinia ruckeri Enteric Redmouth Disease (ERM) “Hagerman Redmouth” primarily RBT Rucker - First reported in 1958 in Hagerman Valley. Named in 1978 Yersinia ruckeri

Host Range and Vectors North American outbreaks – possibly due to carrier fish or contaminated eggs from Idaho Sources - imported baitfish, ornamentals, bird feces, etc.

Clinical Signs ERM Chronic: Reddening in mouth and under operculum, and internally throughout peritoneum, intestine, and fat of the body

Y. ruckeri Obligate parasite Generally occurs 13° - 15°C Acute, sub acute, chronic forms

Yersinia ruckeri Non-spore forming, straight rod Motile with flagella No pigment, grows slowly at 8 and 35.

Carrier State Intestinal shedding of organism Stress conditions, carriers transmitted Y.r. to healthy fish but unstressed fish did not

Virulence of Y.r. Strain typing has been done widely (Hagerman – Type I)

Treatment and control Vaccines: First were Ross and Klontz 1965. JFRBC 22:713-719. phenol killed (in feed) First commercial fish vaccine: licensed by USDA in 1976 (formalin-killed whole cells) Single most effective management tool for control of mortality due to ERM.

Coldwater Disease Flavobacterium psychrophilium Bacterial cold-water disease - CWD First observed in Leetown WV in rainbow (peduncle disease) Next in 1948 in Washington - lesions near tail, and on dorsum

Host Range and Vectors Serious infections in salmonids worldwide - distributed widely across NA continent Has been linked to viral pathogens such as IHNV

Host Range and Vectors Free-living examples exist Resident salmonids likely carriers

Clinical Signs CWD Externally: rough appearance of skin and necrosis of fins May see open ulcerations on skin External or septicemic

Clinical Signs CWD Internally: Erratic/spiral swimming Development of deformities and/or nervous disorders

Transmission Natural reservoirs uncertain Mortalities increase when IHN involved Number one concern in Hagerman Valley

Diagnosis of CWD From clinical signs and necropsy Gram negative, Rods Gliding motility Growth best on low nutrient media

Treatment and control Extra-label use of antibiotics for control – somewhat effective (but resistance a potential problem) Vaccines

Furunculosis One of the oldest known bacterial fish pathogens Mostly associated with salmonids, but other fish can be infected Obligate pathogen (fish to fish transmission)

Clinical signs Acute - Adult, sub-adult, darken, stop feeding, hemorrhage base fins, internal hemorrhages Fingerlings - dark, dying

Clinical signs Chronic, focal dermal necrosis – BOILS Acute septicemia

Transmission Horizontal Dead fish/fecal material Mucus - asymptomatic carriers Sediments and associated biota

Presumptive Diagnosis Morphology, Stain, non-motile Non spore-forming rod (1 x 2 µm) Pigment forming non-motile

Treatment and control Antibiotics: Resistance can be a problem Vaccines:

Bacterial/environmental Gill Disease (Flavobacterium branchiophilum) Gill infections primarily in juvenile fish F. branchiophilum dominant bacterial species Found throughout North America and other countries

Clinical signs BGD Flared gills, lethargy, swim high in water column Gill lamellae fused/clubbed (poor oxygen transport) Debris and bacteria present Usually associated with poor environmental conditions or parasitic infestation

Diagnosis/control Diagnosis: Usually based on clinical signs (obvious) Test for specific bacteria Control: Improve environmental conditions (increase DO) Treat fish (various chemicals), 1-5% NaCl may be method of choice

Bacterial Kidney Disease Renibacterium salmoninarum Initially described in Atlantic salmon (Scotland 1930) Hatchery and wild salmonids Global maybe except Australia, NZ ?

Clinical signs Systemic infection slowly progressive Acute and chronic forms External: exophthalmia, blood filled blisters on skin, pale gills, etc. Internal: multifocal grey-white nodules on kidney and other organs, cloudy fluid in body Cavity, cystic cavities in skeletal muscle, etc.

Diagnosis Gram Positive Fish Pathogen 0.5 X 1 µm pairs or short chains Requires L-cystein Serum or blood enhances growth Slow growing - 20 - 60 d Survives inside phagocytic cells FAT/ELISA Clinical signs/exam

Control/treatment Erythromycin (injection of adults) Reduce loads and transmission In feed Expensive and not approved for food fish No vaccines available Avoid infection

Disease of unknown etiology Strawberry disease Symptoms Reddened raised inflammation on skin Morbidity 10-15% Market size fish affected Cause Bacterial (?) Allergic reaction (?) Treatment Antibiotics (withdrawal period)