piscirickettsiosis

Diseases of finfish

Bacterial diseases—Piscirickettsiosis

CLICK ON IMAGE TO ENLARGE piscirickettsiosis

Piscirickettsiosis in Atlantic salmon. Note granulomas in liver and pin-point haemorrhaging in pyloric caeca.

Source: S Bravo

Signs of disease

Important: animals with disease may show one or more of the signs below, but disease may still be present in the absence of any signs.

Disease signs at the farm level

increasing mortality

Disease signs at the tank and pond level

lethargy
circling
cessation of feeding
emaciation
swimming at the sides of net-pens

Clinical signs of disease in an infected animal

multiple small white spots on skin
raised skin patches progressing to shallow ulcers on flanks and head
darkening of skin
ascites (swollen abdomen from accumulated fluid)

Gross signs of disease in an infected animal

pale gills
grey, swollen spleen and kidneys
mottled to spotted liver with large pale necrotic lesions
pinpoint haemorrhages of the stomach organs and flank muscle

Disease agent

Piscirickettsiosis is caused by the bacterium Piscirickettsia salmonis, which has recently been classified within the gamma-proteobacteria, family Piscirickettsiaceae.

Host range

Fish known to be susceptible to piscirickettsiosis:
Atlantic salmon* (Salmo salar)
chinook salmon* (Oncorhynchus tshawytscha)
coho salmon* (Oncorhynchus kisutch) - most susceptible to the bacterium
pink salmon* (Oncorhynchus gorbuscha)
rainbow trout* (Oncorhynchus mykiss)
sakura salmon* (Oncorhynchus masou)

Piscirickettsiosis is only known to affect aquaculture stock and has not been recorded in fish from the wild.

* naturally susceptible (other species have been shown to be experimentally susceptible)

Presence in Asia–Pacific

EXOTIC — has not been officially reported in the Asia–Pacific region under the NACA–FAO–OIE quarterly aquatic animal disease reporting program.

Epidemiology

Outbreaks usually occur at 12°–18°C, an unusually high water temperature for salmonids.
Little is known about the ecology of this relatively recently identified agent.
This disease results in septicaemia, with bacteria infecting the entire body through the blood.

Differential diagnosis

The differential diagnostic table and the list of similar diseases appearing at the bottom of each disease page refer only to the diseases covered by this field guide. Gross signs observed might well be representative of a wider range of diseases not included here. Therefore, these diagnostic aids should not be read as a guide to a definitive diagnosis, but rather as a tool to help identify the listed diseases that most closely account for the gross signs.

Further images

Sample collection

Because of uncertainty in differentiating diseases using only gross signs, and because some aquatic animal disease agents might pose a risk to humans, you should not try to collect samples unless you have been trained. Instead, you should phone your national hotline number and report your observations. If samples have to be collected, the agency taking the call will advise you on what you need to do. Local or district fisheries/veterinary authorities could advise you on sampling.

Emergency disease hotline

For your national emergency disease hotline number, see Whom to contact if you suspect a disease.