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International Society for Infectious Diseases <http://www.isid.org>

Date: Fri 14 Sep 2012
Source: WKTV [edited]

A portion of the fish being reared at the Rome State Fish Hatchery have been suffering from a severe outbreak of furunculosis, a bacterial fish disease, for the past several months, the state Department of Environmental Conservation (DEC) announced today [14 Sep 2012]. In an effort to eliminate the disease from the hatchery, 131 000 brown trout and brook trout were destroyed earlier this week.

"DEC does not stock sick fish into the wild, and, unfortunately, this was the only way to address this disease outbreak at the Rome Fish Hatchery," said DEC Commissioner Joe Martens. "Our Fish Culture staff takes great pride in the fish that they produce, and this was not an easy decision for us to make. The DEC fish hatchery system produces
2.4 million catchable size brook, brown, and rainbow trout for spring stocking each year, and lethal measures are only considered after all other attempts at disease control are exhausted."

Fish health concerns at the hatchery began in November 2011, when large numbers of brown trout fry succumbed to a number of diseases.
The loss left DEC facing a shortage of brown trout that would be stocked in the spring of 2013 as catchable-size yearlings. Neighboring states were contacted to see whether surplus fish were available to help alleviate DEC's shortage, and 175 000 fingerling brown trout were imported from the state of Virginia to the Rome Hatchery in the spring of 2012. These fish had been tested before being brought into the hatchery and were determined to be disease-free.

Furunculosis was 1st diagnosed at the Rome Hatchery in late June 2012, when samples from the Virginia brown trout tested positive. Within a month, the furunculosis infection was severe and had spread to Adirondack and mixed-strain brook trout, both known to be susceptible to this disease. It is not known whether the disease came in with the Virginia fish or had some other origin. The disease, combined with a number of secondary infections, led to high mortality despite repeated therapeutic treatments. Most of the Virginia brown trout did not survive, and by early September 2012, only 47 000 remained.

Heavy mortality was also seen in brook trout, which numbered 84 000 by early September 2012. These brook trout were intended for stocking this fall [2012] in the Adirondacks, constituting almost 25 percent of DEC normal stocking into Adirondack lakes and ponds.

In early September [2012], hatchery personnel removed heavily infected lots of fish from the Rome Hatchery. Brook trout intended for fall stocking would not be able to be stocked in accordance with sound management practice and DEC regulations. Given their disease status and the long-term best interest of the state's hatchery program, it was decided to eradicate the disease from the hatchery as soon as possible. Targeted lots included the Adirondack and mixed-strain brook trout and the Virginia brown trout, roughly 131 000 fish in total. The fish were humanely destroyed using carbon dioxide on 10-11 Sep [2012].

A hatchery mitigation plan has been drafted outlining measures to be taken to clean up the hatchery, including restrictions on transfers of fish in and out of Rome Hatchery, biosecurity measures, and a testing plan to determine whether and when remaining lots are free of infection.

Due to pre-existing shortages and the furunculosis outbreak, it is expected that 224 lakes and ponds in the Adirondacks will be stocked with brook trout, 102 fewer than originally planned. Many of the ponds not stocked will still have holdover fish from previous years'
stockings and continue to provide excellent angling. There will also be fewer brown trout yearlings to stock in the spring of 2013 than usual, but final inventories will not be conducted until early next year [2013].

Communicated by:
ProMED-mail from HealthMap alerts

[Furunculosis is a serious septicemic bacterial disease that occurs principally in salmonid fishes. The disease is caused by a Gram-negative bacterium, _Aeromonas salmonicida_.

The disease may be an acute or chronic condition with a variety of clinical signs. It generally appears to develop as a septicaemia and is often fatal. Affected fish often show darkening of skin, lethargy and inappetence. Haemorrhages may occur at the bases of fins and the abdominal wall, heart and liver. Enlargement of the spleen and inflammation of the lower intestine are common features of chronic infections, but in acute outbreaks, fish may die rapidly with few signs. The disease is named after the raised liquefactive muscle lesions (furuncles) which sometimes occur in chronically infected fish.

The major route of transmission appears to be via infected fish and contaminated water. Although the disease causes mortality of all ages, the most serious losses occur during spring and autumn in sea water farms. An important aspect of furunculosis is the carrier state, which is often established after the fish have been exposed to _A.
salmonicida_. Clinical outbreaks and mortality appear to be triggered by stress factors such as crowding, poor water quality, fright, high temperature and physical trauma.

A map of the affected area can be accessed at <http://healthmap.org/r/3qOD>. - Mod.PMB]

[see also:
Furunculosis, cutthroat trout - USA (Nevada) 20000313.0347] .................................................sb/pmb/msp/mpp/ll
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