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

Date: Tue 20 Sep 2011
Source: Reuters [edited]

Wildlife officials have discovered thousands of dead fish along the Arkansas River in Little Rock and were still counting carcasses on Tuesday [20 Sep 2011], a day after an angler reported seeing dozens of dead white bass.

"We are on the river trying to determine the extent of the fish kill,"
said Keith Stephens, public information coordinator for the Arkansas Game and Fish Commission.

Wildlife investigators said the dead fish were mainly white bass, which are common in the river, and were between 5 and 8 inches [13-20 cm] long. Most were found near the foot of the Two Rivers Bridge, an 80-foot [25 m] pedestrian bridge that opened in July [2011].

An Arkansas Department of Pollution Control and Ecology official said toxins had not been eliminated as a potential cause and that oxygen levels had tested normal so far. Other test results for disease and parasites could take a month to conclude.

In late December [2010], thousands of freshwater drum and yellow bass died in the Arkansas River. A month later, 500 more drum died.
Officials later determined that the fish kills were likely caused by increases in atmospheric oxygen and nitrogen in the water after spillway gates were opened.

The massive winter fish kill had appeared especially alarming because it occurred around the same time thousands of red-winged blackbirds dropped dead from the sky on New Year's Eve [31 Dec 2010] near Beebe, Arkansas. Studies later concluded that the birds died from blunt force trauma possibly caused by unusually loud noises.

Fish kills are not uncommon, according to the game and fish officials, and are often caused by reduced oxygen in the water, algae bloom, or overpopulation. Infectious disease, parasites, and toxicity can also cause fish kills.

Stephens said that because Monday's [19 Sep 2011] discovery was in a different location from the fish kills last winter, the white bass deaths were unlikely to be caused by gas bubble trauma.

Seasonal changes in water temperature can also cause such deaths, officials said.

[Byline: Suzi Parker]

Communicated by:
ProMED-mail from HealthMap alerts

[Arkansas can be located on the HealthMap/ProMED-mail interactive map at <http://healthmap.org/r/1gZo>. - Sr.Tech.Ed.MJ]

[Although the article indicates the investigators do not expect this to be gas bubble trauma (GBT), there are indications below that may lead us to believe otherwise.

This article does not give a good indication of time. How long did it take this number of fish to succumb? This may be a very acute event or one that has been slowly festering and growing until noticed.

However, considering these fish are only 5-8 inches (13-20 cm) long, GBT is a plausible explanation. A necropsy and appropriate testing on these fish will rule out other possible causes.

The article mentions toxins, but toxins would be more likely to affect all fish, not just a certain type or size. I cannot think of any disease that would be specific to white bass. So clearly we will be awaiting the report of this situation.

However, in the mean time, information of GBT is provided below for information.

Dissolved gas supersaturation (DGS) and gas bubble trauma (GBT) in fish is a physical cause-biological effect relationship, which has received the attention of environmental scientists for the past several decades.

Dissolved gas super-saturation can produce a variety of physiological signs which are harmful or fatal to fish and other aquatic and marine organisms (Renfro 1963, Stroud and Nebeker 1976, Weitkamp and Katz 1980, Cornacchia and Colt 1984, Johnson and Katavic 1984, Gray et al.
1985, Fidler 1988, White et al. 1991). As a class, these signs are referred to as gas bubble trauma (Fidler 1984) or gas bubble disease (Bouck 1980). The major signs of GBT, which can cause death or high levels of stress in fish are:
- Bubble formation in the cardiovascular system, causing blockage of blood flow and death (Jensen 1980, Weitkamp and Katz 1980, Fidler 1988).
- Overinflation and possible rupture of the swim bladder in young (or
small) fish, leading to death or problems of overbuoyancy (Shirahata 1966, Jensen 1980, Fidler 1988, Shrimpton et al. 1990 a and b).
- Extracorporeal bubble formation in gill lamella of large fish or in the buccal cavity of small fish, leading to blockage of respiratory water flow and death by asphyxiation (Fidler 1988, Jensen 1988).
- Sub-dermal emphysema on body surfaces, including the lining of the mouth. Blistering of the skin of the mouth may also contribute to the blockage of respiratory water flow and death by asphyxiation (Fidler 1988, White et al. 1991).

Other signs of GBT include exophthalmia and ocular lesions (Blahm et al. 1975, Bouck 1980, Speare 1990), bubbles in the intestinal tract (Cornacchia and Colt 1984), loss of swimming ability (Schiewe 1974), altered blood chemistry (Newcomb 1976), and reduced growth (Jensen 1988, Krise et al. 1990), all of which may compromise the survival of fish exposed to DGS over extended periods.

Portions of this comment have been extracted from <http://www.env.gov.bc.ca/wat/wq/BCguidelines/tgp/tgptextonly.htm>. - Mod.TG]

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