Craydaddy
07-27-2005, 01:57 PM
Just got this from the PA Fish and Boat Commission. Interesting read!
pfbc PROBING INFECTION IMPACTING YOUNG SMALLMOUTH BASS IN SUSQUEHANNA WATERSHED
The Pennsylvania Fish and Boat Commission (PFBC) today said that it has identified the common bacterial agent causing skin anomalies in young smallmouth bass at various locations throughout the Susquehanna River watershed and is working to learn more about its impacts.
PFBC biologists making their annual collections of young-of-year smallmouth bass over the past several weeks have observed an unusually high number of the fish with skin lesions. At the same time, recreational anglers have been making reports of seeing dead and dying young smallmouth in a variety of locations throughout the river system.
Examinations of afflicted fish have revealed that an infectious bacterial agent is responsible for the skin condition and for the mortalities. The bacterial agent, Flavobacterium columnare (columnaris), is a common soil and water bacteria. While harmless to humans, columnaris can infect all species of freshwater fish. Columnaris disease is a secondary infection brought on by environmental or nutritional factors that stress fish.
Fish health can be caused by a combination of environmental and other factors that do not individually cause significant problems, but collectively are sufficiently stressful to cause disease. Although a pollutant has not been ruled out in the current fish loss, a discrete pollutant doesn’t usually cause mortality or stress over an area as large as the affected section of the Juniata and Susquehanna Rivers.
The specific stress factors associated with the current smallmouth bass infections are hard to pinpoint, but most likely include high water temperatures and low dissolved oxygen levels. Columnaris mortalities are known to occur when water temperatures exceed 65 degrees; Susquehanna River temperatures have exceeded 80 degrees during the ongoing annual field sampling. Likewise, Commission biologists have recorded low dissolved oxygen readings from the waters they have sampled. Recently on the Juniata River, dissolved oxygen was measured at 4.65 milligrams per liter at 9 a.m. Overnight dissolved oxygen levels can be expected to dip below daytime levels; anything below 4.0 mg/l can be stressful to fish.
Smallmouth bass young-of-year inhabit shallow, near shore areas, where water temperature can be expected to be highest and dissolved oxygen levels lowest. While some adult smallmouth bass and adult white suckers have been reported to exhibit the anomaly being seen in the young bass, those occurrences have been very low.
Although water pollution has not been completely ruled out in the current fish loss, pollutants rarely impact just one species of fish. Likewise, a single pollution event doesn’t usually cause mortality or stress over an area as large as is being documented. Reports from biologists and anglers indicate the fish disease is being seen primarily in the Juniata River downstream of Lewistown and the Susquehanna River downstream from Sunbury to below Harrisburg. Lighter incidences have been reported from the West Branch Susquehanna River, the North Branch Susquehanna River, Loyalsock Creek, and Penns Creek. To date, the fish flesh anomaly has not been reported from the other major rivers of Pennsylvania such as the Delaware, Lehigh, Schuylkill, Allegheny, and Ohio.
Tissue samples from Juniata River smallmouth bass are also being tested for other fish pathogens by U.S. Fish and Wildlife Service staff at the National Fish Health Laboratory in Lamar.
The long-term impact of this outbreak on bass populations in the affected areas is also a bit of an unknown. PFBC biologists have annually made collections of young-of-year smallmouth bass since the late 1980s. The purpose of the measurements is to index the density of the bass year-class produced which provides insight to the density of adult smallmouth bass several years into the future. It takes about 3 to 4 years for young smallmouth bass to reach the legal size of 12 inches, so the index helps biologists predict the density of adults 3 or 4 years into the future. Since 2000, production of young smallmouth bass in the Susquehanna drainage has been below average due to high spring flows and cool temperatures. The impacts of those weak year classes are now being seen in somewhat lower catch rates by recreational anglers.
In 2005, preliminary results suggest young of year smallmouth bass density will be better throughout most of the Susquehanna system. The persistence of columnaris infections, however, may change that estimate. For example 46% of the smallmouth bass examined from a Juniata River sample show the presence of columnaris bacteria. The ultimate strength of the 2005 year-class will likely be determined by the persistence of high temperatures, low dissolved oxygen levels, and other factors that collectively are sufficiently stressful to cause disease and mortality.
pfbc PROBING INFECTION IMPACTING YOUNG SMALLMOUTH BASS IN SUSQUEHANNA WATERSHED
The Pennsylvania Fish and Boat Commission (PFBC) today said that it has identified the common bacterial agent causing skin anomalies in young smallmouth bass at various locations throughout the Susquehanna River watershed and is working to learn more about its impacts.
PFBC biologists making their annual collections of young-of-year smallmouth bass over the past several weeks have observed an unusually high number of the fish with skin lesions. At the same time, recreational anglers have been making reports of seeing dead and dying young smallmouth in a variety of locations throughout the river system.
Examinations of afflicted fish have revealed that an infectious bacterial agent is responsible for the skin condition and for the mortalities. The bacterial agent, Flavobacterium columnare (columnaris), is a common soil and water bacteria. While harmless to humans, columnaris can infect all species of freshwater fish. Columnaris disease is a secondary infection brought on by environmental or nutritional factors that stress fish.
Fish health can be caused by a combination of environmental and other factors that do not individually cause significant problems, but collectively are sufficiently stressful to cause disease. Although a pollutant has not been ruled out in the current fish loss, a discrete pollutant doesn’t usually cause mortality or stress over an area as large as the affected section of the Juniata and Susquehanna Rivers.
The specific stress factors associated with the current smallmouth bass infections are hard to pinpoint, but most likely include high water temperatures and low dissolved oxygen levels. Columnaris mortalities are known to occur when water temperatures exceed 65 degrees; Susquehanna River temperatures have exceeded 80 degrees during the ongoing annual field sampling. Likewise, Commission biologists have recorded low dissolved oxygen readings from the waters they have sampled. Recently on the Juniata River, dissolved oxygen was measured at 4.65 milligrams per liter at 9 a.m. Overnight dissolved oxygen levels can be expected to dip below daytime levels; anything below 4.0 mg/l can be stressful to fish.
Smallmouth bass young-of-year inhabit shallow, near shore areas, where water temperature can be expected to be highest and dissolved oxygen levels lowest. While some adult smallmouth bass and adult white suckers have been reported to exhibit the anomaly being seen in the young bass, those occurrences have been very low.
Although water pollution has not been completely ruled out in the current fish loss, pollutants rarely impact just one species of fish. Likewise, a single pollution event doesn’t usually cause mortality or stress over an area as large as is being documented. Reports from biologists and anglers indicate the fish disease is being seen primarily in the Juniata River downstream of Lewistown and the Susquehanna River downstream from Sunbury to below Harrisburg. Lighter incidences have been reported from the West Branch Susquehanna River, the North Branch Susquehanna River, Loyalsock Creek, and Penns Creek. To date, the fish flesh anomaly has not been reported from the other major rivers of Pennsylvania such as the Delaware, Lehigh, Schuylkill, Allegheny, and Ohio.
Tissue samples from Juniata River smallmouth bass are also being tested for other fish pathogens by U.S. Fish and Wildlife Service staff at the National Fish Health Laboratory in Lamar.
The long-term impact of this outbreak on bass populations in the affected areas is also a bit of an unknown. PFBC biologists have annually made collections of young-of-year smallmouth bass since the late 1980s. The purpose of the measurements is to index the density of the bass year-class produced which provides insight to the density of adult smallmouth bass several years into the future. It takes about 3 to 4 years for young smallmouth bass to reach the legal size of 12 inches, so the index helps biologists predict the density of adults 3 or 4 years into the future. Since 2000, production of young smallmouth bass in the Susquehanna drainage has been below average due to high spring flows and cool temperatures. The impacts of those weak year classes are now being seen in somewhat lower catch rates by recreational anglers.
In 2005, preliminary results suggest young of year smallmouth bass density will be better throughout most of the Susquehanna system. The persistence of columnaris infections, however, may change that estimate. For example 46% of the smallmouth bass examined from a Juniata River sample show the presence of columnaris bacteria. The ultimate strength of the 2005 year-class will likely be determined by the persistence of high temperatures, low dissolved oxygen levels, and other factors that collectively are sufficiently stressful to cause disease and mortality.