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The Problem
Various strategies have been developed or proposed to aid in reversing the declines of migratory salmonid populations in the Columbia and Snake River basins. However, important questions remain concerning the relative importance of various sources of mortality of these salmonids, and the most effective means of reversing the population declines. During the course of their migration to the sea, juvenile salmonids traveling from the Snake River must pass through as many as 8 dams. Knowledge of the cumulative effects of passage through single or multiple dams is important in assessing the relative effectiveness of in-river migration of fish versus downriver transportation by truck or barge. In addition, this element is important in terms of various water management scenarios such as increased spill of water over the dams or draw-down of water behind the dams. The cumulative response to repeated stressors experienced by juvenile salmonids during collection and transportation or in-river migration may temporarily suppress functions of the immune system. Activation of chronic diseases by stress, or increased susceptibility to new pathogens encountered in the river, estuary, or marine environments, could be a major cause of mortality for juvenile salmonids during early marine life. A pathogen of particular interest is Renibacterium salmoninarum, the causative agent of bacterial kidney disease (BKD). Renibacterium salmoninarum is considered to be the most important salmonid bacterial pathogen in the Columbia and Snake River basins, and is especially prevalent in juvenile spring and summer chinook salmon, Oncorhynchus tshawytscha. Evidence exists that migratory salmonids that become infected with the pathogen in fresh water may die of BKD during downstream migration or after entry into seawater. Nearly all information concerning the impact of the transportation process on the physiology, performance, and health of migrating salmonid smolts has been collected from studies with hatchery fish, but wild fish are the individuals of interest under the Endangered Species Act. If decisions are to be made to benefit wild fish, it is imperative to know how wild fish respond to handling and transportation. Objectives
This research subtask has two principal objectives: (1) to determine the effects of various aspects of the juvenile fish collection, bypass, and transportation operations on the health of juvenile salmonids; and (2) to determine if significant differences exist between wild and hatchery salmonids such that they might have different survivorship following collection, bypass, or transportation. The research at the WFRC is primarily focused on investigating the impact of procedures for collection, bypass or transportation on the resistance of juvenile chinook salmon to BKD. Methodology Techniques developed at the WFRC are being used for the detection of R. salmoninarum in fish and water samples taken at hydroelectric dams. These include the enzyme-linked immunosorbent assay (ELISA), polymerase chain reaction (PCR), and the membrane filtration-fluorescent antibody test (MF-FAT). Waterborne challenges of R. salmoninarum are being used in laboratory studies to mimic natural challenges. Highlights and Key Findings Studies showed no difference between wild and hatchery fish in the prevalence of two pathogens, R. salmoninarum and the parasite Nucleospora salmonis, for chinook salmon and steelhead (Oncorhynchus mykiss) smolts collected at various points in the fish transportation and bypass systems of the Columbia and Snake rivers. These results supported the findings of earlier WFRC work, which found that R. salmoninarum was present in wild juvenile spring chinook salmon residing in streams remote from hatchery influence.
Our research determined that bacteria, including R. salmoninarum, become concentrated in recirculating water systems used for fish sorting and marking at hydroelectric dams. To reduce bacterial numbers in these systems, ultraviolet (UV) sterilization systems have been installed in some recirculating systems. The sterilization efficacy of the UV sterilization unit installed in a state juvenile fish facility at Lower Granite Dam on the Snake River was studied. Results showed that the UV unit was not effective for reducing the total number of viable bacteria in the water system. In fact, bacterial numbers in the sorting and marking troughs usually showed significant increases from the first to last samples, and were positively correlated with the number of fish handled in the system. Factors such as the presence of particulate matter in the water, or water flow patterns that allowed buildup of bacteria in parts of the system, might have decreased the effectiveness of UV sterilization. Further research has been studying a modified UV system in a federal juvenile fish facility at Lower Granite Dam. In contrast to the state facility, in which water from the sorting and marking troughs circulates through the same UV system, separate UV units are used for sterilization of the recirculating water from the sorting and marking troughs in the federal facility. In addition, water from each recirculating system in the federal facility passes through 100 micron and 25 micron filters before entering the UV units, whereas water from the recirculating system in the state facility passes through a single 60 micron filter before UV sterilization. Preliminary results indicated that this UV system was more effective than the system in the state facility for reducing numbers of total viable bacteria. Analyses of R. salmoninarum concentrations in the system are ongoing. Where Are We Headed In 2003
Research has shown that R. salmoninarum becomes concentrated in the sorting and marking systems of juvenile fish facilities at hydroelectric dams. However, the membrane filtration-fluorescent antibody test (MF-FAT), the principal method used for detection of the bacterium in water, cannot distinguish live from dead organisms. In culture, the fastidious R. salmoninarum is often overgrown by faster-growing organisms, even when a selective medium is used. Studies in FY 2003 will concentrate on improvements to detection methods to enable determination of cell viability and the use of larger-volume water samples. Methods to be investigated include incorporation of a live/dead stain in the MF-FAT, use of solid-phase laser cytometry, use of a quantitative polymerase chain reaction for viable cells, and use of modified large-volume selective culture techniques. Project Contact Diane Elliott Email: diane_elliott@usgs.gov Publications |
