Salmon Mortality Increases When Pesticide and Virus Act Together

Salmon Mortality Increases When Pesticide and Virus Act Together - US - Salmon populations are already dwindling because of pesticides and disease. A new study demonstrates the synergistic effects of these two stressors - specifically esfenvalerate (Es) and infectious hematopoietic necrosis virus (IHNV) - as leading to increased mortality in juvenile Chinook salmon.

The study is published in the latest issue of Environmental Toxicology and Chemistry. At a glance, the decline of the salmon population can be attributed to such factors as overfishing, pollution, construction and operation of dams, loss of marshlands and estuaries, and river-water allocation for cities and farms. Additionally, the studied virus, IHNV, causes significant losses of juveniles in hatcheries and trout farms and is the most important viral pathogen found among Pacific salmon in the western United States.

To test their hypothesis, the studys researchers performed three trials, exposing juvenile Chinook salmon to sublethal levels of the widely used pesticides Es and chlorpyrifos (Cp) either alone or concurrently with IHNV. Among groups exposed to both Es and IHNV, 83% experienced highly significant mortality, ranging from 20 to 90% at three days post-virus exposure. Cumulatively, these fish died 2.4 to 7.7 days sooner than fish exposed to IHNV alone. This trend was not seen in any other treatment group.

The combined effects of the virus and Es are a red flag, especially considering the Es concentration used should not have been lethal. The results of the study, the researchers said, show the need to rethink acceptable concentrations of pollutants that are acting as a synergy with other environmental stressors.

To read the entire study, click here:
http://www.allenpress.com/pdf/entc_24_721_1766_1772.pdf (PDF)

Source: Alliance Communications Group - 27th June 2005