**The title, authors, and abstract for this completion report are provided below. For a copy of the completion report, please contact the GLFC via e-mail or via telephone at 734-662-3209**
Modes of lampricide toxicity on larval lampreys and non-target fishes
Michael P. Wilkie1, Yuziang S. Wang2, and Grant B. McClelland3
1 Department of Biology, Wilfrid Laurier University, Waterloo, Ontario, N2L 3C5
2 Department of Biology, Queen’s University, Kingston Ontario, K7L 3N6
3 Department of Biology, McMaster University, Hamilton, Ontario, L8S 4K1
The lampricide, 3-trifluoromethyl-4-nitrophenol (TFM), has been used in the integrated pest management of the sea lamprey for almost sixty years. This lampricide selectively targets larval sea lampreys in their nursery streams, is short-lived and usually has minimal impact on non-target fishes. Despite its success in controlling sea lamprey populations, significant gaps exist in our understanding of the mechanism(s) of toxicity of TFM in lamprey and nontarget fishes. The overarching aim of this research was to identify the mechanism of toxicity of TFM. The two main objectives of this research were to (i) Determine if the toxic effects of TFM result from impaired ATP synthesis due to an uncoupling of oxidative phosphorylation in the mitochondria, and (ii) establish if TFM interfered with gill mediated ion uptake leading to internal electrolyte imbalances that caused death. To test the hypothesis that TFM uncoupled oxidative phosphorylation, oxygen consumption rates were measured in isolated mitochondria collected from upstream-migrant lamprey or non-target rainbow trout (Oncorhynchus mykiss), in the presence or absence of TFM. As predicted, TFM interfered with oxidative ATP production by mitochondria in a similar manner to a known uncoupler of oxidative phosphorylation, 2,4-dinitrophenol. Measurements of mitochondrial transmembrane electrical potential (TMP) indicated that that TFM directly targeted the permeability of the inner mitochondrial membrane leading to a break-down in the electrochemical proton gradients that drive ATP synthesis. A consequence of this impairment of aerobic ATP production was a mismatch between ATP supply and ATP demand forcing larval, parasitic and upstream migrant lampreys, and rainbow trout to rely on anaerobic energy pathways to meet their energy requirements during exposure to toxic concentrations of TFM (12-h LC50 or LC99.9). These TFM-induced increases in anaerobic metabolism lead to marked reductions in brain and muscle phosphocreatine (PCr) concentrations, which helped sustain ATP production when ATP supply was reduced. Pronounced reductions in brain, liver and kidney glycogen were also observed as a result of increased dependence upon anaerobic glycolysis in both lamprey and trout. Death likely ensued when the ATP supplied via anaerobic glycolysis and PCr hydrolysis was insufficient to meet the energetic demands of the central nervous system. Although TFM is known to cause damage to the gills of lamprey, its effects on rates of gill mediated Na+ uptake and internal ion (Na+, Cl-, and Ca2+) balance were absent or relatively minor. We conclude that the mode of action of TFM occurs through an uncoupling of oxidative phosphorylation occurring in the mitochondria, leading to reductions in oxidative ATP supply that compromise the ability of lamprey and trout to meet their energetic demands. Because glycogen stores are essential for ensuring that adequate ATP is generated during periods of reduced ATP supply or increased ATP demand, the TFM sensitivity of lampreys and nontarget fishes might be related the size of the body’s glycogen pool. Thus, factors that influence the size of the glycogen pool of lampreys and non-target fishes including season, dietary status, life stage and the presence of environmental stressors, could be critical determinants of TFM sensitivity.