The Influence of Water Chemistry and Gill Physiology on the Uptake of the Lampricide TFM by Lake Sturgeon (Acipenser fulvescens)

Application of 3-trifluoromethyl-4-nitrophenol (TFM) to control invasive sea lamprey (Petromyzon marinus) within the Laurentian Great Lakes seldom causes non-target mortality. However, under certain conditions, TFM can harm species such as the lake sturgeon (Acipenser fulvescens). Lake sturgeon less than 100mm in length are particularly vulnerable to TFM-induced mortality, and are more sensitive to TFM toxicity with increasing water alkalinity as compared to sea lamprey. The objectives of this study were to evaluate the influence of pH and alkalinity on the uptake of TFM by juvenile sturgeon using radio-labeled TFM (14C-TFM). An additional objective was to resolve why younger (YOY; young of the year) lake sturgeon were more vulnerable to TFM than older (1+; 1 year or older) animals under the same conditions. Inverse relationships were observed between the rates of TFM uptake with water pH. These pH effects support the hypothesis that greater TFM toxicity at low pH is likely a direct result of increasing concentrations of the un-ionized, more lipophilic form of TFM at lower pH, leading to greater rates of uptake via passive diffusion across the gills. Uptake of TFM was also reduced as water alkalinity increased from low (50 CaCO3 L-1) to moderate alkalinity (150 mg CaCO3 L-1), but further reductions in TFM uptake were negligible at higher alkalinities. The reductions in TFM uptake between low and moderate alkalinity were likely due to a higher capacity of the water to buffer acidic equivalents (H+ and CO2) excreted across the gill, resulting in less acidification of the gill microenvironment and therefore the formation of less un-ionized TFM. Measurements of Na+/K+-ATPase and V-ATPase activity, as well as western blotting and immunohistochemical staining, demonstrated that TFM had no adverse effects on the ionoregulatory machinery of the gills. Regardless of water chemistry conditions, the rates of TFM uptake were greatest in the YOY sturgeon than in the 1+ fish, likely due to the higher mass specific metabolic rates of the smaller fish. In conclusion, the inverse relationship between body size and TFM uptake contributes to the greater sensitivity of YOY sturgeon to TFM. Alkalinity is also protective against TFM toxicity, but the protective effects of alkalinity are negligible in waters of high alkalinity. To minimize the risk of non-target mortality in lake sturgeon, it would be prudent to conduct treatments in the fall when sturgeon are larger and have lower rates of TFM uptake. Water chemistry also has pronounced effects on TFM uptake by lake sturgeon, and should be considered prior to TFM applications to protect them from the adverse of effects of TFM, without compromising sea lamprey control efforts