The Influence of Physiological and Abiotic Factors on the Sensitivity of the Sea Lamprey (Petromyzon marinus) to the Lampricide 3-trifluoromethyl-4-nitrophenol (TFM)

Invasive sea lamprey (Petromyzon marinus) in the Great Lakes are controlled using the pesticide (lampricide) 3-trifluoromethyl-4-nitrophenol (TFM), which is applied to nursery streams containing larval lamprey. The toxicity of TFM to lamprey is affected by various environmental and physiological factors, which can lead to residual lamprey that survive TFM treatment. The goal of this study was to investigate how abiotic (season and temperature) factors interacted with physiological parameters (whole body and tissue energy reserves) to influence TFM sensitivity in sea lamprey. Toxicity tests were conducted at different times of the year (spring, early and late summer, fall) and temperatures (6, 12 and 21 °C) using larval sea lamprey collected from the same stream, the Au Sable River, Michigan, USA. Toxicity tests revealed that TFM tolerance was greatest in late summer, when the 12 h LC50 and 12 h LC99.9 were 2.0 to 2.5-fold greater than in the spring and fall, when water temperatures were cooler. Toxicity tests conducted the following year on larval sea lamprey collected from the same river, but acclimated and exposed to TFM at different temperatures, revealed that 12 h LC50 and 12 h LC99.9 increased by 50 % as water temperature increased from 6 °C to 12 °C, and was 2.5-fold greater at 21 °C than at 6 °C. In addition, body composition experiments were conducted on lamprey that were not exposed to TFM to quantify changes in energy stores with season and temperature. Seasonal variation in whole body and tissue energy stores including glycogen, lipid and protein had little influence on the differences in TFM sensitivity. No differences in TFM burden or the TFM metabolite, TFM-glucuronide, were detected in the carcasses of lamprey exposed to TFM during different seasons. Nor could any differences in body condition (condition factor, hepatosomatic index) explain the differences in TFM sensitivity with season. I conclude that increased water temperature is the primary abiotic factor contributing to the larval sea lamprey’s greater ability to withstand TFM during the summer, possibly due to an increase in their capacity to detoxify TFM. These data suggest that it may be prudent to consider seasonal variations in temperature when using current models to select and treat sea lamprey-infested streams with TFM