Great Lakes Fishery Commission

Higher water temperatures in the summer increase the tolerance of larval sea lamprey to the lampricide 3-trifluoromethyl-4-nitrophenol (TFM). To minimize the risk of residual sea lamprey at warmer temperatures, higher concentrations of TFM may therefore be required for treatments in summer than in spring or fall. However, using higher concentrations of TFM in the summer could negatively impact non-target fishes. Concerns about warmer temperatures are not restricted to treatments with TFM alone. Depending on morphology and discharge, some rivers are treated with TFM supplemented with 0.5-1.5 % niclosamide (Nic), which enhances TFM toxicity to sea lamprey and reduces TFM requirements and costs. Yet, there is little data on how the tolerance of sea lamprey or non-target fishes to TFM/niclosamide mixtures (TFM/Nic) changes with temperature. Our goal is to understand how the sensitivity and physiological responses of non-target fishes to TFM and TFM/Nic mixtures compare to those of larval sea lamprey over a range of environmentally relevant temperatures. The objectives of our project will be to: (I) Determine how the sensitivity of non-target fishes to TFM and TFM/Nic is affected by warmer temperatures compared to larval sea lamprey; (II) Characterize how exposure to environmentally relevant concentrations of TFM or TFM/Nic in warmer waters affects the physiology of non-target fishes; (III) Ascertain how temperature affects the uptake, detoxification, and elimination of lampricides by non-target fishes and sea lamprey. \\\\r\\\\nTo address these objectives, we will compare how the toxicity of TFM or TFM/1% niclosamide mixtures varies with warmer temperature amongst larval sea lamprey and non-target fishes with a range of TFM sensitivities. Non-target species to be examined include relatively TFM sensitive brown bullhead (Ameiurus nebulosus) and lake sturgeon (Acipenser fulvescens), moderately tolerant rainbow trout (Oncorhynchus mykiss), and highly TFM tolerant bluegill (Lepomis macrochirus). The relative TFM or TFM/Nic tolerance of different non-target fishes compared to lamprey will be determined by measuring the respective TFM 9-h LC50 at different temperatures (6, 12, 18, 24°C) using static toxicity tests. Physiological disturbances in non-target fishes caused by TFM or TFM/Nic will be determined by exposing them to the corresponding sea lamprey LC50 for 12 h at different temperatures (6, 12, 24°C) followed by recovery in lampricide-free water. Tissues (brain, gill, liver, muscle) will be collected at different intervals (3, 6, 9 h exposure; 24 h recovery) for measurement of known physiological and molecular markers of lampricide exposure including energy stores (glycogen, phosphocreatine), metabolites (lactate), and stress indices (blood glucose, cortisol). We will also measure the mRNA transcript abundance of key enzymes of detoxification (e.g. glucuronyl transferases, sulfotransferases, cytochrome P450s, xenobiotic transporters) and stress proteins (HSPs) using RT-qPCR, with primers designed using existing reference transcriptomes. The relationship between temperature and lampricide uptake by non-target fishes and sea lamprey will be examined using radio-labelled lampricides (14C-TFM; 14C-Nic). Effects of temperature on lampricide accumulation, detoxification and elimination will be assessed by measuring parent lampricides and detoxification products in liver and muscle, collected over 12 h of sub-lethal lampricide exposure, using established LC-MS/MS methods. \\\\r\\\\nUnder the lampricide theme, this work will answer two key questions. First, are similar temperature-dependent increases in TFM tolerance observed when sea lamprey are exposed to TFM/Nic mixtures? Second, do non-target fishes experience similar temperature dependent increases in lampricide tolerance as those observed in sea lamprey? By answering these questions, this project will provide information on the need to develop or modify lampricide application procedures to minimize residual sea lamprey and non-target effects in warmer waters. \\\\r\\\\n

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