The Influence of Abiotic Factors on the Uptake and Elimination of 3-Trifluoromethyl-4-Nitrophenol by Larval Sea Lamprey (Petromyzon marinus)

The backbone of sea lamprey (Petromyzon marinus) control in the Great Lakes is the use of the piscicide, 3-trifluoromethyl-4-nitrophenol (TFM), which is applied to streams containing larval sea lampreys. However, TFM effectiveness can be influenced by abiotic factors such as pH and temperature, which fluctuate daily and seasonally. The objectives of this thesis were to evaluate the influence of pH, temperature, and season on the toxicity, uptake, and elimination of TFM by larval sea lamprey. Radio-labeled TFM (14C-TFM) was used to determine how TFM uptake rates varied at different water pHs or temperatures during exposure to TFM at the 12 h LC50 (4.6 mg L-1) or 12 h LC99(7.6 mg L-1)of larval lamprey. These experiments indicated that TFM uptake rates were 4-5.5 fold greater at pH 6.5 compared to pH 9.0 and whole body TFM accumulation was also greater at pH 6.5. These differences were likely because a greater proportion of the total TFM (sum of ionized plus un-ionized TFM) concentration was in its more lipophilic, un-ionized (phenolic) form at pH 6.5 compared to pH 9.0. Uptake was also greater at 22 °C compared to 6 °C, which was likely caused by increased gill ventilation due to greater metabolic rates at warm temperatures. The effects of pH and temperature on TFM excretion were then tested by injecting lamprey with 100 nmol g-1 14C-TFM and measuring its appearance in TFM-free water over 24 h. In contrast to uptake, elimination rates were 1.3-1.9 fold greater at pH 9.0 than at pH 6.5 during 2-4 h of depuration in TFM-free water. Yet, temperature had no effect on the elimination rates. Season affected the sensitivity of lamprey to TFM, where the 12 h LC50 for lamprey was 2.5 fold greater in summer than in spring. Yet, season did not influence whole body TFM concentrations in lamprey that experienced mortality during TFM exposure, averaging between 40-50 nmol g-1 wet weight. However, the internal TFM burden was approximately 2.5 fold greater in these fish compared to those that survived. Differences in TFM detoxification capacity may have explained these findings, but whole body concentrations of the metabolite, TFM-glucuronide, were below detection. Neither was mRNA abundance of the enzyme UDP-glucuronosyltransferase (UGT) influenced by season or temperature. TFM applications during spring and fall could increase TFM efficiency when larval sea lampreys are less tolerant to TFM. Applying TFM to large streams in spring or fall should also be considered because it would result in reduced concentrations of TFM needed to control larval sea lamprey populations, resulting in more economical treatments, while still protecting Great Lakes fisheries from sea lamprey parasitism/predation