The lampricide 3-trifluoromethyl-4-nitrophenol (TFM) uncouples mitochondrial oxidative phosphorylation in both sea lamprey (Petromyzon marinus) and TFM-tolerant rainbow trout (Oncorhynchus mykiss)

Differences in the transcriptome response in the gills of sea lamprey acutely exposed to 3-trifluoromethyl-4-nitrophenol (TFM), niclosamide or a TFM:niclosamide mixture

Sea lamprey (Petromyzon marinus) control in the Laurentian Great Lakes of North America makes use of two pesticides: 3-trifluoromethyl-4-nitrophenol (TFM) and niclosamide, which are often co-applied. Sea lamprey appear to be vulnerable to these agents resulting from a lack of detoxification responses with evidence suggesting that lampricide mixtures produce a synergistic effect. However, there is a lack of information pertaining to the physiological responses of sea lamprey to niclosamide and TFM:niclosamide mixtures. Here, we characterized the transcriptomic responses of the sea lamprey to TFM, niclosamide, and a TFM:niclosamide (1.5 %) mixture in the gill. Along with a control, larval sea lamprey were exposed to each treatment for 6 h, after which gill tissues were extracted for measuring whole-transcriptome responses using RNA sequencing. Differential gene expression patterns were summarized, which included identifying the broad roles of genes and common expression patterns among the treatments. While niclosamide treatment resulted in no differentially expressed genes, TFM- and mixture-treated fish had several differentially expressed genes that were associated with the cell cycle, DNA damage, metabolism, immune function, and detoxification. However, there was no common differential expression among treatments. For the first time, we characterized the transcriptomic response of sea lamprey to niclosamide and a TFM:niclosamide mixture and identified that these agents impact mRNA transcript abundance of genes associated with the cell cycle and cellular death, and immune function, which are likely mediated through mitochondrial dysregulation. These results may help to inform the production of more targeted and effective lampricides in sea lamprey control efforts.

Cytotoxicity of the field lampricide 3-trifluoromethyl-4-nitrophenol (TFM) in tadpole cell lines from North American frogs

The common field lampricide, 3-trifluoromethyl-4-nitrophenol (TFM), is used to treat streams and creeks infested with highly invasive and destructive sea lamprey (Petromyzon marinus) in the tributaries of the Great Lakes. Unfortunately, amphibian deaths have been reported following stream treatments with TFM. Larval amphibians (tadpoles) are more susceptible to TFM toxicity than adult amphibians. The aim of this study was to test the toxicity of TFM in eight new tadpole cell lines from the green frog (Lithobates clamitans), wood frog (Lithobates sylvaticus), and American toad (Anaxyrus americanus). A cell viability bioassay using two fluorescent dyes, Alamar Blue and CFDA-AM, was performed following 24-h and 72-h exposures to a range of TFM concentrations. In general, TFM exposure reduced Alamar Blue fluorescence more rapidly than CFDA-AM fluorescence in tadpole cells, suggesting that Alamar Blue is perhaps a better diagnostic indicator of cell health for acute TFM cytotoxicity. At present, the in vivo 96-h LC50s of TFM are only available for L. clamitans and they correlated well with the in vitro EC50 values for the green frog tadpole cell lines in this study. The eight tadpole cell lines with different relative sensitivities to TFM cytotoxicity could prove to be useful tools in assessing next-generation lampricides in high-throughput bioassays to ensure safety in frogs before their sea lamprey-targeted application in the field.

Upstream migrant sea lamprey (Petromyzon marinus) show signs of increasing oxidative stress but maintain aerobic capacity with age

Following the parasitic juvenile phase of their life cycle, sea lamprey (Petromyzon marinus) mature into a reproductive but rapidly aging and deteriorating adult, and typically die shortly after spawning in May or June. However, pre-spawning upstream migrant sea lamprey can be maintained for several months beyond their natural lifespan when held in cold water (∼4-8 °C) under laboratory conditions. We exploited this feature to investigate the interactions between senescence, oxidative stress, and metabolic function in this phylogenetically ancient fish. We investigated how life history traits and mitochondria condition, as indicated by markers of oxidative stress (catalase activity, lipid peroxidation) and aerobic capacity (citrate synthase activity), changed in adult sea lamprey from June to December after capture during their upstream spawning migration. Body mass but not liver mass declined with age, resulting in an increase in hepatosomatic index. Both effects were most pronounced in males, which also tended to have larger livers than females. Lamprey experienced greater oxidative stress with age, as reflected by increasing activity of the antioxidant enzyme catalase and increasing levels of lipid peroxidation in liver mitochondrial isolates over time. Surprisingly, the activity of citrate synthase also increased with age in both sexes. These observations implicate mitochondrial dysfunction and oxidative stress in the senescence of sea lamprey. Due to their unique evolutionary position and the technical advantage of easily delaying the onset of senescence in lampreys using cold water, these animals could represent an evolutionary unique and tractable model to investigate senescence in vertebrates.

Variation in the Transcriptome Response and Detoxification Gene Diversity Drives Pesticide Tolerance in Fishes

Pesticides are critical for invasive species management but often have negative effects on nontarget native biota. Tolerance to pesticides should have an evolutionary basis, but this is poorly understood. Invasive sea lamprey (Petromyzon marinus) populations in North America have been controlled with a pesticide lethal to them at lower concentrations than native fishes. We addressed how interspecific variation in gene expression and detoxification gene diversity confer differential pesticide sensitivity in two fish species. We exposed sea lamprey and bluegill (Lepomis macrochirus), a tolerant native species, to 3-trifluoromethyl-4-nitrophenol (TFM), a pesticide commonly used in sea lamprey control. We then used whole-transcriptome sequencing of gill and liver to characterize the cellular response in both species. Comparatively, bluegill exhibited a larger number of detoxification genes expressed and a larger number of responsive transcripts overall, which likely contributes to greater tolerance to TFM. Understanding the genetic and physiological basis for pesticide tolerance is crucial for managing invasive species.

Niclosamide Is a Much More Potent Toxicant of Mitochondrial Respiration than TFM in the Invasive Sea Lamprey (Petromyzon marinus)

Invasive sea lampreys in the Laurentian Great Lakes are controlled by applying TFM (3-trifluoromethyl-4-nitrophenol) and niclosamide to streams infested with their larvae. Both agents uncouple oxidative phosphorylation in the mitochondria, but TFM specifically targets lampreys, which have a lower capacity to detoxify the lampricide. Niclosamide lacks specificity and is more potent than TFM. However, its greater potency is poorly understood. We tested the hypothesis that niclosamide is a stronger uncoupler of mitochondrial oxidative phosphorylation than TFM by measuring oxygen consumption rates in isolated liver mitochondria exposed to physiologically relevant concentrations of TFM, niclosamide, or their mixture (100 TFM:1 niclosamide) at environmentally relevant temperatures (7, 13, and 25 °C). Niclosamide increased State 4 respiration and decreased the respiratory control ratio (RCR) at much lower concentrations than TFM. Calculations of the relative EC₅₀ values, the amount of TFM or niclosamide required to decrease the RCR by 50%, indicated that niclosamide was 40-60 times more potent than TFM. Warmer temperature did not appear to decrease the sensitivity of mitochondria to niclosamide or TFM, as observed in the intact sea lamprey exposed to TFM in warmer waters. We conclude that the extreme sensitivity of mitochondria to niclosamide contributes to its greater in vivo toxicity in the whole animal.

Reversible disruptions to energy supply and acid-base balance in larval sea lamprey exposed to the pesticide: Niclosamide (2',5-dichloro-4'-nitrosalicylanilide)

Since the 1960s, chemical control of larval sea lamprey has been achieved using the pesticides 3-trifluoromethyl-4-nitrophenol (TFM) and niclosamide (Bayluscide®). Much more potent, niclosamide is often used as an adjuvant for TFM, and on its own to treat lentic habitats, rivers with high discharge and currents, and for population surveys. Yet, little is known about its mode of action or physiological effects on sea lamprey. Like TFM, niclosamide is thought to impair mitochondrial ATP production by uncoupling oxidative phosphorylation. We therefore tested the hypothesis that niclosamide would result in metabolic perturbations and disturbances to acid-base balance in larval lamprey due to their need to balance ATP supply with ATP demands. When larval sea lamprey were exposed to the nominal 9-h niclosamide LC₅₀ (0.11 mg L^-1) over 9 h, it resulted in significant decreases in brain, phosphocreatine (35 %) and glycogen (50 %), accompanied by a 5-fold increase in lactate. In carcass, there were 25-30 % decreases in glycogen, corresponding increases in pyruvate and lactate, and a pronounced 0.5 unit decrease in intracellular pH. Calculation of the NAD⁺/NADH ratio in the carcass indicated that neither oxygen delivery nor the flux of reducing equivalents through the mitochondrial electron transport chain were impaired by niclosamide, supporting the hypothesis that niclosamide interferes with mitochondrial ATP production by uncoupling oxidative phosphorylation. Thus, greater reliance on glycogen, characterized by higher rates of glycolysis, temporarily mitigates the corresponding shortfall in ATP supply caused by niclosamide. Notably, all lamprey that survived niclosamide exposure readily restored ATP, phosphocreatine, glycogen and acid-base balance after recovery in niclosamide-free water. This resilience suggests that sea lamprey that survive or escape niclosamide treatment could compromise sea lamprey control efforts by subsequently completing their larval stage and developing into parasitic juvenile sea lamprey that could ultimately threaten Great Lake's fisheries populations.

Disturbances to energy metabolism in juvenile lake sturgeon (Acipenser fulvescens) following exposure to niclosamide

Since the 1960s, invasive sea lamprey (Petromyzon marinus) populations in the Laurentian Great Lakes have been controlled by applying two chemicals, 3-trifluoromethyl-4-nitrophenol (TFM) and 2',5-dichloro-4'-nitrosalicylanilide (niclosamide, aka. Bayluscide®), to streams infested with larval sea lamprey. These "lampricide" applications primarily rely on TFM, and are often combined with 1-2% niclosamide, which increases treatment effectiveness. Niclosamide is also used alone to treat lentic habitats and in rivers with high discharge. However, little is known about niclosamide's possible adverse physiological effects on non-target organisms. Of particular concern is the lake sturgeon (Acipenser fulvescens), which is threatened throughout the Great Lakes basin where its habitat often overlaps with larval lamprey. Because niclosamide is believed to impair ATP production by uncoupling oxidative phosphorylation, we determined how it altered metabolic processes and acid-base balance in young-of-the-year (YOY) lake sturgeon exposed to their 9-h LC₅₀ of niclosamide (0.11 mg L^-1) for 9 h. Exposure to niclosamide led to decreased brain ATP and glucose reserves, and increased lactate, with no effect on brain glycogen. In contrast, substantial (60%) reductions in glycogen were observed in liver, suggesting that hepatic glycogen reserves were mobilized to meet the brain's glucose requirements when ATP supply was impaired during niclosamide exposure. Disturbances in carcass included reduced phosphocreatine (65-70%), 2- and 4-fold increases in pyruvate and lactate, and a slight metabolic acidosis, characterized by a 0.1 unit decrease in intracellular pH (pHi). Each of these disturbances were corrected within 24 h following depuration in clean (niclosamide-free) water. We conclude that if lake sturgeon survive exposure to niclosamide, they are able to rapidly replenish their energy stores (glycogen, ATP, phosphocreatine) and correct any corresponding metabolic disturbances within 24 h.

The lampricide 3-trifluoromethyl-4-nitrophenol causes temporary metabolic disturbances in juvenile lake sturgeon (Acipenser fulvescens): implications for sea lamprey control and fish conservation

The pesticide 3-trifluoromethyl-4-nitrophenol (TFM) is applied to rivers and streams draining into the Laurentian Great Lakes to control populations of invasive sea lamprey (Petromyzon marinus), which are ongoing threats to fisheries during the lamprey's hematophagous, parasitic juvenile life stage. While TFM targets larval sea lamprey during treatments, threatened populations of juvenile lake sturgeon (Acipenser fulvescens), particularly young-of-the-year (<100 mm in length), may be adversely affected by TFM when their habitats overlap with larval sea lamprey. Exposure to TFM causes marked reductions in tissue glycogen and high energy phosphagens in lamprey and rainbow trout (Oncorhynchus mykiss) by interfering with oxidative ATP production in the mitochondria. To test that environmentally relevant concentrations of TFM would similarly affect juvenile lake sturgeon, we exposed them to the larval sea lamprey minimum lethal concentration (9-h LC99.9), which mimicked concentrations of a typical lampricide application and quantified energy stores and metabolites in the carcass, liver and brain. Exposure to TFM reduced brain ATP, PCr and glycogen by 50-60%, while lactate increased by 45-50% at 6 and 9 h. A rapid and sustained depletion of liver glucose and glycogen of more than 50% was also observed, whereas the respective concentrations of ATP and glycogen were reduced by 60% and 80% after 9 h, along with higher lactate and a slight metabolic acidosis (~0.1 pH unit). We conclude that exposure to environmentally relevant concentrations of TFM causes metabolic disturbances in lake sturgeon that can lead to impaired physiological performance and, in some cases, mortality. Our observations support practices such as delaying TFM treatments to late summer/fall or using alternative TFM application strategies to mitigate non-target effects in waters where lake sturgeon are present. These actions would help to conserve this historically and culturally significant species in the Great Lakes.

A Toxic Unit and Additive Index Approach to Understanding the Interactions of 2 Piscicides, 3-Trifluoromethyl-4-Nitrophenol and Niclosamide, in Rainbow Trout

The toxic unit and additive index approaches were used to understand how 2 pesticides, 3-trifluoromethyl-4-nitrophenol (TFM) and 2,5-dichloro-4-nitrosalicylanilide (niclosamide; Nic), interact in mixtures. Our first objective was to determine whether the interaction was strictly additive or greater than additive at doses comparable to those used to control invasive sea lamprey (Petromyzon marinus) in the Laurentian Great Lakes, and our second was to compare the utility of the toxic unit and additive index models for determining how TFM and Nic interacted. Typically, TFM is mixed with Nic (1-2%, w/v) to increase its potency and reduce TFM use. However, there is little information on how the 2 chemicals interact. Using a well-studied, resident nontarget fish, the rainbow trout (Oncorhynchus mykiss), we conducted toxicity tests with TFM, Nic, and TFM:Nic (100:1, w/v; TFM/1% Nic) mixtures over 12 h to determine if the interaction was strictly additive, less than additive (antagonistic), or greater than additive (synergistic). The toxic unit and additive index approaches indicated synergistic interactions at environmentally relevant concentrations, suggesting that both are valid approaches for predicting how TFM and Nic interact. The toxic unit approach was simpler to conceptualize and to calculate, and we recommend that it be used when describing how TFM and Nic, and other similar organic compounds, interact with each other in aquatic ecosystems. Environ Toxicol Chem 2021;40:1419-1430. © 2021 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Incipient resistance to an effective pesticide results from genetic adaptation and the canalization of gene expression

The resistance of pest species to chemical controls has vast ecological, economic, and societal costs. In most cases, resistance is only detected after spreading throughout an entire population. Detecting resistance in its incipient stages, by comparison, provides time to implement preventative strategies. Incipient resistance can be detected by coupling standard toxicology assays with large-scale gene expression experiments. We apply this approach to a system where an invasive parasite, sea lamprey (Petromyzon marinus), has been treated with the highly effective pesticide 3-trifluoromethyl-4-nitrophenol (TFM) for 60 years. Toxicological experiments revealed that lamprey from treated populations did not have higher survival to TFM exposure than lamprey from untreated populations, demonstrating that full-fledged resistance has not yet evolved. In contrast, we find hundreds of genes differentially expressed in response to TFM in the population with the longest history of exposure, many of which relate to TFM's primary mode of action, the uncoupling of oxidative phosphorylation, and subsequent depletion of ATP. Three genes critical to oxidative phosphorylation, ATP5PB, PLCB1, and NDUFA9, were nearly fixed for alternative alleles in comparisons of SNPs between treated and untreated populations (FST  > 5 SD from the mean). ATP5PB encodes subunit b of ATP synthase and an additional subunit, ATP5F1B, was canalized for high expression in treated populations, but remained plastic in response to TFM treatment in individuals from the untreated population. These combined genomic and transcriptomic results demonstrate that an adaptive, genetic response to TFM is likely driving incipient resistance in a damaging pest species.

Sea lamprey cardiac mitochondrial bioenergetics after exposure to TFM and its metabolites

Population control of invasive sea lamprey relies heavily on lampricide treatment of infested streams. The lampricide 3-trifluoromethyl-4-nitrophenol (TFM) is thought to impair mitochondrial ATP production through uncoupling oxidative phosphorylation. However, the effect of TFM on the entire electron transport chain (complexes I to V) in the mitochondria is not clear. In addition, TFM is reduced in phase I metabolism by sea lamprey at higher levels than in other fish species. The effects of these TFM reductive metabolites on mitochondria have not been explored. In this study, we sought to examine the effects of TFM and its reductive metabolite amino-TFM (TFMa) on cardiac mitochondrial oxygen consumption and membrane potential to delineate potential mechanisms for toxicity. To determine if molecules with similar structure also exhibit similar effects on mitochondria, we used 4-nitro-3-methylphenol (NMP) and its reductive metabolites 4-amino-3-methylphenol (NMPa) and 4-nitroso-3-methylphenol (NMPn) for comparisons. We found that mitochondrial bioenergetics was heavily affected with increasing concentrations of TFM, NMP, and NMPa when complexes I and II of the electron transport chain were examined, indicating that the toxic action of these compounds was exerted not only by uncoupling complex V, but also affecting complexes I and II.

Rapid resistance to pesticide control is predicted to evolve in an invasive fish

Xenobiotic resistance is commonly found in species with short generation times such as bacteria, annual plants, and insects. Nevertheless, the fundamental evolutionary principles that govern the spread of resistance alleles hold true for species with longer generation times. One such example could occur with sea lamprey (Petromyzon marinus), a parasitic invasive species in the Laurentian Great Lakes that decimated native fish populations prior to its control with the pesticide 3-trifluoromethyl-4-nitrophenol (TFM). Since the 1950s, tributaries have been treated annually with TFM, where treatments effectively remove most, but not all, larval sea lamprey. We developed an eco-genetic model of sea lamprey to examine factors affecting the evolution of resistance and found that resistance alleles rapidly rise to fixation after 40-80 years of treatment, despite the species' relatively long generation time (4-7 years). The absence of natal homing allows resistant individuals to spread quickly throughout the entire system, but also makes the early detection of resistance challenging. High costs of resistance and density independent reproduction can delay, but not prevent, the onset of resistance. These results illustrate that sea lamprey have the potential to evolve resistance to their primary control agent in the near future, highlighting the urgent need for alternative controls.

Control of invasive sea lampreys using the piscicides TFM and niclosamide: Toxicology, successes & future prospects

The invasion of the Laurentian Great Lakes of North America by sea lampreys (Petromyzon marinus) in the early 20th century contributed to the depletion of commercial, recreational and culturally important fish populations, devastating the economies of communities that relied on the fishery. Sea lamprey populations were subsequently controlled using an aggressive integrated pest-management program which employed barriers and traps to prevent sea lamprey from migrating to their spawning grounds and the use of the piscicides (lampricides) 3-trifluoromethyl-4-nitrophenol (TFM) and niclosamide to eliminate larval sea lampreys from their nursery streams. Although sea lampreys have not been eradicated from the Great Lakes, populations have been suppressed to less than 10% of their peak numbers in the mid-1900s. The ongoing use of lampricides provides the foundation for sea lamprey control in the Great Lakes, one of the most successful invasive species control programs in the world. Yet, significant gaps remain in our understanding of how lampricides are taken-up and handled by sea lampreys, how lampricides exert their toxic effects, and how they adversely affect non-target invertebrate and vertebrates species. In this review we examine what has been learned about the uptake, handling and elimination, and the mode of TFM and niclosamide toxicity in lampreys and in non-target animals, particularly in the last 10 years. It is now clear that the mode of TFM toxicity is the same in non-target fishes and lampreys, in which TFM interferes with oxidative phosphorylation by the mitochondria leading to decreased ATP production. Vulnerability to TFM is related to abiotic factors such as water pH and alkalinity, which we propose changes the relative amounts of the bioavailable un-ionized form of TFM in the gill microenvironment. Niclosamide, which is also a molluscicide used to control snails in areas prone to schistosomiasis infections of humans, also likely works by uncoupling oxidative phosphorylation, but less is known about other aspects of its toxicology. The effects of TFM include reductions in energy stores, particularly glycogen and high energy phosphagens. However, non-target fishes readily recover from sub-lethal TFM exposure as demonstrated by the rapid restoration of energy stores and clearance of TFM. Although both TFM and niclosamide are non-persistent in the environment and critical for sea lamprey control, increasing public and institutional concerns about pesticides in the environment makes it imperative to explore other means of sea lamprey control. Accordingly, we also address possible "next-generation" strategies of sea lamprey control including genetic tools such as RNA interference and CRISPR-Cas9 to impair critical physiological processes (e.g. reproduction, digestion, metamorphosis) in lamprey, and the use of green chemistry to develop more environmentally benign chemical methods of sea lamprey control.

The common field lampricide 3-trifluoromethyl-4-nitrophenol is a potential radiosensitizer in fish cells

PURPOSE

To evaluate if the common field lampricide 3-trifluoromethyl-4-nitrophenol (TFM) that is intended to eradicate the invasive species sea lampreys in the Great Lakes has the potential to sensitize radiation responses in cells from non-targeted native fish MATERIALS AND METHODS: The TFM toxicity was assessed acutely and chronically with the clonogenic fish cell line eelB. The acute toxicity (24-h exposure) was determined by the fluorescent cell viability probe Alamar Blue. The chronic toxicity was determined either by Alamar Blue (7-d exposure) or the clonogenic survival assay (14-d exposure). Pre- and post-exposure of fish cells to environmentally relevant TFM concentrations following gamma irradiation were performed. Clonogenic survival was determined to assess the damage level of radiation-induced reproductive cell death.

RESULTS

The chronic toxicity tests were more sensitive than the acute toxicity tests. The 14-d EC₅₀ using the clonogenic survival endpoint was 2.09 ± 0.28 μg/mL and was statistically similar to the 7-d EC₅₀ (1.85 ± 0.07 μg/mL) based on the Alamar Blue-based cytotoxicity endpoint. Post-exposure of cells to environmentally relevant TFM concentrations following irradiation did not have any effect as compared to the irradiation alone group. In contrast, pre-exposure of cells to TFM following irradiation had a negative additive effect when the total radiation dose was 2 Gy, but not 0.1 or 0.5 Gy.

CONCLUSION

Our results suggest that the common field lampricide TFM is a potential radiation sensitizer in cells from non-targeted native fish. This could be a health problem of concern for non-targeted native fish if a large accidental radioactive release occurs.

Exposure to the lampricide TFM elicits an environmental stress response in yeast

The pesticide 3-trifluoromethyl-4-nitrophenol (TFM) is used to control sea lamprey populations in the Great Lakes and Lake Champlain. Little is known about the effects of this pesticide on gene expression in eukaryotic species. This study used microarray analysis to determine the effects of short term, high dose TFM exposure on gene expression in Saccharomyces cerevisiae. Yeast grown in standard glucose-containing media showed significant variation in gene expression in pathways related to cytoplasmic translation with the majority of these genes being downregulated. These findings were supported by the analysis of a similar but glucose-free experiment revealing that these cytoplasmic translation genes, mostly ribosomal subunit expressing genes, were similarly downregulated. The repression of the ribosomal subunit genes suggests that TFM exposure, regardless of glucose availability, evokes features of the environmental stress response in yeast.

Assessing off-target cytotoxicity of the field lampricide 3-trifluoromethyl-4-nitrophenol using novel lake sturgeon cell lines

Lampricides are currently being applied to streams and rivers to control the population of sea lamprey, an invasive species, in the Great Lakes. The most commonly used lampricide agent used in the field is 3-trifluoromethyl-4-nitrophenol (TFM), which targets larval sea lamprey in lamprey-infested rivers and streams. The specificity of TFM is due to the relative inability of sea lamprey to detoxify the agent relative to non-target fishes. There is increasing concern, however, about non-target effects on fishes, particularly threatened populations of juvenile lake sturgeon (LS; Acipenser fulvescens). There is therefore a need to develop models to better define lake sturgeon's response to TFM. Here we report the establishment of five LS cell lines derived from the liver, gill, skin and intestinal tract of juvenile LS and some of their cellular characteristics. All LS cell lines grew well at 25 °C in Leibovitz's (L)- 15 medium supplemented with 10% FBS. All cell lines demonstrated high senescence-associated β-galactosidase activity and varying levels of Periodic acid Schiff-positive polysaccharides, indicating substantial production of glycoproteins and mucosubstances by the cells. Comparative toxicity of TFM in the five LS cell lines was assessed by two fluorescent cell viability dyes, Alamar Blue and CFDA-AM, in conditions with and without serum and at 24 or 72 h exposure. Deduced EC₅₀ values were compared between the cell lines and to the reported in vivo LC₅₀s. Tissues sensitive to the effects of TFM in vivo correlated with cell lines from the same tissues being most sensitive to TFM in vitro. EC₅₀ values for the LSliver-e cells was significantly lower than the EC₅₀ for the rainbow trout (RBT) liver cells RTL-W1, reaffirming the in vivo observation that LS was generally more TFM-sensitive than rainbow trout. Our data suggests that whole-fish sensitivity of LS to TFM is likely attributable to sensitivity at the cellular level. Thus, LS cell lines, as well as those of RBT, can be used to screen and evaluate the toxicity of the next generation of lampricides on non-target fish such as lake sturgeon.

Post-exposure effects of the piscicide 3-trifluoromethyl-4-nitrophenol (TFM) on the stress response and liver metabolic capacity in rainbow trout (Oncorhynchus mykiss)

The piscicide 3-trifluoromethyl-4-nitrophenol (TFM) has been used to control invasive sea lamprey (Petromyzon marinus) populations in the Great Lakes for almost 60 years. Applied to rivers and streams containing larval lampreys, TFM seldom harms non-target fishes, but the effects of sub-lethal treatments on fish physiology are not well understood. We examined the effects of 9 h exposure to TFM on the stress axis and liver metabolic capacity of rainbow trout (Oncorhynchus mykiss) using in vivo and in vitro approaches. The fish that had been acutely exposed to TFM in vivo had increased plasma cortisol levels at 12 h post-treatment, but TFM exposure did not interfere with in vitro cortisol production in head kidney preparations. Subjecting trout to an acute handling stressor 12 h post-TFM exposure resulted in a relative attenuation of the plasma cortisol and glucose response compared to pre-stress levels. We conclude that routine TFM treatments can lead to elevations of plasma cortisol following exposure, plus a relative dampening of the stress response in rainbow trout, with high cortisol levels lasting at least 12 h post-treatment. Since the ability of the fish to produce cortisol and the liver metabolic capacity were not compromised following TFM exposure, it is likely that their ability to cope with other stressors is not altered in the long-term.

Effects of water pH on the uptake and elimination of the piscicide, 3-trifluoromethyl-4-nitrophenol (TFM), by larval sea lamprey

Invasive sea lamprey (Petromyzon marinus) populations in the Great Lakes are controlled by applying the piscicide, 3-trifluoromethyl-4-nitrophenol (TFM), to infested streams with larval sea lamprey (ammocoetes). While treatment mortality is >90%, surviving lamprey, called residuals, can undermine control efforts. A key determinant of TFM effectiveness is water pH, which can fluctuate daily and seasonally in surface waters. The objectives of this research were to evaluate the influence of pH on the uptake, elimination, and accumulation of TFM by larval sea lamprey using radio-labeled TFM (¹⁴C-TFM), when exposed to a nominal concentration of 4.6mgTFML^-1 or 7.6mgTFML^-1, 3h or 1h, respectively. TFM uptake rates were approximately 5.5-fold greater at low pH (6.86) compared to the high pH (8.78), most likely due to the unionized, lipophilic form of TFM existing in greater amounts at a lower pH. In contrast, elimination rates following the injection of 85nmolTFMg^-1 body mass were 1.7-1.8 fold greater at pH8.96 than at pH6.43 during 2-4h of depuration in TFM-free water. Greater initial excretion rates at pH8.96 were presumably due to predicted increases in outward concentration gradients of un-ionized TFM. The present findings suggest that TFM is mainly taken-up in its un-ionized form, more lipophilic form, but there is also significant uptake of the ionized form of TFM via an unknown mechanism. Moreover, we provide an explanation to how small increases in pH can undermine lampricide treatment success increasing residual lamprey populations.

Exposure to the lampricide 3-trifluoromethyl-4-nitrophenol results in increased expression of carbohydrate transporters in Saccharomyces cerevisiae

The lampricide 3-trifluoromethyl-4-nitrophenol (TFM) is used to control sea lamprey (Petromyzon marinus) populations in freshwater lakes. Although TFM can have sublethal and lethal effects, little is known about gene expression changes with TFM exposure. Microarray analysis was used to determine differential gene expression over 4 h of exposure in Saccharomyces cerevisiae. Among the most significantly up-regulated genes were regulators of carbohydrate transport, including HXT1, HXT3, HXT4, IMA5, MIG2, and YKR075C. Environ Toxicol Chem 2016;35:1727-1732. © 2015 SETAC.

Effects of Lampricide on Olfaction and Behavior in Young-of-the-Year Lake Sturgeon (Acipenser fulvescens)

The lampricide, 3-trifluoromethyl-4-nitrophenol (TFM), is a primary component to sea lamprey control in the Laurentian Great Lakes. Though the lethal effects of TFM are well-known, the sublethal effects on fishes are virtually unknown. Here we studied the effects of TFM on the olfactory capabilities and behavior of young-of-the-year (YOY) lake sturgeon (Acipenser fulvescens). At ecologically relevant concentrations of TFM there was reduced olfactory response to all three cues (l-alanine, taurocholic acid, food cue) tested, suggesting that TFM inhibits both olfactory sensory neurons tested. Sturgeon exposed to TFM also showed a reduced attraction to the scent of food and reduced consumption of food relative to unexposed fish. Exposed fish were more active than control fish, but with slower acceleration. Fish were able to detect the scent of TFM, but failed to avoid it in behavioral trials. The connection between neurophysiological and behavioral changes, and the commonality of habitats between sturgeon and lamprey ammocoetes, suggests that there may be effects at the ecosystem level in streams that undergo lamprey control treatments.

The effects of the lampricide 3-trifluoromethyl-4-nitrophenol (TFM) on fuel stores and ion balance in a non-target fish, the rainbow trout (Oncorhynchus mykiss)

The pesticide 3-trifluoromethyl-4-nitrophenol (TFM) is used to control sea lamprey (Petromyzon marinus) populations in the Great Lakes through its application to nursery streams containing larval sea lampreys. TFM uncouples oxidative phosphorylation, impairing mitochondrial ATP production in sea lampreys and rainbow trout (Oncorhynchus mykiss). However, little else is known about its sub-lethal effects on non-target aquatic species. The present study tested the hypotheses that TFM exposure in hard water leads to (i) marked depletion of energy stores in metabolically active tissues (brain, muscle, kidney, liver) and (ii) disruption of active ion transport across the gill, adversely affecting electrolyte homeostasis in trout. Exposure of trout to 11.0mgl(-1) TFM (12-h LC50) led to increases in muscle TFM and TFM-glucuronide concentrations, peaking at 9h and 12h, respectively. Muscle and brain glycogen was reduced by 50%, while kidney and muscle lactate increased with TFM exposure. Kidney ATP and phosphocreatine decreased by 50% and 70%, respectively. TFM exposure caused no changes in whole body ion (Na(+), Cl(-), Ca(2+), K(+)) concentrations, gill Na(+)/K(+) ATPase activity, or unidirectional Na(+) movements across the gills. We conclude that TFM causes a mismatch between ATP supply and demand in trout, leading to increased reliance on glycolysis, but it does not have physiologically relevant effects on ion balance in hard water.

Analysis of genome survey sequences and SSR marker development for Siamese Mud Carp, Henicorhynchus siamensis, using 454 pyrosequencing

Siamese mud carp (Henichorynchus siamensis) is a freshwater teleost of high economic importance in the Mekong River Basin. However, genetic data relevant for delineating wild stocks for management purposes currently are limited for this species. Here, we used 454 pyrosequencing to generate a partial genome survey sequence (GSS) dataset to develop simple sequence repeat (SSR) markers from H. siamensis genomic DNA. Data generated included a total of 65,954 sequence reads with average length of 264 nucleotides, of which 2.79% contain SSR motifs. Based on GSS-BLASTx results, 10.5% of contigs and 8.1% singletons possessed significant similarity (E value < 10(-5)) with the majority matching well to reported fish sequences. KEGG analysis identified several metabolic pathways that provide insights into specific potential roles and functions of sequences involved in molecular processes in H. siamensis. Top protein domains detected included reverse transcriptase and the top putative functional transcript identified was an ORF2-encoded protein. One thousand eight hundred and thirty seven sequences containing SSR motifs were identified, of which 422 qualified for primer design and eight polymorphic loci have been tested with average observed and expected heterozygosity estimated at 0.75 and 0.83, respectively. Regardless of their relative levels of polymorphism and heterozygosity, microsatellite loci developed here are suitable for further population genetic studies in H. siamensis and may also be applicable to other related taxa.

Zebrafish: a model animal for analyzing the impact of environmental pollutants on muscle and brain mitochondrial bioenergetics

Mercury, anthropogenic release of uranium (U), and nanoparticles constitute hazardous environmental pollutants able to accumulate along the aquatic food chain with severe risk for animal and human health. The impact of such pollutants on living organisms has been up to now approached by classical toxicology in which huge doses of toxic compounds, environmentally irrelevant, are displayed through routes that never occur in the lifespan of organisms (for instance injecting a bolus of mercury to an animal although the main route is through prey and fish eating). We wanted to address the effect of such pollutants on the muscle and brain mitochondrial bioenergetics under realistic conditions, at unprecedented low doses, using an aquatic model animal, the zebrafish Danio rerio. We developed an original method to measure brain mitochondrial respiration: a single brain was put in 1.5 mL conical tube containing a respiratory buffer. Brains were gently homogenized by 13 strokes with a conical plastic pestle, and the homogenates were immediately used for respiration measurements. Skinned muscle fibers were prepared by saponin permeabilization. Zebrafish were contaminated with food containing 13 μg of methylmercury (MeHg)/g, an environmentally relevant dose. In permeabilized muscle fibers, we observed a strong inhibition of both state 3 mitochondrial respiration and cytochrome c oxidase activity after 49 days of MeHg exposure. We measured a dramatic decrease in the rate of ATP release by skinned muscle fibers. Contrarily to muscles, brain mitochondrial respiration was not modified by MeHg exposure although brain accumulated twice as much MeHg than muscles. When zebrafish were exposed to 30 μg/L of waterborne U, the basal mitochondrial respiratory control ratio was decreased in muscles after 28 days of exposure. This was due to an increase of the inner mitochondrial membrane permeability. The impact of a daily ration of food containing gold nanoparticles of two sizes (12 and 50 nm) was investigated at a very low dose for 60 days (40 ng gold/fish/day). Mitochondrial dysfunctions appeared in brain and muscle for both tested sizes. In conclusion, at low environmental doses, dietary or waterborne heavy metals impinged on zebrafish tissue mitochondrial respiration. Due to its incredible simplicity avoiding tedious and time-consuming mitochondria isolation, our one-pot method allowing brain respiratory analysis should give colleagues the incentive to use zebrafish brain as a model in bioenergetics. This article is part of a Directed Issue entitled: Bioenergetic dysfunction, adaptation and therapy.