Article pubs.acs.org/est
Effects of Lampricide on Olfaction and Behavior in Young-of-theYear Lake Sturgeon (Acipenser f ulvescens) Kathrine Sakamoto,† William A. Dew,‡,§ Stephen J. Hecnar,† and Gregory G. Pyle*,‡ †
Department of Biology, Lakehead University, 955 Oliver Road, Thunder Bay, Ontario P7B 5E1, Canada Department of Biological Sciences, University of Lethbridge, 4401 University Drive, Lethbridge, Alberta T1K 3M4, Canada § Department of Biology, Trent University, 2140 East Bank Drive, Peterborough, Ontario K9J 7B8, Canada ‡
ABSTRACT: 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 f ulvescens). 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.
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INTRODUCTION Fishes rely on olfaction to support a number of essential behaviors related to survival, growth, and reproduction, such as evaluating predation risk, finding food, and identifying appropriate potential mates.1−3 Recent studies have demonstrated that fishes’ olfactory systems are vulnerable to environmental toxicants, such as metals and pesticides.4−7 However, the effects of the lampricide 3-trifluoromethyl-4nitrophenol (TFM) on fishes olfaction have not been studied. Impairment of olfactory function can lead to a failure to perceive and respond to important chemosensory cues, which in turn can lead to maladaptive behaviors.7−10 It is important to understand the connection between the impairment of a physiological function such as olfaction and related modifications in behavior to better comprehend the impacts of the toxicant.11−13 A TFM-based sea lamprey control program was initiated in streams around Lake Superior in 1958 to eliminate sea lamprey (Petromyzon marinus) from the upper Laurentian Great Lakes. This program was later expanded to the other Great Lakes. Sea lamprey caused a dramatic reduction in the lake trout (Salvelinus namaycush) commercial fishery from 1938 to 1954, and eventually led the collapse of this fishery in 1959.14 Other Great Lakes fishes were also parasitized by sea lamprey, including lake whitefish (Coregonus clupeaformis), catostomids (Catostomus spp.), walleye (Sander vitreum) and rainbow trout (Oncorhynchus mykiss). Although several sea © XXXX American Chemical Society
lamprey control measures were developed and attempted, such as mechanical devices and electrical shock, most were expensive, difficult to implement, and largely ineffective. After screening more than 6000 candidate chemicals for sea lamprey control, TFM was found to be a selective sea lamprey larvicide with several other desirable characteristics.15 Sea lamprey control today still relies primarily on TFM, supplemented with 2′, 5-dichloro-4′-nitrosalicylanilide (called Bayluscide or niclosamide) to increase the effectiveness,16 and barriers in streams to reduce the amount of lampricide needed by blocking access to spawning areas.17 Lampricide treatments occur in approximately 316 tributaries to the Great Lakes, averaging 34,120 kg/yr of TFM from 1995 to 1999.18 Although TFM is selectively toxic to lampreys, some other fishes may be killed.19 Lake sturgeon (Acipenser f ulvescens), black bullhead (Ameiurus melas), channel catfish (Ictalurus punctatus), white suckers (Catostomus commersonii), longnose suckers (Catostomus catostomus), and northern pike (Esox lucius) are among the most sensitive.19,20 Notable lampricideinduced mortalities in Great Lakes tributaries include five instances of 10 000−30 000 sucker mortalities, two instances of 1000 and 5000 walleye mortalities, one instance each of 12 500 Received: March 1, 2016 Revised: March 11, 2016 Accepted: March 16, 2016
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DOI: 10.1021/acs.est.6b01051 Environ. Sci. Technol. XXXX, XXX, XXX−XXX
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response to standard chemosensory stimuli (L-alanine, taurocholic acid (TCA), and food cues), the behavioral response to food cues, food consumption, and activity levels. In addition, we tested whether or not YOY lake sturgeon can detect and avoid TFM, running trials both under lit and darkened conditions to determine if any measurable response to TFM was in response to visual or olfactory sensory input.
northern pike, 5000 carp, 10 000 brown bullheads, and 2000 brown trout mortalities.19 High mortality of small forage fishes in streams has occasionally occurred as well.19 Stonecat (Noturus f lavus) have undergone a dramatic depletion in the tributaries of the southwest corner of Lake Superior correlated with lampricide treatments.19 Trout-perch (Percopsis omiscomaycus), logperch (Percina caprodes), bullhead (Ictalusus spp.) and mudminnow (Umbra limi) are also sometimes adversely affected by lampricides.19 Juvenile lake sturgeon less than 1 cm long are more sensitive to TFM than lamprey ammocoetes in laboratory exposures,21 and exposure to environmentally relevant concentrations of TFM by young-of-the-year (YOY) lake sturgeon has caused 20−50% mortality.20,22 The mortality of sea lamprey ammocoetes by TFM is caused by an impairment of ATP supply.23−25 Exposure to TFM also caused an impairment of ATP supply in rainbow trout.26 Energy stores were found to return to normal within 4−12 h post TFM exposure in sea lamprey ammocoetes.25 Although the lethal effects on other fishes have been well studied, there is only one known study on the sublethal effects on nontarget fishes, which focuses on the effects of TFM on the growth of lake sturgeon and rainbow trout, predator avoidance of fathead minnows (Pimephales promelas) and avoidance of TFM by rainbow trout.27 McDonald and Kolar21 recommend characterization of the sublethal effects of TFM exposure to nontarget fishes in their paper describing research priorities for the use of lampricides in the sea lamprey control program. In practice, TFM (sometimes together with niclosamide) is applied to streams as a single block of chemical, typically over a 12 h period at concentrations up to 1.5 times the minimal lethal concentration (MLC) required to kill 99.9% of lamprey ammocoetes.18,21,22 The color of TFM is bright yellow and has a distinct odor to humans. The application of TFM is usually conducted in July or August, but may also occur in September or October for a variety of reasons such as to protect lake sturgeon by allowing them to reach a larger size before treatment.28,29 Application procedures suggest no particular time of day or night.30 The aim of this study was to investigate sublethal effects of TFM on olfaction and behavior in YOY lake sturgeon. Sturgeons are known to have poor vision and well-developed chemosensory senses, including olfaction.31,32 Lake sturgeon populations have been declining over the entirety of their range owing primarily to overharvesting and habitat degradation and depletion.33 Lake sturgeon in the Great Lakes is classified as threatened by the Committee on the Status of Species at Risk in Ontario and the Committee on the Status of Endangered Wildlife in Canada.34 Recommended management needs to rehabilitate the species include strict control over harvest quotas, the rehabilitation of spawning stock, pollution control, and habitat restoration.35 Habitat restoration refers to areas where critical spawning and rearing habitat has been blocked, destroyed, or altered.35 Juvenile lake sturgeon habitat overlaps with the preferred habitat of sea lamprey larvae (ammocoetes); that is, relatively low-flowing stream segments with fine substrates in shallow to moderate depths.33,34,36,37 Once suitable habitat is identified by lake sturgeon, their local home range is relatively short, often within about a 2 km reach.33 This habitat overlap and narrow home range places lake sturgeon at risk of lampricide exposure from routine lamprey eradication programs. Our study measured the effects of exposure to environmentally relevant concentrations of TFM on the olfactory
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EXPERIMENTAL PROCEDURES Research was conducted on YOY lake sturgeon at the Black River Streamside Sturgeon Rearing Facility near Onaway, Michigan during August of 2013 and 2014, under the approval of the Lakehead University Animal Care Committee (protocol numbers 10−2013 and 09−2014) and was Canadian Council on Animal Care (CCAC) compliant. Sturgeon lengths ranged from 85 to 163 mm (mean 127.0 ± 18.1 mm standard deviation [SD]) and weights ranged from 2.7 to 18.5 g (mean 8.5 ± 3.1 g SD); n = 173. Water temperatures during 2013 ranged from 21.1 to 22.8 °C and from 17.2 to 17.8 °C during 2014. During trials, all water was temperature matched to hatchery conditions. The alkalinity of the water was 180 mg/L CaCO3, determined by titration with 0.02 N hydrochloric acid using methods described in Pyle et al.38 The pH was 8.1 without aeration, and varied slightly from 8.5 to 8.7 with aeration. Fish were fed bloodworms three times per day, which was reduced to once per day 2 days prior to the commencement of experiments. TFM Exposures. Fish were exposed to TFM (Alfa Aesar, Chicago, IL) in aerated tanks containing 5 L of water. The solubility of TFM is 5000 ppm at 25 °C.39 The amount of TFM used replicated 1.0 × MLC used by Sea Lamprey Control to kill 99.9% of larval sea lamprey, which is dependent on the alkalinity and pH of the water, as described in Bills et al.40 Although this exposure concentration is less than what is generally applied in the field, it is the target minimum level for lampricide applications after attenuation and dilution from back eddies and groundwater sources.21,22 The toxicity of TFM, which is an acid, increases with lower pH of the water.41 The concentration of TFM used for fish exposures ranged from 6.5 mg/L (pH 8.5) to 8.6 mg/L (pH 8.7). Fish remained in the exposure bath for 12 h to simulate the amount of time that fish may be exposed to TFM during a typical stream treatment. All assays were conducted after the exposures, with no additional TFM added during the trials. All experiments and interpretations were based on nominal TFM concentrations. Electro-Olfactography (EOG) Experiments. Electroolfactography (EOG) was used to measure the response to various odorants of olfactory sensory neurons (OSNs), which are located in the olfactory epithelium of the paired olfactory rosettes found between the upper jaw and eyes of the fish. The olfactory rosettes are confined within the olfactory chamber, with water from the external environment entering and exiting via the anterior and posterior nares. The OSNs are the boundary between the external environment and neurological system, rendering them a probable target for waterborne contaminants. Electro-olfactography is an electrophysiological technique that determines the amplitude of electrical activity of the OSNs to an odor, registering the negative electrical potential.42 An inhibition of the EOG response to standard chemosensory cues in TFM-exposed sturgeon would indicate impairment at the olfactory epithelium. The EOG methods were modified from those described by Green et al.5 Modifications were made to the EOG method for B
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allowing fish access to the entire tank. Cues were randomly assigned to one end of the tank for each trial to control for tank end bias. Fish behavior was observed for 10 min following the removal of the acclimation chamber, with the location of the fish in the tank being recorded every 10 s (stimulus end, blank end, or middle of tank). Any fish that was recorded in the middle of the tank for half of the trial or longer was eliminated from the experiment, as it had not clearly made a choice. To determine the behavioral response of YOY sturgeon to a food cue, a solution made with 0.35 g/L frozen bloodworms was prepared as described above. The bloodworm-scented water was placed into an intravenous (IV) bag (JorVet, Loveland, CO) and dripped into one end of the tank at a rate of 3.5−5.0 mL/min via 6 mm (i.d.) silicone airline tubing. An IV bag filled with a blank cue, which was prepared using the same procedure as that used for the food cue but contained no bloodworms, and was delivered at the same rate in the other end of the tank. The end of the tank that received each cue was randomly assigned. To study the effects of TFM on food consumption, a YOY lake sturgeon (n = 10) was placed in a 5 L feeding chamber containing aerated hatchery water and 2.0 g of bloodworms. Fish were left to feed for 1.5 h before being removed from the chamber along with any faeces. The remaining food was filtered out of the water through a sieve then reweighed. The food absorbed water during the feeding period resulting in some final weights being slightly higher than the initial weight of food. The amount of time the control and exposed fish were active, as well as their acceleration and velocity, were compared using the video recordings from the food cue trials, analyzed with LoliTrack software, version 4.1.0, (Loligo Systems, Tjele, Denmark). The amount of active time was measured as percent time active, determined by dividing the time moving by the total time of the trial. Fish activity was defined as when the fish moved a distance larger than a pixel between video frames and was measured as a percentage of the total time. The average acceleration was calculated based on forward fish movement between video frames, in cm/s2. The average velocity was calculated from the speed of forward movements between video frames, in cm/s. To study the behavioral response to TFM, a behavioral maze was used to mimic an encounter with a block of TFM (i.e., a continuous area of chemical extending to both sides and one end of the rectangular tank) in one end of the tank, similar to a typical TFM stream treatment described previously. The cue was prepared and delivered to produce a block of TFM that would have a concentration of 1 × MLC when it dispersed to one-half of the tank. An initial stock solution was prepared using 92.5 mg of TFM in one liter of hatchery water. For each trial, 100 mL of the stock solution was poured into one end of the tank and allowed to disperse toward the middle of the tank. A 100 mL water blank, consisting of hatchery water, was simultaneously added to the opposite end of the tank. The acclimation chamber was removed when the TFM had spread about two-thirds of the way toward the middle of the tank so that the concentration of TFM encountered would be no greater than 1.5 × MLC, the maximum amount that may be encountered in the field. Trials simulating daylight conditions, when color and odor may influence behavior, were conducted with the laboratory lights on. Trials simulating darkness, when only odor may influence behavior, were conducted in the dark. A monochrome camera with infrared lighting was hung over
use with YOY lake sturgeon, as all animals needed to be resuscitated postexperiment given their at-risk status. The anesthetic bath was prepared using the lowest concentration of MS-222 that anaesthetized the fish, 100.0 mg/L buffered with sodium bicarbonate to a pH of 7.4. Anaesthesia was maintained in the gill perfusion water at a concentration of 50.0 mg/L MS222. Toxicants may impair specific classes of OSNs in the olfactory epithelium.6 To study the effect of TFM on microvillous sensory neurons, L-alanine was used as an odor cue in EOG assays. Multiple studies report that L-alanine is effective at inducing food searching behavior in Persian and Russian sturgeon (Acipenser gueldenstadtii), Siberian sturgeon (A. baerii), green sturgeon (A. medirostris), and stellate sturgeon (Acipenser stellatus).31,43 The bile salt taurocholic acid (TCA) was used to test the ciliated sensory neurons, which are tuned to migration and alarm cues.44,45 The EOG response to 10−3 M L-alanine, 10−4 M TCA, a food cue made from blood worms (described below), 17.9 μM TFM (3.7 mg/L at water pH 8.1), and a water blank were measured. These concentrations of L-alanine and TCA have been used by others in olfactory research on fishes.6,46 The amount of TFM replicated 1.0 × MLC used by Sea Lamprey Control to kill 99.9% of larval sea lamprey.40 The food cue was prepared by stirring 0.5 g of frozen bloodworms in 1 L of hatchery water for 30 min and filtering through aquarium polyester filter wool to remove any particulate material. The order of cue delivery was randomized with a minimum of 90 s between cue deliveries to mitigate attenuation from overstimulation by any single chemosensory cue. Each cue was presented a minimum of three times to a fish and averaged. For all experiments except the EOG response to TFM (which is presented as raw EOG value in mV), the response to each cue was blank-corrected by subtracting the EOG response elicited by the blank. The blanked-corrected value for each cue for a TFM-exposed fish was corrected against the value for the same cue for a control fish. The corrected values were then averaged across fish. For each cue, the mean corrected EOG response (E) was determined using the following formula: E=
∑
( ba ) c
(1)
where a = the mean blank-corrected EOG response (mV) of the test fish; b = the mean EOG response (mV) of the control fish to the corresponding odor cue; c = the number of test fish. Behavioral Experiments. All behavioral maze trials utilized a 16 × 65 × 15 cm (W × L × H) rectangular tank divided into three equally sized zones consisting of two ends and a central acclimation zone. Prior to each trial, tanks were washed with Sparkleen (Fisher Scientific, Fair Lawn, NJ) detergent and rinsed thoroughly with hatchery water. Each tank was then filled with 5 L of fresh hatchery water and the tank was placed into a larger flow-through tank to maintain temperature. Fish were held in the acclimation zone for 5 min to allow the animal to acclimate to tank conditions and to restrict access to the distal reaches of the tank where the chemosensory cues would ultimately be delivered. A camera was placed above the tank to observe and record the fish behavior and a fabric sheet was placed over the entire unit to isolate the fish from any movement outside of the tank. Chemosensory cues were delivered to the distal ends of the tank and were allowed to dissipate for at least 30 s prior to C
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Figure 1. Effects of TFM exposure on YOY lake sturgeon. (A) Mean corrected EOG response to 10−3 M L-alanine, 10−4 M TCA, and food cue. (B) Behavioral response comparing the attraction to a food cue compared to a water blank cue. An asterisk denotes a significant difference between the time spent in the food cue arm versus the water blank arm. (C) Mean final weight of food remaining after 1.5 h of feeding. An asterisk denoted a significant difference. Error bars denote ± standard error of the mean.
Figure 2. Effects of TFM exposures on the (A) amount of active time, (B) acceleration, and (C) velocity of YOY lake sturgeon (n = 20) compared to controls (n = 16). An asterisk denotes a significant difference between control and exposed fish. Data are expressed as the mean ± one standard error.
Figure 3. Electro-olfactogram and behavioral response of YOY lake sturgeon to TFM. (A) The mean corrected EOG response to TFM compared to a water blank. An asterisk denotes a significant difference. (B) The behavioral response to a TFM cue compared to a water blank cue in light and dark conditions, comparing the amount of time spent in each cue arm. All fish were tested in hatchery water. Error bars denote ± standard error of the mean.
significance was set at α = 0.05. Data presented are means ± standard errors, unless otherwise stated.
the tank to record the response to TFM during both light and dark conditions. Statistical Analysis. Statistical analysis was performed using IBM SPSS Statistics software (IBM, Armonk, New York). The EOG responses to L-alanine, TCA, and food were measured in the same fish and analyzed using a MANOVA to compare responses from exposed and unexposed sturgeon. Food consumption trials compared the final weight of the remaining food at the end of the trial, between exposed and unexposed animals using t tests for independent samples. Behavioral maze trials and EOG response to TFM were analyzed using t tests for paired samples, except when data were not normally distributed, and then a Wilcoxon signed rank test was used. Any differences in the velocity, acceleration and percent of time active between the control and exposed fish were tested using independent t tests. For all analyses,
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RESULTS The YOY sturgeon exposed to TFM showed a diminished EOG response to L-alanine (52% relative to controls), TCA (64%) and a food cue (80%), which were only marginally significant due to small sample sizes and relatively high variation in control animal EOG responses (F(2, 4) = 5.97, p = 0.06 (Figures 1A)). When given the choice between a food cue or hatchery water, control fish spent 66% more time in the end of the tank containing the food cue relative to the end containing the water blank (t13 = 2.64, p = 0.02, Figure 1B). In contrast, fish exposed to TFM showed no preference for either end of the tank (t19 = 0.06, p = 0.95, Figure 1B). In food D
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time exposed fish were active did not increase the encounters and ingestion of food, which would have produced contrary results. Sturgeons are known to have poor vision and rely primarily on other senses to find food.31,32 Nevertheless, vision or gustation could have played some role in finding food during the food consumption trials. If this was the case then TFM may have impaired vision or gustation as well. Further study is required to confirm if diminished olfaction is the physiological cause of the observed reduction in food consumption. Middaugh et al.27 found no significant difference in growth over 14 days in sturgeon exposed to TFM, although the concentrations of TFM used in exposures were less than 1 × MLC used in our study. Further studies are needed to determine if the effects of TFM on food detection and consumption are short-lived, or whether long-term detrimental effects occur at 1 × MLC. There are few studies on the effects of other aquatic toxicants on behavioral traits of fishes. Juvenile rainbow trout had an impaired alarm response after exposure to copper nanoparticles, eliminating their typical freeze response and reducing swimming activity.9 Mummichog (Fundulus heteroclitus) embryos exposed to methylmercury swam greater distances, which increased predation, potentially by attracting the predator to the increased activity.10 Reduced swimming behavior has also been related to failure to avoid predation in this same species.51 Exposure of Persian sturgeon (Acipenser persicus) fingerlings to environmentally relevant levels of diazinon exhibited muscle paralysis, rapid operculum movement, erratic swimming, increased aggression, a loss of body balance and changes in hematological parameters.52 Birceanu et al.24 found the mechanism of toxicity of TFM in sea lamprey ammocoetes to be a reduction in glycogen in the liver and brain, leading to death. The effect of TFM was similar on rainbow trout in another study by Birceanu et al.,53 but did not cause death at comparable concentrations. The change in swimming behavior found in YOY lake sturgeon in this study may be related to a physiological effect of TFM. The modifications to swimming behavior may increase their risk of predation by attracting attention to increased movement and reducing their ability to escape due to slower acceleration. Further research is warranted to study the cause and duration of these behavioral changes. Lack of avoidance of TFM was not an expected response, as most metals and pesticides cause an avoidance response in fishes.7 However, a few studies found no reaction to environmentally relevant concentrations of toxicants, as found in this study. Sheepshead minnow (Cyprinodon variegatus) had no reaction to Dursban (chlorpyrifos), Malathion or Sevin (carbaryl) insecticides54 or Aroclor (PCB mix).55 Mosquitofish (Gambusia aff inis) had no reaction to the insecticides Endrin56 and DDT.57 Golden shiners (Notemigonus crysoleucas) had no reaction to either cadmium or selenium.58 The inability to avoid a toxicant may result in real biological effects. In this case, YOY lake sturgeon may not avoid exposure to TFM and subsequent injury, even when given a choice, resulting in abnormal behavior that could impact their growth and survival. The duration of these effects of TFM on YOY lake sturgeon is unknown at this time. All assays were conducted in clean water and produced measurable changes in EOG response and behavior, demonstrating that olfactory recovery was not immediate. Other studies have found a wide variation in the recovery of fishes to toxicants. Yellow perch (Perca f lavescens) showed a rapid olfactory recovery from metal contaminated
consumption assays, fish exposed to TFM ate 36% less than controls (t18 = 6.55, p < 0.01; Figure 1C). Activity analysis revealed an increased amount of activity with a decrease in acceleration and velocity in exposed fish. The fish exposed to TFM were 79% more active (t32 = −2.96 p < 0.01; Figure 2A), but accelerated 19% more slowly (t32 = 2.01 p = 0.05; Figure 2B) and had a 16% slower velocity (t32 = 1.83 p = 0.08; Figure 2C). Fish had 120% greater EOG responses to TFM, compared to a water blank (t2 = −6.00, p = 0.03; Figure 3A). However, when presented with TFM or a water blank, there was no significant difference between the time fish spent in either end of the tank for both the trials in daylight (t15 = 0.470, p = 0.64, Figure 3B) and in darkness (t16 = −1.419, p = 0.175, Figure 3B).
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DISCUSSION Our study is the first to demonstrate that TFM has an effect on the olfactory responses and behaviors of fish. These results are consistent with the known effects of other contaminants on the olfactory response of fishes. For example, environmentally relevant copper concentrations impaired olfaction in fathead minnows and reduced behavioral responses to food stimuli.5 An environmentally realistic mixture of pesticides reduced the EOG response of rainbow trout.47 The water-soluble herbicide glyphosate produced EOG reductions in coho salmon (Oncorhynchus kisutch).48 Although the effects of metals and organic pollutants have been studied for many years, there has been no research on the effects of TFM on any component of chemosensation in fishes. It is possible that other Great Lakes tributary fishes may be affected by TFM as well. Niclosamide, the other component to some lampricide assessments and treatments, has not been studied and may also have an impact on chemosensation and behavior. Further research is needed to fully understand and interpret the impacts of lampricide treatment on fishes behavior and ecosystem functioning. The specificity of L-alanine to microvillous OSNs and TCA to ciliated OSNs allowed us to determine that exposure to TFM at environmentally relevant concentrations caused impairment to both types of sensory neurons. However, not all pesticides and metals are toxic to both OSNs studied here. Nickel was found to impair microvillous OSNs, while copper impaired ciliated OSNs in fathead minnows and yellow perch.6 Impairment of both of these OSNs may increase the effect of TFM on the behavior of YOY lake sturgeon. Since microvillous OSNs are known to respond to amino acids49 related to food seeking behavior,45 the altered behavioral responses to the scent and consumption of food may be connected to the impairment of microvillous OSNs. The impaired EOG response to the food cue further supports this connection. Ciliated OSNs are known to respond to bile salts such as TCA,49 which are used in migration and alarm response.45 The impairment of ciliated OSNs to TCA raises concern that there may also be a reduced ability to detect predators and behavioral changes related to migration and alarm response. Sturgeon, among other fishes, are known to have a third type of OSN called “crypt cells”50 which respond to sex pheromones.45 Further work is required to determine if TFM affects chemosensory detection of sex cues and associated behaviors. The modified behavior of the TFM exposed fish in the food consumption trials cannot be definitively attributed to a loss of olfactory ability. The food was visually available and could be discovered by the fish by randomly encountering it when swimming in the tank. However, the increase in the amount of E
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Environmental Science & Technology lakes when exposed to clean water for only a few hours.46 In contrast, cadmium caused cell death in the olfactory tissue of developing zebrafish embryos (Danio rerio).59 Alkyl benzenesulfonate surfactants caused impaired olfaction in yellow bullhead (Ictalurus natalis) that was not repaired within 6 weeks of exposure.60 The duration of impaired olfactory and behavioral responses of YOY lake sturgeon from exposure to TFM needs to be determined so the full effects can be assessed. The degree and duration of impairment may vary with the age of the fish, and therefore also requires further study. The results of this research suggest that TFM has detrimental effects on the ability of lake sturgeon to perceive and interact with their environment. These impacts are in addition to the currently known effects from TFM and sea lamprey control, such as YOY mortality and loss of access to spawning habitat due to barriers.20,22,34 There are few examples of alien species that have been successfully eradicated once an invasion is well established.61 Habitat or ecosystem management is often prescribed as a holistic approach to alien invasive species by targeting the overall condition of the ecosystem.61 A better understanding of the impacts of TFM on stream ecosystems may lead to new methods to minimize the impacts of sea lamprey invasion while protecting physiology and behavior of sturgeon populations.
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AUTHOR INFORMATION
Corresponding Author
*E-mail:
[email protected]. Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS This research would not have been possible without the financial support from the Ontario Ministry of Natural Resources (OMNR) Species at Risk Branch SARRFO program, the Lake Superior Advisory Committee, Black Bay Fish and Game Club, Thunder Bay District Stewardship Council, Northwestern Ontario Sportsmen’s Alliance, North Shore Steelhead Association, Thunder Bay Salmon Association, and the North Lake Superior Graduate Thesis Award. Thanks to field assistants Karen Schmidt and Greg Kilroy. Special thanks to Dr. Edward Baker and Nathan Barton for their cooperation in providing sturgeon and accommodating this research at the Black River Streamside Hatchery.
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