After 2 hr of exposure, no cell death was observed at any of the concentrations used result not shown. Initially a stable baseline for OCR was established for 32 min, at which point the compounds were injected directly onto the cells in the XF24 analyzer chamber, and the changes in OCR were monitored for a further 2 hr.
As shown in Figure 2A , 3A , rotenone induced significant effects on basal OCR at concentrations of 1 nM with a rate of onset of inhibition which was dependent on the concentration. To better understand the relationship between cell viability and mitochondrial function, we have directly plotted the basal OCR versus cell viability by integrating the data from Figure 1B—F and Figure 3A—C.
The extent of rotenone induced cell death matches the extent of rotenone induced decrease in OCR. Using the XF24 analyzer, the mitochondrial oxygen consumption rate OCR was determined for 4 basal readings with 80, cells plated per well. Data are expressed as percent of the basal OCR prior to injection of neurotoxins. In some cases, the error bars are smaller than the symbols. Inhibition of mitochondrial respiration stimulates glycolysis and this can be detected by an increase in the rate of extracellular acidification ECAR.
Next we tested the effects of the inhibitors on ATP-linked and maximal respiration using the sequential addition of mitochondrial inhibitors as described previously [69] Figure 5A—C. The capacity of the respiratory chain to synthesize ATP under basal conditions can be estimated from the extent of decrease in OCR after the addition of oligomycin. The remaining OCR after the addition of oligomycin can be ascribed to proton leak or non-mitochondrial sources of oxygen consumption and varied between The values for proton leak are shown in Figure 4G—I for the three compounds.
Interestingly, rotenone decreased proton leak at 0. Interestingly, the behavior of all 3 compounds was markedly different. Rotenone at 0. To achieve this we have selected a dopaminergic cell line, SH-SY5Y, which has been used extensively as a model to test the effects of neurotoxins on cell function [45] , [70] — [85]. We have recently shown that the bioenergetic profile of differentiated SH-SY5Y cells possess many of the hallmarks of neurons including the presence of a bioenergetic reserve capacity [70].
All three neurotoxins have been tested in this cell model in a wide range of studies [45] , [72] , [75] , [76] , [80] , [81]. The differentiated forms of these cells have an active dopamine transporter although it may have a lower activity than in mesencephalic dopaminergic neurons, it has similar activity to that found in synaptosomes [45] , [72] , [85].
It is important to recognize that the relative potency may change depending on cell type and the levels of expression of DAT. Primary dopaminergic neurons from rodents may better resemble human dopaminergic neurons in terms of cellular properties used but unfortunately, cellular bioenergetic analysis requires homogeneous cell populations and this is a technical limitation to the use of mesencephalic neurons which are heterogeneous and are not easy to obtain in large numbers [86].
To gain more insight into the mechanisms of how these neurotoxins affect cellular bioenergetics, we assessed different aspects of the bioenergetic profiles [69]. The extent to which this decreases after a treatment can be ascribed to the inhibition in the cell of an ATP consuming process, inhibition of the ATP synthase or related proteins, or decreased ability of the electron transport chain to provide sufficient proton motive force to drive ATP synthesis.
The remaining OCR after the addition of oligomycin is ascribed to proton leak. In this parameter the 3 neurotoxins also showed different responses. Rotenone decreased proton leak even at 0. We have previously shown that increase ROS can cause an increase in proton leak consistent with the reported pro-oxidant effects of 6-OHDA [87].
Adding the proton ionophore FCCP removes the regulation of the proton motive force on basal respiration, and allows full activity of the respiratory chain to be realized depending on the substrate availability from cellular metabolism. The difference between basal and maximal OCR is termed the reserve or spare bioenergetic capacity and, in the absence of any other bioenergetic defects, can be used to service increased energy demands in the cell including increased oxidative stress [68] , [69].
Using this approach, we observed that rotenone exposure decreased maximal respiration and reserve capacity at 0. Specifically, inhibition of cellular respiration by rotenone results in the compensatory induction of glycolysis, loss of bioenergetic reserve capacity, activation of the apoptotic cascade and a strong correspondence between the doses which cause bioenergetic dysfunction and cell death.
The apoptotic pathway is not activated, and the doses which cause inhibition of mitochondrial function do not correspond well to cytotoxic doses. It is possible 6-OHDA impacts mitochondrial redox signaling without engagement of the major intra-mitochondrial metabolic pathways. Furthermore, a most recent study in the Journal of Neurochemistry [90] has shown that at doses clearly affecting mitochondrial function, there is a lack of correlation with superoxide generation.
We thank members of Dr. Zhang and Dr. Darley-Usmar laboratories for technical help and discussions. We thank Dr. Performed the experiments: SG JL. Browse Subject Areas? Click through the PLOS taxonomy to find articles in your field. Cell Viability Cell viability was measured first by Calcein AM assay and then confirmed using the trypan blue exclusion method.
Download: PPT. Energy substrate requirements of rat retinal pigmented epithelial cells in culture: relative importance of glucose, amino acids, and monocarboxylates. Osborne NN. Stimulatory and inhibitory actions of excitatory amino acids on inositol phospholipid metabolism in rabbit retina. Evidence for a specific quisqualate receptor subtype associated with neurones. Exp Eye Res. Endoplasmic reticulum stress and glycogen synthase kinase-3beta activation in apolipoprotein E-deficient mouse models of accelerated atherosclerosis.
Arterioscler Thromb Vasc Biol. Bradford MM. A rapid and sensitive method for the quantitation of microgram quantities of protein utilizing the principle of protein-dye binding. Anal Biochem. Cortopassi G Danielson S Alemi M Mitochondrial disease activates transcripts of the unfolded protein response and cell cycle and inhibits vesicular secretion and oligodendrocyte-specific transcripts.
Sodium 4-phenylbutyrate acts as a chemical chaperone on misfolded myocilin to rescue cells from endoplasmic reticulum stress and apoptosis. Calpain, not caspase, is the causative protease for hypoxic damage in cultured monkey retinal cells. Neurodegeneration produced by rotenone in the mouse retina: a potential model to investigate environmental pesticide contributions to neurodegenerative diseases.
J Toxicol Environ Health A. Transgenic mice expressing cyan fluorescent protein as a reporter strain to detect the effects of rotenone toxicity on retinal ganglion cells. Endoplasmic reticulum stress and the unfolded protein responses in retinal degeneration. Retinal ganglion cell death induced by endoplasmic reticulum stress in a chronic glaucoma model.
Brain Res. Increased expression of IRE1alpha and stress-related signal transduction proteins in ischemia-reperfusion injured retina. Clin Ophthalmol. Morphological and immunocytochemical characterisation of mixed glial cell cultures derived from neonatal canine brain. Res Vet Sci. Lactate released by Muller glial cells is metabolized by photoreceptors from mammalian retina. Glucose metabolism in freshly isolated Muller glial cells from a mammalian retina.
J Comp Neurol. Cultured retinal neuronal cells and Muller cells both show net production of lactate. Gething MJ.
Role and regulation of the ER chaperone BiP. Semin Cell Dev Biol. Inhibition of mitochondrial function induces an integrated stress response in oligodendroglia.
ATP regulates calcium leak from agonist-sensitive internal calcium stores. Transcriptional induction of genes encoding endoplasmic reticulum resident proteins requires a transmembrane protein kinase. Cell Death Dis. Endoplasmic reticulum stress signal impairs erythropoietin production: a role for ATF4. Am J Physiol Cell Physiol. Tsujimoto Y. Apoptosis and necrosis: intracellular ATP level as a determinant for cell death modes.
Cell Death Differ. Neurochem Res. Involvement of calpain in hypoxia-induced damage in rat retina in vitro.
Curr Eye Res. Arch Toxicol. Endoplasmic reticulum stress and alteration in calcium homeostasis are involved in cadmium-induced apoptosis. Cell Calcium. Lipton P. Ischemic cell death in brain neurons. Physiol Rev. Calpain mediates ischemic injury of the liver through modulation of apoptosis and necrosis.
Calpain: new perspectives in molecular diversity and physiological-pathological involvement. Calpain inhibitors and antioxidants act synergistically to prevent cell necrosis: effects of the novel dual inhibitors cysteine protease inhibitor and antioxidant BN and its pro-drug BN Calpain inhibitor MDL protects hypoxic-ischemic brain injury in neonatal rats by inhibition of both apoptosis and necrosis.
The multifaceted roles of glycogen synthase kinase 3beta in cellular signaling. Prog Neurobiol. Pharmacol Res. In addition to the liver, the heart and brain stem were chosen for gene expression profiling due to their high energy demand and the known neurotoxic effect of rotenone. By using this experimental design we intended to identify MOA-based biomarkers and provide enhanced mechanistic insights into the action of complex I inhibitors to improve the assessment of compounds in drug development.
The treatment of male rats with ppm rotenone through the diet resulting in a daily intake of Correspondingly, absolute organ weights of rotenone exposed animals were significantly reduced compared to control animals, which was especially the case for liver and kidneys. For a complete overview of body and organ weights see Supplementary Fig. S1 and Table S1. Histopathological investigations indicated no changes in kidneys, heart and brain, amongst many other organs evaluated.
However, liver, hematopoietic tissue and bone were identified as primary target organs by histopathological and other supporting investigations like gene expression profiling, hematology and FACS-analysis. Detailed findings are described below.
To determine the potency of complex I inhibition by rotenone after the different treatment durations, complex I activity was measured enzymatically in isolated liver mitochondria. Rotenone exposure induced a strong and significant decrease in complex I activity Fig. S2 , indicating that the inhibition by rotenone was maintained even after isolation of the mitochondria.
Histopathological findings in the liver summarized in Table 1 revealed a distinct loss of glycogen in hepatocytes and condensation of the cytoplasm, most noticeably after 1 and 3 days of rotenone treatment Fig. In addition, decreased granulation of the rough endoplasmic reticulum was observed, accompanied by substantial alterations in cytoplasmic morphology. These changes were also found in the day treatment group. The histopathologically observed glycogen loss was consistent with an enzymatically determined significant decrease of the glycogen content in the livers of rotenone treated relative to control animals at every time point Fig.
Overall, this suggests a hypocaloric status induced by rotenone exposure. Together, the liver-associated alterations summarized above, and increased urea and glutamate dehydrogenase GLDH and decreased alkaline phosphatase APh levels Fig.
For a complete overview of clinical chemistry parameters see Supplementary Table S2. A — C Histopathological changes in the liver of rats treated with ppm rotenone for 3 B and 14 days C compared to control A. Bone marrow adipocytes started to increase after 3 days of dosing, indicating bone marrow depletion Fig.
One primary target of rotenone seemed to be erythropoiesis. In the spleen, extramedullary erythropoiesis was reduced in all animals after 3 days of treatment Table 1. After 14 days, it was observed in all treated animals again with moderate severity, but also in three of five control animals with minimal severity.
The latter may be related to the age of the animals used here, since extramedullary hematopoiesis declines with increasing age in rats FACS-analysis of femoral bone marrow indicated a significant increase in the erythroid cell lineage with a shift towards more mature forms over time Fig. In addition, red progenitor cells, myeloid and lymphoid cells were significantly diminished notably after 14 days of rotenone treatment, confirming general bone marrow depletion Fig. A — C Histopathological changes in the bone marrow of rats treated with ppm rotenone for 3 B and 14 days C compared to control A , indicating decreased bone marrow cellularity and an increase in adipocytes after 3 days of treatment B , with increased severity after 14 days C.
F , G Representative FACS plots of immature nucleated cells and mature non nucleated cells blue circle of a control animal F and a rotenone treated animal after 14 days G. The blue arrow indicates a shift towards more mature erythroid forms. The effects of rotenone on hematopoietic cells overall were investigated through the examination of red and white blood parameters and thrombocytes in blood.
Significant increases in erythrocyte count, hemoglobin concentration and hematocrit were observed after 14 days in animals treated with rotenone compared to the control group Fig. Moreover the number of reticulocytes was significantly decreased after 3 days in rotenone treated rats Fig. These findings confirm the histopathological and FACS observations, revealing an effect of rotenone on erythropoiesis. For a complete overview of hematology parameters see Supplementary Table S3.
In the femur and tibia, minor changes in the growth plate were already encountered after 3 days of rotenone treatment. Dilation of subchondral blood sinuses, a slightly reduced height of the physis and reduction of spongiosa formation in the subchondral plate indicated the beginning of growth arrest and atrophy of the growth plate. After 14 days of treatment, a distinct suppression of the proliferative and hypertrophic zone of the cartilage was visible leading to a thin growth plate, cessation of primary enchondral ossification in the subchondral plate and a decrease in subsequent secondary ossification.
No regressive changes were noted, and the growth zones rather resembled those in older rats, but with less trabecular stability in the subchondral plate Fig. These histopathological findings are summarized in Table 1.
Gene Expression Analysis was performed in several organs to examine pathways and functions affected by rotenone at the molecular level. The liver and heart were chosen due to the high metabolic activity and the high energy demand, respectively. Accordingly, in our short term study we expected gene expression changes rather in the brain stem as compared to other brain regions.
After the analysis of the whole transcriptome, the strongest rotenone-induced effects on gene expression were observed in liver deregulated genes compared to heart deregulated genes and brain stem 52 deregulated genes Fig. This finding supports the results reported above, proposing the liver as a primary target organ of rotenone.
Only a small number of genes were deregulated in the brain stem after rotenone treatment compared to the liver and heart Fig. For interpretation the deregulated genes were assigned to different biochemical categories and subcategories in the context of the main biological functions a complete overview of genes assigned to such categories is given in Supplementary Table S4. The major functions Fig.
Particularly genes encoding mitochondrial complex I subunits were up-regulated primarily in the liver Fig. An increased expression of genes associated with fatty acid oxidation Fig. Concerning the latter, genes encoding mitotic spindle components were down-regulated.
Genes encoding cholesterol biosynthesis enzymes were initially down-regulated after 1 and 3 days of rotenone treatment, but were subsequently up-regulated after 14 days Fig. However, several genes associated with bile acid synthesis were up-regulated throughout in the liver tissue Fig.
Genes known to be induced in response to oxidative stress were up-regulated in the liver, heart and brain stem Fig. However, Hif1 target genes and Hyou1 Hypoxia up-regulated 1 , usually induced by hypoxia, were down-regulated Fig. A rather unexpected down-regulation of genes encoding glycolysis enzymes in the liver and heart Fig.
In addition, the expression level of the gene encoding GAA Lysosomal alpha-glucosidase , which is essential for breakdown of glycogen to glucose in lysosomes, was increased in the liver. Furthermore, genes belonging to the insulin pathway were down-regulated in the liver and heart Fig.
Interestingly genes associated with hematopoiesis and the oxygen carrier hemoglobin were down-regulated after 3 and 14 days of treatment in the liver and heart Fig. Another interesting finding was the up-regulation of Igfbp2 insulin-like growth factor binding protein 2 mRNA after all durations of treatment and the down-regulation of Igf1 insulin-like growth factor 1 mRNA after 3 and 14 days.
These two genes play a role in bone formation. Further implications of the gene deregulations described above will be discussed below. A Heatmaps represent expression profiles of transcripts significantly affected by rotenone treatment in the liver, heart left ventricle apex and brain stem over time.
Changes in gene expression are demonstrated by the color bar to the left of the diagram. Red represents increased and green represents decreased expression levels, indicated as ratios relative to the mean of the time-matched control group. B — M Tables show different affected pathways. Arrows represent the direction of deregulation of genes associated with the respective pathway. NDEG not found as deregulated by our selected cutoffs indicates that genes belonging to this pathway were not significantly deregulated in the specific organ and time point indicated.
Rotenone acts as a strong inhibitor of the mitochondrial complex I. The resulting incomplete electron transfer within the MRC leads to ATP depletion and in turn promotes the formation of ROS and thereby induces oxidative stress and apoptosis in cells 2 , 3. Moreover, rotenone can inhibit microtubule assembly through binding to tubulin leading to the inhibition of cell proliferation 7.
In oncology drug research mitochondrial metabolism has recently evolved as a target for cancer therapy, especially for tumors relying on oxidative metabolism 26 , with complex I suggested as one possible site of action. Since rotenone has also shown anti-carcinogenic activity in several studies 21 , 22 , 23 , 24 , the aim of the present study was to identify biomarker candidates and provide enhanced mechanistic insights into the molecular and cellular effects of complex I inhibitors after in vivo treatment, using rotenone as a tool compound.
Therefore rats were exposed to 0 or ppm rotenone through their diet up to 14 days and various parameters including gene expression profiling were examined. Three target organs, liver, bone marrow and bone, were identified through these investigations. Complex I inhibition by rotenone was confirmed in the liver through measurement of complex I activity in isolated mitochondria after 1, 3 and 14 days of treatment.
Gene expression analysis in liver revealed increased expression of mRNAs encoding proteins associated with mitochondrial genesis and the mitochondrial electron transport chain, especially of those encoding complex I subunits, after rotenone treatment.
This could be a feedback reaction to complex I inhibition by rotenone, likely leading to reduced mitochondrial energy supply.
It is proposed that this reduced supply was partially responsible for the weight loss within the first 2 days and the subsequent constant but not increasing body weight development observed during the 14 day treatment period. Additionally, in the liver, heart and brain stem a number of genes involved in oxidative stress responses were up-regulated.
This was potentially caused by an increase in the formation of ROS upon incomplete electron transfer due to the inhibition of complex I activity by rotenone, as previously described 4. In addition, expression of Hif1 target genes e. Lox lysyl oxidase and Loxl2 lysyl oxidase-like 2 and the gene Hyou1 Hypoxia up-regulated 1 , usually induced by hypoxia, was decreased.
Although activation of Hif1 in the context of hypoxia is suggested to be induced by mitochondrial ROS formation 34 , 35 , complex I inhibitors, including rotenone, have been known to inhibit the Hif1-pathway even under hypoxic conditions 26 , 36 , This might be explained by reduced O 2 consumption in mitochondria with an increase in cytosolic oxygen levels due to complex I inhibition and subsequent reduced electron transport chain activity.
This apparent reduced energy supply may also be responsible for other findings in liver. Histopathological investigations and direct glycogen measurements indicated early loss of liver glycogen within the first 3 days. Rotenone-treatment induced liver glycogen depletion was observed previously by others From these observations one may expect increased glycogenolysis leading to the release of glucose into the bloodstream, allowing energy generation through the glycolysis pathway.
However, gene expression analysis showed mostly decreased expression of genes encoding proteins participating in glycogenolysis. This could potentially be explained by a negative feedback reaction resulting from the earlier increased degradation of glycogen.
An exception to the mostly decreased expression of genes encoding glycogenolysis-associated proteins was an increased hepatic expression of the gene for GAA Lysosomal alpha-glucosidase. GAA is essential for the breakdown of glycogen to glucose in lysosomes, suggesting all available resources of glycogen were utilized. Lactate, which is a component in the glycogen-glucose metabolic network, was increased in the blood after rotenone administration.
Gene expression deregulation in this context indicated decreased expression of genes coding for proteins involved in the insulin pathway and for glycolytic enzymes in the liver and heart. Downregulation of glycolysis may be explained by feedback regulation to high blood lactate levels to avoid severe lactic acidosis. Blood glucose levels were only slightly reduced after two weeks of treatment presumably due to a tight regulation by the rat to maintain stable blood glucose levels.
Further, the rat is able to avoid hypoglycemia through the modulation of metabolic pathways that generate glucose from other resources including the breakdown of glycogen, proteins, and lipids. The latter is supported by the increased expression of genes encoding fatty acid oxidation enzymes in the liver and heart. The decreased expression levels of genes coding for proteins involved in cell proliferation and fatty acid synthesis at all time points in liver and heart, may potentially represent a response to reduced mitochondrial energy supply overall, to avoid not acutely required energy consuming processes.
This includes e. With respect to cholesterol biosynthesis, the expression of genes encoding the corresponding enzymes were decreased after 1 and 3 days, but then increased after 14 days of rotenone treatment.
However, genes encoding bile acid synthesis enzymes were increased at all time points analyzed. This may be explained by stimulated increased synthesis of bile acids required as emulsifiers for dietary lipids in the intestine, leading to decreased cholesterol levels, in turn activating cholesterol synthesis at the later time point.
Supporting evidence for this mRNA levels encoding Srebf2 Sterol regulatory element binding transcription factor 2 , the major regulator of cholesterol synthesis gene transcription, were increased at the 14 day time point. In addition, increased mRNA levels were also seen for the gene encoding the key enzyme of cholesterol biosynthesis Hmgcr 3-hydroxymethylglutaryl-CoA reductase , and others of this biosynthetic pathway. Depletion of the bone marrow as observed by histopathological analysis of the femur and sternum, started already after the first day of treatment, leading to marked atrophy after 2 weeks.
Furthermore, FACS investigations showed a decrease of red progenitor cells, myeloid and lymphoid cells especially after 14 days of treatment, confirming general bone marrow depletion.
Bone marrow atrophy was also observed after 13 weeks of oral rotenone administration of ppm up to ppm through the diet in the NTP technical report Further, rotenone treatment had distinct effects on erythropoiesis, leading to decreased extramedullary erythropoiesis in the spleen, as detected histopathologically. FACS-analysis indicated increased numbers of erythroid cells in femoral bone marrow with a shift towards more mature forms over time.
This shift to more mature erythroid stages in the bone marrow was paralleled in peripheral blood by an increase in red blood parameters Ery, Hb, Hct at the later time point, and a decrease of the number of reticulocytes, i.
In parallel to reduced numbers of reticulocytes, gene expression analysis showed decreased expression of genes encoding isoforms of the oxygen carrier hemoglobin in the heart and liver tissue. Further, decreased expression of genes involved in hematopoiesis mainly in the heart after 3 and 14 days, was observed. This likely reflects rotenone-induced processes in blood circulating through these organs. Together, these results suggest a significantly impaired generation of hematopoietic cells.
In general, hematopoietic tissue has a strong energy demand due to its high proliferative activity. Therefore mitochondrial complex I inhibition by rotenone leading to decreased energy supply could be a likely reason for bone marrow depletion. The additional inhibitory effect of rotenone on microtubule assembly 5 , 6 , 7 may also be involved in some of the observed effects, leading to mitotic arrest and inhibition of cell proliferation of these rapidly dividing cells.
Previously, diminished pyrimidine synthesis was discussed as a potential reason for ineffective hemopoiesis after rotenone treatment 40 with the resulting depletion of nucleotides leading to reduced cell division and proliferation. With respect to fish, trout and salmon are the most sensitive, sunfish are less sensitive and catfish are the most resistant. Fish, insects, birds and mammals have natural enzymes that will detoxify sub-lethal amounts of rotenone. Fish are highly susceptible because rotenone is readily absorbed through their gills, and they cannot escape exposure to it.
If biologists want to neutralize the effects of rotenone in lakes or rivers, potassium permanganate or chlorine can be used. These are added to the water at a ratio with the concentration of rotenone applied plus sufficient additional compound to satisfy the chemical oxidation demand caused by organic matter that may be present in the treated water.
The toxicity can be reversed by placing affected fish in a water solution of methylene blue. If fish are captured early during a treatment, they may also be revived by placing them in untreated water.
Success can be enhanced if the water is highly oxygenated or contains an oxidizing agent to detoxify any residual rotenone that may be on the gills or body surface. Rotenone is an unstable compound that breaks down when exposed to light, heat, oxygen and alkaline water.
The breakdown process is very rapid. Scientists have been able to identify about 20 degradation products, most of which spontaneously break down to lesser non toxic substances. Ultimately, rotenone breaks down into carbon dioxide and water; two common substances.
How fast rotenone breaks down is affected by temperature, light, oxygen and alkalinity. Generally, most treatments are made during summer months. As water cools, biological and chemical processes slow down and the breakdown of rotenone also slows.
Detoxification may take longer in acid waters, in very soft water, or in deep stratified bodies of water. Generally, most lakes treated with rotenone completely detoxify within five weeks of treatment. Rotenone is unstable and will degrade rapidly with exposure to light, heat, oxygen and alkaline water. In natural waters, other factors that influence the degradation rate and therefore reduce the toxic effect include the presence of organic debris, turbidity, lake shape and depth, dilution by inlets and runoff and the dosage used.
The presence of ice and snow cover may prolong the toxic effect. If desired or necessary, a treatment can be ended or toxicity can be removed by adding oxidizing chemicals, such as potassium permanganate or chlorine, to accelerate the natural breakdown of rotenone.
The mobility of rotenone in soil is low to slight. The expected leaching distance of rotenone in soils would be only two cm less than one inch in most types of soils. An exception would be in sandy soils where the expected leaching distance is about eight cm sightly more than three inches. Rotenone is strongly bound to organic matter in soil, so it is unlikely that it would enter ground water, even if it had not degraded.
Because of its rapid breakdown, rotenone leaves only temporary residues that would not persist as pollutants of ground water supplies. Fishery resource managers have tried many ways to manipulate fish populations.
Although some approaches are useful in special circumstances, most are only partially effective. Others take several years before the outcome is evident, and some apply only to one or two species. Use of a fish toxicant enables managers to establish a definite population at a specific time and makes it possible to clearly follow growth and abundance of the re-stocked species. Generally, the problem species are gizzard shad, carp, and bullheads.
These are fish that have very high reproduction rates and that are very tolerant of declining water quality. If predator populations are over fished, so many young of the problem species survive that they soon may represent over 90 percent of the fish present. When this occurs, the lake or stream becomes filled with small, stunted fish.
Gizzard shad cannot be caught on hook and line and they have no food or market value. Although some large carp and bullheads may be taken by anglers or commercial fishermen, they are generally not very popular species. The commercial value of these fish is also quite low. Commercial fishing will remove the largest fish but the space provided by their removal is usually filled by even more young carp, shad, or bullheads. It is usually diluted and applied through drip stations, or sprayers, or pumped through a hose into the propeller wash of a power boat.
Aerial applications are sometimes made. Rotenone persists for only a short time at high temperatures. Consequently, biologists usually try to treat during warm months when the waters will quickly detoxify and can be restocked at a time when hatchery raised fish are available. However, applications made in the fall and winter are also quite effective.
0コメント