Oana Birceanu

Modes of metal toxicity and impaired branchial ionoregulation in rainbow trout exposed to mixtures of Pb and Cd in soft water.

Models such as the Biotic Ligand Model (BLM) predict how natural organic matter (NOM) and competing ions (e.g., Ca(2+), H(+) and Na(+)) affect metal bioavailability and toxicity in aquatic organisms. However, such models focus upon individual metals, not metal mixtures. This study determined whether Pb and Cd interact at the gill of rainbow trout (Oncorhynchus mykiss) when trout were exposed to environmentally relevant concentrations of these metals (Cd<100 nmol L(-1); Pb<500 nmol L(-1)) in soft (<100 micromol Ca(2+)L(-1)), moderately acidic (pH 6.0) water. The 96-h LC50 for Pb was 482 nmol L(-1), indicating that Pb was one-order of magnitude more toxic in soft, acidic water than in harder, circumneutral pH waters. The LC50 for Cd alone was also low, 6.7 nmol L(-1). Surprisingly, fish acclimated to soft water had multiple populations of Pb-gill and Cd-gill binding sites. A low capacity, high affinity population of Pb-gill binding sites had a B(max) of 18.2 nmol g(-1) wet weight (ww) and apparent K(Pb-gill)=7.05, but a second low affinity population could not be saturated up to free Pb concentrations approaching 4000 nmol L(-1). Two populations of Cd-gill binding sites were characterized: a high affinity, low capacity population with an apparent K(Cd-gill)=7.33 and B(max)=1.73 nmol g(-1) ww, and a low affinity, high capacity population with an apparent K(Cd-gill)=5.86, and B(max)=13.7 nmol g(-1) ww. At low concentrations, Cd plus Pb accumulation was less than additive because Cd out-competed Pb for gill binding sites, which were likely apical Ca(2+)-channels. While disturbances to Ca(2+) influx were caused by Cd alone, Pb alone had no effect. However, Pb exacerbated Cd-induced disturbances to Ca(2+) influx demonstrating that, although Pb- plus Cd-gill binding was less than additive due to competition, the effects (ionic disturbances) were more than additive (synergistic). Pb was also likely binding to intracellular targets, such as branchial carbonic anhydrase, which led to inhibited Na(+) influx. This ionic disturbance was exacerbated by Cd. We conclude that exposure to environmentally relevant concentrations of Pb plus Cd results in less than additive metal-gill binding in soft, moderately acidic waters. However, ionic disturbances caused by Cd plus Pb are greater than additive, and this may ultimately increase the toxicity of Cd-Pb mixtures to fishes. Our findings suggest that it may be necessary to re-evaluate water quality criteria and assumptions of the BLM for fish exposed to mixtures of Pb and Cd in the acidic, soft waters found in the Canadian Shield, Scandinavia and other sensitive regions.

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

The toxicity of 3-trifluoromethyl-4-nitrophenol (TFM) appears to be due to a mismatch between ATP supply and demand in lamprey, depleting glycogen stores and starving the nervous system of ATP. The cause of this TFM-induced ATP deficit is unclear. One possibility is that TFM uncouples mitochondrial oxidative phosphorylation, thus impairing ATP production. To test this hypothesis, mitochondria were isolated from the livers of sea lamprey and rainbow trout, and O(2) consumption rates were measured in the presence of TFM or 2,4-dinitrophenol (2,4-DNP), a known uncoupler of oxidative phosphorylation. TFM and 2,4-DNP markedly increased State IV respiration in a dose-dependent fashion, but had no effect on State III respiration, which is consistent with uncoupling of oxidative phosphorylation. To determine how TFM uncoupled oxidative phosphorylation, the mitochondrial transmembrane potential (TMP) was recorded using the mitochondria-specific dye rhodamine 123. Mitochondrial TMP decreased by 22% in sea lamprey, and by 28% in trout following treatment with 50μmolL(-1) TFM. These findings suggest that TFM acted as a protonophore, dissipating the proton motive force needed to drive ATP synthesis. We conclude that the mode of TFM toxicity in sea lamprey and rainbow trout is via uncoupling of oxidative phosphorylation, leading to impaired ATP production.

Failure of ATP supply to match ATP demand: The mechanism of toxicity of the lampricide, 3-trifluoromethyl-4-nitrophenol (TFM), used to control sea lamprey (Petromyzon marinus) populations in the Great Lakes

Although the pesticide, 3-trifluoromethyl-4-nitrophenol (TFM), has been extensively used to control invasive sea lamprey (Petromyzon marinus) populations in the Great Lakes, it is surprising that its mechanism(s) of toxicity is unresolved. A better knowledge of the mode of toxicity of this pesticide is needed for predicting and improving the effectiveness of TFM treatments on lamprey, and for risk assessments regarding potential adverse effects on invertebrate and vertebrate non-target organisms. We investigated two hypotheses of TFM toxicity in larval sea lamprey. The first was that TFM interferes with oxidative ATP production by mitochondria, causing rapid depletion of energy stores in vital, metabolically active tissues such as the liver and brain. The second was that TFM toxicity resulted from disruption of gill-ion uptake, adversely affecting ion homeostasis. Exposure of larval sea lamprey to 4.6 m gl(-1) TFM (12-h LC50) caused glycogen concentrations in the brain to decrease by 80% after 12h, suggesting that the animals increased their reliance on glycolysis to generate ATP due to a shortfall in ATP supply. This conclusion was reinforced by a 9-fold increase in brain lactate concentration, a 30% decrease in brain ATP concentration, and an 80% decrease in phosphocreatine (PCr) concentration after 9 and 12h. A more pronounced trend was noted in the liver, where glycogen decreased by 85% and ATP was no longer detected after 9 and 12h. TFM led to marginal changes in whole body Na(+), Cl(-), Ca(2+) and K(+), as well as in plasma Na(+) and Cl(-), which were unlikely to have contributed to toxicity. TFM had no adverse effect on Na(+) uptake rates or gill Na(+)/K(+)-ATPase activity. We conclude that TFM toxicity in the sea lamprey is due to a mismatch between ATP consumption and ATP production rates, leading to a depletion of glycogen in the liver and brain, which ultimately leads to neural arrest and death.

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.

Life stage dependent responses to the lampricide, 3-trifluoromethyl-4-nitrophenol (TFM), provide insight into glucose homeostasis and metabolism in the sea lamprey (Petromyzon marinus).

The primary method of sea lamprey (Petromyzon marinus) control in the Great Lakes is the treatment of streams and rivers with the pesticide 3-trifluoromethyl-4-nitrophenol (TFM), which targets larval sea lamprey. However, less is known about the effects of TFM on other stages of the sea lampreys complex life cycle. The goal of this study was to determine how TFM affected internal energy stores, metabolites, and ion balance in larval, juvenile (parasitic) and adult sea lamprey. The larvae were more tolerant to TFM than the adults, with a 2-fold higher 12h TFM LC50 and a 1.5-fold higher LC99.9. Acute (3h) exposure of the larvae, parasites and adults to their respective 12h TFM LC99.9 led to marked reductions in glycogen and phosphocreatine in the adult brain, with lesser or no effect in the larvae and parasites. Increased lactate in the brain, at less than the expected stoichiometry, suggested that it was exported to the blood. Kidney glycogen declined after TFM exposure, suggesting that this organ plays an important role in glucose homeostasis. TFM-induced disturbances to ion balance were minimal. In conclusion, TFM perturbs energy metabolism in all major stages of the sea lamprey life cycle in a similar fashion, but the adults appear to be the most sensitive. Thus, the adult stage could be a viable and effective target for TFM treatment, particularly when used in combination with other existing and emerging strategies of sea lamprey control.

Invasive crab eats through its gills

![Graphic][1] The green shore crab, Carcinus maenas , known by many as an invasive species that can be found just about anywhere in the world, lives in the ever-changing environment of the estuaries. This common arthropod is able to tolerate changes in water salinity, fluctuations in water

Waste recycling by gut symbionts

![Graphic][1] Hibernators, or animals that ‘sleep’ through the winter to conserve energy, have always fascinated scientists. To date, researchers have studied the adaptations that allow these animals to be inactive for so long and their ability to come back from their slumber at the

Mitochondria are too hot to handle

![Graphic][1] Back in 1957, in his article published in Scientific American (volume 197, pp. 131–144), biologist Philip Siekevitz called the mitochondrion the ‘powerhouse of the cell’, a term very much used today when we talk about this complex organelle. Mitochondria are organelles

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.

To be or not to be … male or female?

![Graphic][1] Whether one is genetically born as male or female is decided when the sperm meets the egg. It is only under unique conditions that Mother Nature would divert from such a rule in mammals. This is not the case in fish, where the environment can influence the sex that an animal