Corticosteroid and thyroid responses of larval and juvenile turbot exposed to the water-soluble fraction of crude oil

Turbot larvae (24–590 degree C days; 2–32 days post-hatch) and juveniles (1345 degree C days; 98 days post-hatch), were exposed for 6 h to 25, 33 and 50% water-soluble fraction (WSF) of crude oil in either static or flow-through test systems. Larvae showed generalized primary endocrine responses, identified by elevated whole body cortisol content from as early as 2 days post-hatch. In older larvae and juveniles, the response was related to the WSF concentration. This dose-response relationship was not apparent in younger and yolk-sac larvae. Whole body thyroxine content of turbot larvae exposed to the WSF of crude oil was increased, but triiodothyronine content remained stable. Aromatic hydrocarbon concentrations [benzene, toluene, ethylbenzene and xylene (BTEX) and naphthalenes] remained constant during flow-through tests, but 65% of the initial level of BTEX hydrocarbons and 40% of the naphthalenes were lost during static exposures. Larval mortalities increased with exposure to an increasing concentration of crude oil WSF. Larval activity was significantly reduced even at the lowest WSF concentration.     

Bioenergetics of acclimation to permethrin (NRDC-143) by rainbow trout

Metabolic rates associated with sustained, prolonged and critical swimming speeds were examined in 10 g trout exposed to 5% 96 hr LC50 (0.75 microgram X l-1) and 10% 96 hr LC50 (1.50 micrograms X l-1) at 12 degrees C. Permethrin did not influence the metabolic cost for swimming at sustained and prolonged speeds. Basal metabolic rate increased on initial exposure to permethrin reaching maximum values after 7 days and declined to the control level after 13 days in 5% and after 32 days in 10% 96 hr LC50. Critical swimming speeds were adversely affected in a manner reflective of the effects of permethrin on basal metabolic rate. Elevation in basal metabolic rate in fish exposed to permethrin was a result of increased energy requirements due to physiological stress, detoxication and tissue repair.     

Endocrine, osmoregulatory, respiratory and haematological parameters in flounder exposed to the water soluble fraction of crude oil

Flounders Pleuronectes flesus with an implanted vascular catheter were exposed to a 50% dilution of the water soluble fraction (WSF) of Omani crude oil (c. 6ppm total aromatic hydrocarbons) and serial blood samples taken to determine their endocrine status (cortisol, catecholamines and thyroid hormones) and the resultant and/or causal physiological (haematological, ionoregulatory and respiratory) disturbances. This resulted in a progressive increase in plasma cortisol concentrations from 3 h onwards (rising from 18 to 51 ng ml⁻¹ after 48-h exposure), and increased plasma glucose concentrations indicating a generalized stress response. Plasma T3 and T4 concentrations of both control and WSF-exposed groups declined progressively over the experimental period; exposure to the WSF of crude oil further depressed plasma T4 concentrations but not plasma T₃ concentrations relative to those of control fish. Plasma osmolality and sodium and chloride concentrations were stable in WSF-exposed fish, however, plasma potassium concentrations were increased significantly at the 24-and 48-h sampling points. The most profound physiological disturbance in WSF-exposed fish was a dramatic decline in blood oxygen content (CvO₂) (from 2–8 to 0–8 ml 100 ml⁻¹ after 48-h exposure), which is likely to be the cause of the increased plasma noradrenaline concentrations from 3 h onwards. Increased noradrenaline is likely in turn to have been responsible for the significant increase in blood haematocrit and blood haemoglobin at the 3-h sampling point, although the dominant effect in the longer-term was a significant decline in both of these haematological parameters.     

Hydrocarbon contamination decreases mating success in a marine planktonic copepod

The mating behavior and the mating success of copepods rely on chemoreception to locate and track a sexual partner. However, the potential impact of the water-soluble fraction of hydrocarbons on these aspects of copepod reproduction has never been tested despite the widely acknowledged acute chemosensory abilities of copepods. I examined whether three concentrations of the water-soluble fraction of diesel oil (0.01%, 0.1% and 1%) impacts (i) the swimming behavior of both adult males and females of the widespread calanoid copepod Temora longcornis, and (ii) the ability of males to locate, track and mate with females. The three concentrations of the water-soluble fraction of diesel oil (WSF) significantly and non-significantly affect female and male swimming velocities, respectively. In contrast, both the complexity of male and female swimming paths significantly decreased with increasing WSF concentrations, hence suggesting a sex-specific sensitivity to WSF contaminated seawater. In addition, the three WSF concentrations impacted both T. longicornis mating behavior and mating success. Specifically, the ability of males to detect female pheromone trails, to accurately follow trails and to successfully track a female significantly decreased with increasing WSF concentrations. This led to a significant decrease in contact and capture rates from control to WSF contaminated seawater. These results indicate that hydrocarbon contamination of seawater decreases the ability of male copepods to detect and track a female, hence suggest an overall impact on population fitness and dynamics.     

Daily rhythms of toxicity and effectiveness of anesthetics (MS222 and eugenol) in zebrafish (Danio rerio)

Although the chronotoxicity of xenobiotics is relatively well known in mammals, the existence of daily rhythms of drug toxicity and effectiveness in fish has been neglected to date. The aim of this research was to investigate the influence of the time (middle of the light phase [ML] versus middle of the dark phase [MD]) of exposure to two anesthetic substances (MS-222 or clove oil) commonly used with fish on the median lethal concentration (LC(50)) and swimming activity of zebrafish (Danio rerio). To this end, adult zebrafish were kept under a 12 h:12 h light-dark (LD) cycle and exposed to different concentrations of the anesthetics for 15 min at ML or MD. LC(50) calculations were performed using the Spearman-Karber program, whereas swimming activity was video-recorded and analyzed with specialized software. Zebrafish exhibited a mostly diurnal activity pattern (77.9% of activity occurring during daytime). The acute toxicity and mortality caused by MS-222 and eugenol varied with the time of exposure. For MS-222, the LC(50) was 170.6 ± 7.4 mg/L in fish exposed at ML and 215.6 ± 3.9 mg/L at MD, whereas for eugenol the LC(50) was 70.3 ± 3.1 mg/L at ML and 104.9 ± 5.4 mg/L at MD. Exposure to sublethal concentrations of MS-222 and eugenol altered the swimming patterns of zebrafish in a different manner depending on the time of exposure. Thus, the time required for decreasing swimming activity during exposure to anesthetics was shorter at ML than at MD, whereas the recovery period was longer during the day. In conclusion, these results revealed that the toxicity and effectiveness of both anesthetic substances is highest during daytime, the active phase of fish, thus suggesting a link between the daily rhythms of behavior and toxicity.     

Ion homeostasis and interrenal stress responses in juvenile Pacific herring, Clupea pallasi, exposed to the water-soluble fraction of crude oil

Juvenile Pacific herring, Clupea pallasi, were exposed both acutely (96 h) and chronically (9 weeks) to three concentrations of the water-soluble fraction (WSF) of North Slope crude oil. Mean (± S.E.) total PAH (TPAH) concentrations at the beginning of the acute exposure experiment were: 9.7 ± 6.5, 37.9 ± 8.6 and 99.3 ± 5.6 μg/L. TPAH concentrations declined with time and the composition of the WSF shifted toward larger and more substituted PAHs. Significant induction of hepatic cytochrome P450 content, ethoxyresorufin O-deethylase and glutathione-S-transferase activities in WSF-exposed fish indicated that hydrocarbons were biologically available to herring. Significant but temporary, elevations in plasma cortisol (4.9-fold and 8.5-fold increase over controls in the 40 and 100 μg/L groups, respectively), lactate (2.2-fold and 3.1-fold over controls in the 40 and 100 μg/L groups) and glucose (1.3-fold, 1.4-fold and 1.6-fold over controls in the 10, 40 and 100 μg/L groups) occurred in fish exposed acutely to WSF. All values returned to baseline levels by 96 h. Similar responses were seen with the first of several sequential WSF pulses in the chronic exposure study. Subsequent WSF pulses resulted in muted cortisol responses and fewer significant elevations in both plasma lactate and glucose concentrations. Hematocrit, leucocrit, hemoglobin concentration and liver glycogen content were not affected by acute or chronic WSF exposure. Plasma [Cl⁻], [Na⁺] and [K⁺] were significantly higher in the 100 μg/L WSF-exposed group by 96 h compared to control fish, and continued to be elevated through the entire chronic exposure period. Unlike the measured stress parameters, ionoregulatory dysfunction was not modulated by WSF pulses. The results of this study suggest that chronic exposure to WSF affects at least two important physiological systems in herring: the ability of fish to maintain ion homeostasis and the interrenally-mediated organismal stress response.     

Acute toxicity of the water-soluble fraction of spent lubricating oil on the African catfish Clarias gariepinus

Static tests were employed to assess the acute toxicity of the water-soluble fraction (WSF) of spent automotive lubricating oil (of mixed SAE grades) on Clarias gariepinus, a freshwater fish commonly cultured in Nigeria. Median lethal concentrations (LC50) of the WSF were found to decrease as a function of exposure time from 690+/-21 (after 24 h) to 513+/-58 mg/l (after 96 h). The characteristics of the WSF such as mean acidity (pH 6.6), turbidity (40 NTU), total dissolved solids (TDS; 40 mg/l) and significantly reduced (P<0.05) dissolved-oxygen (DO) values (1.44 mg/l) were not compliant with existing standards set for discharged effluents. The solubility of the detected straight-chain aliphatics ranked as C14>C16>C32>C18>C28; that of the simple aromatics was ortho-xylene>para-xylene; and that of the polyaromatic hydrocarbons (PAHs) was acenaphthylene>9H-fluorene>naphthalene>anthracene>phenanthrene>chrysene>benzo[k]fluoranthene>benzo[a]pyrene>benzo[b]fluoranthene, most of which being serious carcinogens. These oil constituents and the overall physico-chemical properties of the WSF are expected to act synergistically on the test organism (C. gariepinus), eliciting the quantal responses observed. The toxicity of the WSF points to the base constituent, oxidative degradation, and mechano-chemical reactions associated with aged crankcase oils. These oils, therefore, should definitely no longer be disposed into water streams or landscape, not even at sub-lethal concentrations, because of the inherent toxicity of their soluble fractions and the associated danger of bioaccumulation.     

Influence of some environmental variables on the ascorbic acid status of striped mullet, Mugil cephalus Linn., tissues. III. Effects of exposure to oil

Exposure to water-soluble fractions (WSF) of a crude and two fuel oils altered the ascorbic acid (AsA) content of several striped mullet, Mugil cephalus , tissues. Exposure to sublethal concentrations of all three WSFs caused a depletion of AsA reserves in brain, gill, kidney and liver tissues, but not in muscle. There was a marked decline in AsA stores in kidney and gill tissues after only one day of exposure to WSFs of both crude and fuel oils. Liver AsA concentrations were significantly depleted after one week of oil exposure. Brain AsA content was only significantly depleted during chronic exposure to the highest oil concentration (20% WSF). A dose-dependent depletion of AsA reserves in the liver but not in the other tissues was observed one week after a single exposure to 2–20% WSFs of a No. 2 fuel oil. Exposure to 20% WSF of the No. 2 fuel oil caused a 47% decrease in liver AsA content one week later. Hepatic concentrations were still significantly depleted after 15 days, but had returned to control levels 20 days after the initial exposure. The data suggest that the depletion of tissue AsA reserves in fish inhabiting oil-contaminated environments could be sufficient on occasions to lead to AsA deficiency.     

Changes in selected blood component concentrations of rainbow trout, Salmo gairdneri Richardson, exposed to hypoxia or sublethal concentrations of phenol or ammonia

Rainbow trout were exposed to sublethal phenol or non-ionized ammonia concentrations or to hypoxia. Blood samples were taken after various exposure periods and the packed cell volume (PCV) value, the whole blood glucose concentration and the plasma cortisol and chloride ion concentrations measured. At low pollutant concentrations there were no significant changes in the blood components compared to control fish values. At higher concentrations the general response to the stressors was significant increases in the PCV value and the glucose and cortisol concentrations during the first few hours of exposure, followed by a gradual return to normal values in the subsequent exposure time. The increases in glucose and cortisol concentrations were approximately proportional to the pollutant concentrations no such correlation was found for the PCV values. No clear pattern of plasma chloride ion changes was found in any experiment. Levels of no acute effect, in terms of toxic units (TU) based on the pollutants' 48 h LC₅₀ values, were estimated for phenol as 0.3 TU and for un-ionized ammonia as 0.1 TU, using the plasma cortisol concentration measurements. The use of fish blood component measurements as general indicators of a stress response is discussed.     

Cortisol influences the antipredator behavior induced by chemical alarm cues in the Frillfin goby

We evaluated the effect of increased plasma cortisol levels on fish antipredator behavior induced by conspecific chemical alarm cues. The experimental model for the study was the Frillfin goby Bathygobius soporator. We first confirmed that the alarm substance induces typical defensive antipredator responses in Frillfin gobies and described their alarm substance cells (epidermal ‘club’ cells). Second, we confirmed that intraperitoneal cortisol implants increase plasma cortisol levels in this species. We then demonstrated that exogenous cortisol administration and subsequent exposure to an alarm substance decreased swimming activity to a greater extent than the activity prompted by either stimulus alone. In addition, cortisol did not abolish the sheltering response to the alarm chemical cue even though it decreased activity. As predators use prey movements to guide their first contact with the prey, a factor that decreases swimming activity clearly increases the probability of survival. Consequently, this observation indicates that cortisol helps improve the antipredator response in fish.     

Cortisol response to acute stress in jundiá Rhamdia quelen acutely exposed to sub-lethal concentrations of agrichemicals

Exposure to agrichemicals can have deleterious effects on fish, such as disruption of the hypothalamus-pituitary-inter-renal axis (HPI) that could impair the ability of fish to respond to stressors. In this study, fingerlings of the teleost jundiá (Rhamdia quelen) were used to investigate the effects of the commonly used agrichemicals on the fish response to stress. Five common agrichemicals were tested: the fungicide - tebuconazole, the insecticide - methyl-parathion, and the herbicides - atrazine, atrazine+simazine, and glyphosate. Control fishes were not exposed to agrichemicals and standard stressors. In treatments 2-4, the fishes were exposed to sub-lethal concentrations (16.6%, 33.3%, and 50% of the LC(50)) of each agrichemical for 96 h, and at the end of this period, were subjected to an acute stress-handling stimulus by chasing them with a pen net. In treatments 5-7 (16.6%, 33.3%, and 50% of the LC(50)), the fishes were exposed to the same concentrations of the agrichemicals without stress stimulus. Treatment 8 consisted of jundiás not exposed to agrichemicals, but was subjected to an acute stress-handling stimulus. Jundiás exposed to methyl-parathion, atrazine+simazine, and glyphosate presented a decreased capacity in exhibiting an adequate response to cope with stress and in maintaining the homeostasis, with cortisol level lower than that in the control fish (P<0.01). In conclusion, the results of this study clearly demonstrate that the acute exposure to sub-lethal concentrations of methyl-parathion, atrazine+simazine, and glyphosate exert a deleterious effect on the cortisol response to an additional acute stressor in the jundiá fingerlings.     

Stenotherms at sub-zero temperatures: thermal dependence of swimming performance in Antarctic fish

We examined the burst swimming performance of two Antarctic fishes, Trematomus bernacchii and T. centronotus, at five temperatures between -1 degrees C and 10 degrees C. As Antarctic fishes are considered one of the most cold specialised and stenothermal of all ectotherms, we predicted they would possess a narrow thermal performance breadth for burst swimming and a correlative decrease in performance at high temperatures. Burst swimming was assessed by videotaping swimming sequences with a 50-Hz video camera and analysing the sequences frame-by-frame to determine maximum velocity, the distance moved throughout the initial 200 ms, and the time taken to reach maximum velocity. In contrast to our prediction, we found both species possessed a wide thermal performance breadth for burst swimming. Although maximum swimming velocity for both T. bernacchii and T. centronotus was significantly highest at 6 degrees C, maximum velocity at all other test temperatures was less than 20% lower. Thus, it appears that specialisation to a highly stable and cold environment is not necessarily associated with a narrow thermal performance breadth for burst swimming in Antarctic fish. We also examined the ability of the Antarctic fish Pagothenia borchgrevinki to acclimate their burst-swimming performance to different temperatures. We exposed P. borchgrevinki to either -1 degrees C or 4 degrees C for 4 weeks and tested their burst-swimming performance at four temperatures between -1 degrees C and 10 degrees C. Burst-swimming performance of Pagothenia borchgrevinki was unaffected by exposure to either -1 degrees C or 4 degrees C for 4 weeks. Maximum swimming velocity of both acclimation groups was thermally independent over the total temperature range of 1 degrees C to 10 degrees C. Therefore, the loss of any capacity to restructure the phenotype and an inability to thermally acclimate swimming performance appears to be associated with inhabiting a highly stable thermal environment.     

The effects of stress induced by cortisol administration on the repeatability of swimming performance tests in the European sea bass (Dicentrarchus labrax L.)

The impact of stress induced by cortisol administration on the swimming performance of the European sea bass was tested measuring the fish recovery capability using a respirometer. The recovery test consisted of two exhaustive swimming exercises (U _crit) separated by a recovery period. Thirty-eight fish were subjected to this trial preceded or not (control group) by a cortisol (cortisol group) or saline (placebo) injection. For validation, the classical stress parameters (cortisol, glucose, lysozyme, Hct, Hb and RBCC) were monitored. During the recovery tests, only the cortisol group showed a significant reduction in the recovery capability that was interpreted as a sign of possible physiological impairment. Hct, Hb and RBCC did not show significant inter and intra-group differences, while cortisol and glucose increased as a response to fatigue in all the groups at the end of the trials. No immune (lysozyme) response was observed in control and placebo groups, while a reduction was evidenced in the cortisol group.     

The interactive effects of exercise and gill remodeling in goldfish (Carassius auratus)

Gill remodeling in goldfish (Carassius auratus) is accomplished by the appearance or retraction of a mass of cells (termed the interlamellar cell mass or ILCM) between adjacent lamellae. Given the presumed effects of gill remodeling on diffusing capacity, the goals of the current study were (1) to determine the consequences of increased aerobic O(2) demand (swimming) on gill remodelling and (2) to assess the consequences of the presence or absence of the ILCM on aerobic swimming capacity. Fish acclimated to 7?°C exhibited a marked increase in the ILCM which occupied, on average, 70.0?±?4.1?% of the total interlamellar channel area in comparison to an average ILCM area of only 28.3?±?0.9?% in fish acclimated to 25?°C. Incrementally increasing swimming velocity in fish at 7?°C to achieve a maximum aerobic swimming speed (U (CRIT)) within approximately 3?h resulted in a marked loss of the ILCM area to 44.8?±?3.5?%. Fish acclimated to 7?°C were subjected to 35?min swimming trials at 30, 60 or 80?% U (CRIT) revealing that significant loss of the ILCM occurred at swimming speeds exceeding 60?% U (CRIT). Prior exposure of cold water-acclimated fish to hypoxia to induce shedding of the ILCM did not affect swimming performance when assessed under normoxic conditions (control fish U (CRIT)?=?2.34?±?0.30 body lengths s(-1); previously hypoxic fish U (CRIT)?=?2.99?±?0.14 body lengths s(-1)) or the capacity to raise rates of O(2) consumption with increasing swimming speeds. Because shedding of ILCM during U (CRIT) trials complicated the interpretation of experiments designed to evaluate the impact of the ILCM on swimming performance, additional experiments using a more rapid 'ramp' protocol were performed to generate swimming scores. Neither prior hypoxia exposure nor a previous swim to U (CRIT) (both protocols are known to cause loss of the ILCM) affected swimming scores (the total distance swum during ramp U (CRIT) trials). However, partitioning all data based on the extent of ILCM coverage upon cessation of the swimming trial revealed that fish with less than 40?% ILCM coverage exhibited a significantly greater swimming score (539?±?86?m) than fish with greater than 50?% ILCM coverage (285?±?70?m). Thus, while loss of the ILCM at swimming speeds exceeding 60?% U (CRIT) confounds the interpretation of experiments designed to assess the impact of the ILCM on swimming performance, we suggest that the shedding of the ILCM, in itself, coupled with improved swimming scores in fish exhibiting low ILCM coverage (<40?%), provide evidence that the ILCM in goldfish acclimated to cold water (7?°C) is indeed an impediment to aerobic swimming capacity.     

A note on pre-spawning maternal cortisol exposure in farmed Atlantic salmon and its impact on the behaviour of offspring in response to a novel environment

This study was designed to assess whether pre-spawning maternal cortisol administration and an additional stressor, here modelled by mild hyperthermia experienced during incubation, affected the behavioural responses of farmed Atlantic salmon (Salmo salar) offspring when exposed to a novel environment. Mature females were injected prior to stripping with 0, 50 or 100 mg/kg cortisol. After fertilization the eggs were kept at incubation temperatures of either 8 or 10 °C. Four months after hatching, the fish were introduced to a novel environment, i.e. an aquarium (38 l). In each trial two individuals originating from different exposure groups were video recorded and their activity (number of turns, time spent not swimming, time spent at the bottom) and feeding behaviour were measured. Maternal cortisol increased time spent non-swimming and also time spent at the bottom, while cortisol and temperature together additionally affected number of turns. To the best of our knowledge this study is the first in fish to demonstrate a possible link between the maternal endocrinological state at spawning and the offspring's behavioural reactivity to novel situations.     

Exposure of Goldfish (Carassius auratus) to Bluegills (Lepomis macrochirus) Enhances Expression of Stress Protein 70 mRNA in the Brains and Increases Plasma Cortisol Levels

The effect of psychological stress on HSP70 mRNA in the brains and plasma cortisol levels in goldfish was examined. Stress was induced by exposure to a predator (bluegills). HSP70 mRNA and cortisol were determined by Northern blotting and ELISA, respectively. Goldfish exposed to four predators in the same tank without a partition showed marked increases in HSP70 mRNA and cortisol levels 6 hr and 12 hr after commencement of exposure. When goldfish were separated from bluegills with a net partition, HSP70 mRNA expression was enhanced after 6 hr, and returned to the control level after 12 hr. Plasma cortisol levels increased after 2 hr, and returned to the control level after 6 hr. When goldfish were placed in a transparent tank around which bluegills were swimming, HSP70 mRNA expression and cortisol levels increased after 6 hr and 12 hr. Goldfish exposed to water circulating through a tank with bluegills showed no sign of changes in HSP70 mRNA expression or cortisol levels. These results suggest that psychological stress enhanced HSP70 mRNA expression in the brains and increased plasma cortisol levels via visual perception.     

Effect of crude oil petroleum hydrocarbons on protein expression of the prawn Macrobrachium borellii

Hydrocarbon pollution is a major environmental threat to ecosystems in marine and freshwater environments, but its toxicological effect on aquatic organisms remains little studied. A proteomic approach was used to analyze the effect of a freshwater oil spill on the prawn Macrobrachium borellii. To this aim, proteins were extracted from midgut gland (hepatopancreas) of male and female prawns exposed 7 days to a sublethal concentration (0.6 ppm) of water-soluble fraction of crude oil (WSF). Exposure to WSF induced responses at the protein expression level. Two-dimensional gel electrophoresis (2-DE) revealed 10 protein spots that were differentially expressed by WSF exposure. Seven proteins were identified using MS/MS and de novo sequencing. Nm23 oncoprotein, arginine methyltransferase, fatty aldehyde dehydrogenase and glutathione S-transferase were down-regulated, whereas two glyceraldehyde-3-phosphate dehydrogenase isoforms and a lipocalin-like crustacyanin (CTC) were up-regulated after WSF exposure. CTC mRNA levels were further analyzed by quantitative real-time PCR showing an increased expression after WSF exposure. The proteins identified are involved in carbohydrate and amino acid metabolism, detoxification, transport of hydrophobic molecules and cellular homeostasis among others. These results provide evidence for better understanding the toxic mechanisms of hydrocarbons. Moreover, some of these differentially expressed proteins would be employed as potential novel biomarkers.     

Temperature effects on metabolic rate, swimming performance and condition of Pacific cod Gadus macrocephalus Tilesius

Critical swimming speed ( U _crit) and rate of oxygen consumption of Pacific cod Gadus macrocephalus acclimated to 4 and 11° C were determined to assess the influence of water temperature on performance. The physiological effect of exercise trials on fish held at two temperatures was also assessed by comparing haematocrit and plasma concentrations of cortisol, metabolites and ions collected from fish before and after testing. The U _crit of fish acclimated and exercised at 4° C did not differ from those acclimated and exercised at 11° C [1·07 body lengths (total length) s⁻¹]. While the standard metabolic rate of 11° C acclimated fish was 28% higher than that of 4° C fish, no significant difference was observed between fish acclimated at the two temperatures. Plasma concentrations of cortisol, glucose and lactate increased significantly from pre- to post-swim in both groups, yet only concentrations of cortisol differed significantly between temperature treatments. Higher concentrations of cortisol in association with greater osmoregulatory disturbance in animals acclimated at the lower temperature indicate that the lower water temperature acted as an environmental stressor. Lack of significant differences in U _crit between temperature treatments, however, suggests that Pacific cod have robust physiological resilience with respect to swimming performance within temperature changes from 4 to 11° C.     

Acute exposure to 2,4-dinitrophenol alters zebrafish swimming performance and whole body triglyceride levels

While swimming endurance (critical swimming speed or U(crit)) and lipid stores have both been reported to acutely decrease after exposure to a variety of toxicants, the relationship between these endpoints has not been clearly established. In order to examine these relationships, adult zebrafish (Danio rerio) were aqueously exposed to solvent control (ethanol) or two nominal concentrations of 2,4-dinitrophenol (DNP), a mitochondrial electron transport chain uncoupler, for a 24-h period. Following exposure, fish were placed in a swim tunnel in clean water for swimming testing or euthanized immediately without testing, followed by analysis of whole body triglyceride levels. U(crit) decreased in both the 6 mg/L and 12 mg/L DNP groups, with 12 mg/L approaching the LC??. A decrease in tail beat frequency was observed without a significant change in tail beat amplitude. In contrast, triglyceride levels were elevated in a concentration-dependent manner in the DNP exposure groups, but only in fish subjected to swimming tests. This increase in triglyceride stores may be due to a direct interference of DNP on lipid catabolism as well as increased triglyceride production when zebrafish were subjected to the co-stressors of swimming and toxicant exposure. Future studies should be directed at determining how acute DNP exposure combines with swimming to cause alterations in triglyceride accumulation.     

Hepatic aryl hydrocarbon hydroxylase activities in coho salmon (Oncorhynchus kisutch) exposed to petroleum hydrocarbons

Coho salmon exposed to the water soluble fraction (WSF) of Cook Inlet crude oil for a maximum of 30 days showed a greater than three-fold increase in hepatic aryl hydrocarbon hydroxylase activity. The initial increase in enzyme activity appeared between 2 and 5 days of exposure and increased as a function of increased exposure time. Persistence of the induced enzyme activity was dependent on the length and the concentration of WSF exposure. Handling stress had no effect on the AHH activity, but starvation caused a decrease in the activity.