Changes in selected haematological parameters in juvenile chinook salmon subjected to a bacterial challenge and a toxicant

An infection and a toxicant were presented singly and in combination to juvenile chinook salmon. The fish were challenged with Renibacterium salmoniarum and exposed to two levels (0.05 and 0.50 × 96 h LC50) of the toxicant sodium pentachlorophenate. The experiment comprised measurement of seven blood parameters and observations on mortality and behaviour at 4-day intervals over a period of 40 days.
All fish receiving the combined treatment of bacterial challenge and higher level of toxicant died 12 days post-infection on the 8th day of toxicant exposure. Mortalities also occurred in the groups of diseased fish and fish receiving the toxicant alone. There were no mortalities in the appropriate control groups of unchallenged fish in clean water.
Most of the haematological changes pointed to a general haemodilution probably arising from progressive damage to the kidney and haematopoietic tissue by bacteria but which did not appear to be greatly affected by combined exposure to the toxicant. The blood parameters of the fish in clean water as well as those exposed to just the toxicant remained relatively constant. Higher mortality and sustained lower values of haematocrit, haemoglobin and glucose concentrations as well as red blood cell counts were present in both the diseased group of fish held in clean water and the disease plus low level toxicant group compared to the control fish; white blood cell counts were low initially but increased markedly as the infection progressed. This latter treatment combination also produced lower total protein and blood urea nitrogen concentrations.     

Mortality from duck plague virus in immunosuppressed adult mallard ducks

Environmental contaminants contain chemicals that, if ingested, could affect the immunological status of wild birds, and in particular, their resistance to infectious disease. Immunosuppression caused by environmental contaminants, could have a major impact on waterfowl populations, resulting in increased susceptibility to contagious disease agents. Duck plague virus has caused repeated outbreaks in waterfowl resulting in mortality. In this study, several doses of cyclophosphamide (CY), a known immunosuppressant, were administered to adult mallards (Anas platyrhynchos) to determine if a resultant decrease in resistance to a normally sub-lethal strain of duck plague virus would occur, and induce mortality in these birds. Death occurred in birds given CY only, and in birds given virus and CY, but not in those given virus only. There was significantly greater mortality and more rapid deaths in the duck plague virus-infected groups than in groups receiving only the immunosuppressant. A positively correlated dose-response effect was observed with CY mortalities, irrespective of virus exposure. A fuel oil and a crude oil, common environmental contaminants with immunosuppressive capabilities, were tested to determine if they could produce an effect similar to that of CY. Following 28 days of oral oil administration, the birds were challenged with a sub-lethal dose of duck plague virus. No alteration in resistance to the virus (as measured by mortality) was observed, except in the positive CY control group.     

Neonatally-induced thermotolerance: physiological responses

1. Broiler cockerels exposed to neonatal heat (35-37.8 degrees C for 24 hr) at 5 days of age experienced significantly lower mortality upon exposure to elevated temperatures (35-37.8 degrees C) at 43 days of age than did cockerels not given neonatal heat exposure. 2. No differences were found between neonatally stressed and neonatal control groups in water consumption, core and surface temperature, plasma T3 and T4, protein or glucose concentration when exposed to juvenile heat stress. 3. Heterophil to lymphocyte ratios were significantly lower in the neonatally stressed than in the neonatal control group when exposed to heat at 44 days of age. 4. The results indicate that lower mortality during periods of high environmental temperature in the neonatally stressed chicks may involve homeostatic mechanisms different from those utilized during acclimation to high environmental temperature.     

Impact of PCB on resistance to Flavobacterium psychrophilum after experimental infection of rainbow trout Oncorhynchus mykiss eggs by nanoinjection

The effects of sublethal exposure of a commercial blend of polychlorinated biphenyls (PCB), i.e. Clophen A50, on disease resistance to the aetiological agent of rainbow trout fry syndrome, Flavobacterium psychrophilum, were investigated. Newly fertilised rainbow trout Oncorhynchus mykiss eggs were nanoinjected with 2 doses of Clophen A50 (0.4 or 2 microg egg(-1)) and/or 100 colony forming units of F. psychrophilum. The mean cumulative mortality in control groups, and groups exposed to the lower dose of Clophen A50 (0.4 microg egg(-1)) was below 5.0%. The mean cumulative mortality in groups exposed to the higher dose of Clophen A50 (2.0 microg egg(-1)) was 5.8%, which was not significantly different from the control groups. In all groups infected with F. psychrophilum, with or without exposure to Clophen A50, significantly higher cumulative mortalities compared with control groups were recorded. No differences in mortality were recorded between groups exposed to bacteria alone or bacteria in combination with the higher dose of Clophen A50 (21.6 and 20.4%, respectively). Decreased disease resistance was recorded in groups exposed to F. psychrophilum and the lower dose of Clophen A50, with a mean cumulative mortality of 56.0%. These results could be due to non dose-dependent effects on the immune system, or toxic effects of PCB or their metabolites on the bacteria in groups exposed to the higher dose of Clophen A50. The present study indicates that maternal transfer of PCB might affect disease resistance to vertically transmitted F. psychrophilum.     

A study of dose response and organ susceptibility of copper toxicity in a rat model

Copper (Cu) in higher concentration is toxic and results in various organ dysfunction. We report Cu concentration in liver, brain and kidney in the rat model following chronic exposure of oral copper sulphate at different subtoxic doses and correlate the tissue Cu concentrations with respective organ dysfunction. Fifty-four male wistar rats divided in 3 groups, the control group received saline water and the experimental group (Group-IIA and IIB) received oral copper sulphate in dose of 100 and 200 mg/kg Body Weight. At the end of 30 days, 60 days and 90 days of exposure, six rats were sacrificed from each group. The maximum peak force in grip strength, latency to fall in rotarod and percentage attention score in Y-maze were significantly reduced in the copper sulphate exposed rats compared to the controls at all time points and these were more marked in Group-IIB compared to Group-IIA. Cu concentration was significantly higher in liver, kidney and brain in the Group-II compared to the Group-I. The Cu concentration was highest in the liver (29 folds) followed by kidney (3 folds) and brain (1.5 folds). Serum ALT, AST and bilirubin correlated with liver Cu, BUN with kidney Cu, and grip strength, rotarod and Y-maze findings correlated with brain Cu level. In rats, chronic oral copper sulphate exposure at subtoxic level results in neurobehavioral abnormality and liver and kidney dysfunctions due to increased Cu concentration in the respective organs. Liver is the most vulnerable organ and copper toxicity increases with increasing dose and duration of exposure.     

Nanoinjection as a tool to mimic vertical transmission of Flavobacterium psychrophilum in rainbow trout Oncorhynchus mykiss

Newly fertilised eggs of rainbow trout Oncorhynchus mykiss were nanoinjected with Flavobacterium psychrophilum in order to mimic vertical transmission. Two bacterial isolates with different elastin-degrading capacity were used. All infected groups (10, 100 and 1000 colony forming units egg(-1)) showed significantly higher cumulative mortalities than the control groups at the end of the experiment, 70 d post-hatching. The total mortalities in the control groups were below 2.5%. In the high-dose groups, 95 to 100% of the eggs died during the eyed stage. In the intermediate group infected with the elastin-negative isolate, the major mortality occurred during the eyed stage of the egg, with a total cumulative mortality of 83% at the end of the experiment. In the intermediate group infected with the elastin-positive isolate, a total mortality of 63% was recorded. In this group, diseased fry showed clinical signs of disease and morphological changes similar to those described in connection with rainbow trout fry syndrome (RTFS) shortly after the beginning of feeding. In the low dose groups, the mortality in the elastin-negative group was 14% and in the elastin-positive group 11%. The bacterium was isolated from dead eggs and fry in infected groups and demonstrated in internal organs of dead and moribund fry by immunohistochemistry. The nanoinjection method used in this study may be a useful method to study pathogens, like F. psychrophilum, that can be vertically transmitted.     

Modelling time‐varying low‐temperature‐induced mortality rates for pupae of Tuta absoluta (Gelechiidae,Lepidoptera)

In a series of laboratory experiments, acclimated pupae of Tuta absoluta were exposed to various constant low temperatures in order to estimate their maximum survival times (Kaplan–Meier, Lt_99.99). A Weibull function was fitted to the data points, describing maximum survival time as a function of temperature. In another experiment at ?6°C, the progress of mortality increasing with exposure time was identified. These values were fitted by a sigmoidal function converging asymptotically to 100% mortality for very long exposure times. Analysing mortality data from the maximum survival experiment by a generalized linear model showed a significant common slope parameter (p < .001) that reveals parallelism of the survival curves at each temperature if a log time axis is used. These curves appear stretched (time scaled) if plotted with a nonlogarithmic time axis. By combining these mathematical relations, it was possible to calculate a species‐specific ‘mortality surface’ which exhibits mortalities, depending on temperature and duration of exposure. In order to accumulate hourly mortalities for courses of varying temperatures, an algorithm was developed which yields mortality values from that surface taking into account the attained mortality level. In validation experiments, recorded mortalities were compared against modelled mortalities. Prediction of mortality was partially supported by the model, but pupae experiencing intensely fluctuating temperatures showed decreased mortality, probably caused by rapid cold hardening during exposure. Despite this observation, mortality data converged to distinct levels very close to 100% depending on the intensity of temperature fluctuations that were characteristic for different types of experiments. The highest mortality limit occurred at intensely fluctuating temperatures in laboratory experiments. This constituted a benchmark that was not reached under various field conditions. Thus, it was possible to identify temperature limits for the extinction of field populations of Tuta absoluta pupae.     

Intrastadial developmental resistance of third instar gypsy moths (Lymantria dispar L.) to L. dispar nucleopolyhedrovirus

Gypsy moth larvae become increasingly resistant to lethal infection by the Lymantria dispar M nucleopolyhedrovirus (LdMNPV) as they age within the fourth instar. Newly molted larvae are most sensitive to infection, mid-instars are least sensitive, and late-instars display intermediate sensitivity. This resistance occurs whether the virus is delivered orally or intrahemocoelically. The present study reveals a nearly identical pattern of resistance in third instar larvae. An LD₄₈ dose of polyhedra for newly molted third instars produced 18%, 10%, 8%, 25%, and 24% mortalities in larvae to which virus was orally administered at 12, 24, 48, 72, and 96 hours post-molt (hpm), respectively, which is a 6-fold reduction in mortality between newly molted larvae and mid-instars. An LD₄₄ dose of budded virus for newly molted third instars produced 33%, 23%, 17%, 31%, and 31% mortalities when injected into larvae that were 12, 24, 48, 72, and 96 hpm, respectively, which is a 2.6-fold reduction in mortality between newly molted larvae and mid-instars, indicating that approximately half of this resistance is midgut-based and half is systemically based. Doubling the viral dose did not overcome developmental resistance whether the virus was delivered orally or intrahemocoelically. In addition, time to death was significantly affected by the time post-molt at which the insect was inoculated with the virus. We suggest that intrastadial developmental resistance may affect both the ecology and management of the gypsy moth.     

Effect of water temperature on the immune response and infectivity pattern of white spot syndrome virus (WSSV) in freshwater crayfish

The susceptibility of two species of freshwater crayfish, Pacifastacus leniusculus and Astacus astacus, to white spot syndrome virus (WSSV) by intramuscular injection was compared and the results show that both species are susceptible to WSSV. The effect of water temperature on the development of white spot disease in crayfish was also studied. Crayfish were exposed to different temperatures after WSSV injection or oral exposure and the mortalities were recorded over a period of 45 days. No mortality was observed when crayfish were held at 4+/-2 degrees C or 12+/-2 degrees C and reached 100% when these crayfish transferred to 22+/-2 degrees C. The mortalities of nearly moribund crayfish at 22+/-2 degrees C with WSSV could be delayed after transfer to temperature below 16 degrees C. These results clearly show that low temperature affects the WSSV pathogenicity in crayfish. Moreover, haemocyte counts, phenoloxidase activity, mRNA levels of prophenoloxidase (proPO) and the lipopolysaccharide and beta-1,3-glucan binding protein (LGBP) in crayfish exposed to various water temperatures were studied. Total haemocyte and granular cell counts of crayfish held at different temperatures were not significantly (P>0.05) different, except for the total haemocyte number at 18 degrees C was significantly (P<0.05) higher than in crayfish at 4 degrees C. The percentage of granular cells in crayfish held at 4 degrees C was the highest compared to crayfish maintained at other temperatures. The phenoloxidase activities in haemocyte lysate supernatant (HLS) of crayfish at all temperature groups remained similar. The amount of proPO-mRNAs in haemocytes was much higher than the amount of LGBP-m RNAs in all the experimental groups. However, there was no change in the level of pro PO-mRNA at the tested temperatures. Interestingly, the level of LGBP-mRNA of crayfish kept at 22 degrees C was much lower than in those held at lower temperatures. Proliferation of the haematopoietic tissues was higher at high temperatures which may support replication of WSSV, and explain the high mortality of crayfish with WSSV infection at high temperature. Based on these studies it is concluded that crayfish might act as a carrier of WSSV at low water temperature and could develop white spot disease if the water temperature is increased.     

Viral load of various tissues of rainbow trout challenged with viral haemorrhagic septicaemia virus at various stages of disease

Market-sized rainbow trout Oncorhynchus mykiss were challenged by waterborne exposure to viral haemorrhagic septicaemia virus (VHSV isolate of genogroup Ia). Fish were sampled at 4 stages of infection (before onset of clinical signs, clinically affected fish, mortalities and survivors) and the viral load determined in (1) internal organs, (2) muscle tissue and (3) brain and gill tissue. Virus levels were determined by virus titration and real-time RT-PCR. VHSV was detected by either method in the majority of fish before onset of clinical signs and in the survivor group as well as in all fish in the clinically affected fish and mortality groups. Mean virus amounts per mg of tissue determined by virus titration (TCID50) or real-time RT-PCR (copy number) were > 10(4) in preclinical fish, > 10(3.8) in clinically affected fish, > 10(3.9) in mortalities and > 10(1.2) in survivors. Virus levels tended to be highest in the internal organs of subclinical and clinically affected fish and in brain and gill tissue of survivors. The results demonstrate that significant levels of VHSV can be found in tissues of rainbow trout that may be marketed for human consumption, which may have relevance for the biosecurity of VHS-free areas.     

Susceptibility of European sheatfish Silurus glanis to a panel of ranaviruses

The current study was undertaken in order to assess the risk that different ranaviruses might impose on European sheatfish aquaculture. As the European sheatfish virus (ESV) is a known pathogen causing losses in European sheatfish aquaculture, it was assumed that closely related exotic ranaviruses might also be able to infect European sheatfish and probably cause disease and mortality in this species. The differential susceptibility of European sheatfish (Silurus glanis) to various ranavirus isolates was assessed at two different temperatures (15°C and 25°C) in a recirculation system. Fish were infected experimentally with a panel of ranavirus isolates including ESV, European catfish virus (ECV), European catfish virus isolate 24 (ECV‐24), Epizootic haematopoietic necrosis virus (EHNV), Rana esculenta virus isolate Italy 282/ I02 (REV), short‐finned eel virus (SERV), Bohle iridovirus (BIV), guppy virus 6 (GV6), doctor fish virus (DFV) and Frog virus 3 (FV3). Significant mortalities were observed, as expected, in fish infected with ESV at 15°C (100%) as well as at 25°C (86/83%). Fish infected with ECV at 15°C showed no clinical signs of disease (8% mortality), whereas those fish infected at 25°C exhibited a cumulative mortality of 54%. Fatal disease was also induced by Italian isolate ECV‐24 at 25°C (81%). Virus isolates ESV, ECV and ECV‐24, generally the most genetically closely related viruses, were successfully isolated from dead fish by cell culture with subsequent identification by polymerase chain reaction (PCR) and sequence analysis. However, no mortality or clinical signs of disease were observed in the groups of sheatfish infected with the other ranaviruses investigated in the study, and none of those viruses were re‐isolated in cell culture or identified by PCR. It was concluded that European sheatfish are susceptible to infection with ESV, ECV and ECV‐24 under laboratory conditions, but not to infection with EHNV, REV, SERV, BIV, GV6, DFV or FV3. For ESV, the incubation period was shorter at 25°C compared to 15°C water temperature, but whereas all fish died after ESV infection at 15°C, some fish survived the infection at 25°C. Futhermore, the very young sheatfish were susceptible to ECV and ECV‐24 at 25°C, whereas there was no significant mortality in the group of older sheatfish challenged with ECV at 15°C. Therefore, the clinical characteristics of the disease seem to depend on the age of the fish as well as on the water temperature.     

Susceptibility of juvenile Atlantic cod Gadus morhua to viral haemorrhagic septicaemia virus isolated from wild-caught Atlantic cod

A European strain of viral haemorrhagic septicaemia virus (VHSV) isolated from wild-caught cod Gadus morhua (H16/7/95) was shown to cause clinical disease and mortality in excess of 80% in juvenile Atlantic cod when administered by the intra-peritoneal (i.p.) route. No virus was recovered from cod cohabiting with experimentally infected fish at a ratio of 1:1, and no VHSV-associated mortality was demonstrated following immersion infection. External signs of disease in cod were the presence of exophthalmia and ascites. Virus was identified as VHSV by enzyme-linked immunosorbent assay (ELISA) and was recovered from both brain and organ pools (kidney, liver and spleen) of 100% of i.p. infected cod mortalities. Virus was also detected using an indirect immunofluorescence test on tissue imprints of kidney, liver, spleen and brain taken from moribund fish. The fact that cod were not susceptible to VHSV following waterborne exposure raises important questions surrounding the propagation, maintenance and impact of a naturally occurring reservoir of virus in the marine environment.     

Mortality among Canadian military personnel exposed to low-dose radiation.

We carried out a cohort study of mortality among 954 Canadian military personnel exposed to low-dose ionizing radiation during nuclear reactor clean-up operations at Chalk River Nuclear Laboratories, Chalk River, Ont., and during observation of atomic test blasts in the United States and Australia in the 1950s. Two controls matched for age, service, rank and trade were selected for each exposed subject. Mortality among the exposed and control groups was ascertained by means of record linkage with the Canadian Mortality Data Base. Survival analysis with life-table techniques did not reveal any difference in overall mortality between the exposed and control groups. Analysis of cause-specific mortality showed similar mortality patterns in the two groups; there was no elevation in the exposed group in the frequency of death from leukemia or thyroid cancer, the causes of death most often associated with radiation exposure. Analysis of survival by recorded gamma radiation dose also did not show any effect of radiation dose on mortality. The findings are in agreement with the current scientific literature on the risk of death from exposure to low-dose radiation.     

Antioxidant defenses and biochemical changes in the neotropical fish pacu, Piaractus mesopotamicus: Responses to single and combined copper and hypercarbia exposure

This study investigated the potentially detrimental effects of copper and elevated aquatic CO(2) (hypercarbia), alone or in combination, on pacu, Piaractus mesopotamicus. Fish were exposed for 48h to control (no copper addition in normocarbia), to 400μg Cu(2+)L(-1), to hypercarbic (1% CO(2); PCO(2)=6.9mm Hg) water and to 400μg Cu(2+)L(-1)+hypercarbia. In liver the single factors caused an increase in lipid hydroperoxide concentration that was not observed when the factors were combined. Copper exposure elicited increased hepatic superoxide dismutase activity, irrespective of aquatic CO(2) level. On the other hand, the effects of copper on hepatic glutathione peroxidase activity were dependent on water CO(2) levels. The two stressors combined did not affect hepatic catalase activity. Hypercarbic water caused a decline in plasma glucose concentration, but this was not observed when hypercarbia was combined with copper exposure. Copper caused a decrease in branchial Na(+)/K(+)-ATPase activity that was independent of water CO(2) level. Copper caused an increase in branchial metallothionein concentration that was independent of water CO(2) level. Thus, branchial metallothionein and Na(+)/K(+)-ATPase were effective biomarkers of copper exposure that were not affected by water CO(2) level.     

The effect of high fluoride intake on tissue trace elements and histology of testicular tubules in the rat

1. Male Wistar rats were exposed to fluoride (F) at concentrations of 100- and 200 ppm in their drinking water for 6- and 16 weeks.2. The high F intake caused several-fold increase in the F concentrations in the testes and bone as compared with control rats, both after the 6- and 16wk exposure; the bone F, but not testicular F, appeared to increase with dose and time.3. F exposure (100- and 200 ppm) decreased significantly the concentrations of zinc (Zn) in the testes, plasma, liver and kidneys particularly in the 16 wk groups; in the bone Zn tended to increase, however.4. The iron concentrations of the testes and plasma were not affected by F, whereas those of the liver, kidneys and bone appeared to increase under the influence of F.5. The concentrations of copper and manganese in the testes, liver and kidneys were not changed by F exposure.6. Fifty percent of the 100- and 200 ppm F rats after 16 weeks exhibited histopathologic changes in the germinal epithelium of the testes, which resembled those in Zn-deficient rats.7. The data suggest that a deprivation of testicular Zn due to a high F intake may be directly responsible for the injury of testicular tubules.     

Epizootiology and pathology of juvenile oyster disease in the Eastern oyster, Crassostrea virginica.

Juvenile Oyster Disease (JOD) causes mortalities of small cultured oysters, Crassostrea virginica. The present study was an intensive epizootiological and pathological investigation of JOD in eight sequentially deployed cohorts at sites on Long Island, New York. JOD symptoms and mortalities began in all groups at about the same time. Lesions on the mantle were detected histologically about 1 week before the principal symptom, a conchiolin deposit on the inner shell, appeared. Mortality began about 1 week later and reached 60-90% in oysters <25 mm. Mantle lesions were highly correlated with subsequent conchiolin-deposit prevalence and with total mortality. Larger juveniles (25-40 mm) were affected by the disease and produced conchiolin deposits, but mortalities did not exceed 30%. Mortalities were consistently related to size, but not necessarily to age or length of "exposure" in the field. There was no indication that JOD was linked to a particular broodstock or hatchery. Wild spat deployed at experimental sites showed JOD symptoms before the hatchery-produced groups did and cohorts maintained inside a hatchery experienced essentially no JOD. Histological examination of cohorts experiencing high mortalities failed to reveal an obvious etiological agent, but showed a disease pattern similar to that described for other bivalve diseases with a bacterial etiology. Similarities and differences between this and other studies of JOD suggest that one or more bacterial species is responsible for JOD, but that a trigger, probably temperature, is also involved and may vary from site to site.     

Assessment of the effect of alpha-galactosides injected during embryogenesis on selected chicken traits

The effect of different doses of alpha-galactoside (RFOs) preparations from Pisum sativum L. cv. Opal, injected into eggs during embryogenesis, on maintaining a high number of bifidobacteria, selected chicken broiler traits and the lipoprotein level of blood were studied. Two independent experiments were conducted. In the first, Ringer water solution containing 1.763 mg/egg of fructooligosaccharides (FOS) (I group), 2.1158 mg of pea RFO preparation containing 20% sucrose (II group) and 0.4232 mg of sucrose (III group) were injected into Hubbard broiler breeder eggs containing 12-day old embryos. Only Ringer water solution was applied to the eggs of the control group (IV group). The number of bifidobacteria determined in faeces of two-day old chicken of groups I and II was significantly higher in comparison with the sucrose and control groups. The high level ofbifidobacteria of groups I and II was maintained during 6 weeks. The dose of both preparations had no influence on the body weight, carcass, breast muscle, leg and abdominal fat ratio, total cholesterol, HDL and LDL serum concentrations. Broiler mortality and breast muscle cholesterol concentration was highest (P < 0.05) for the control group. On the other hand, the European Production Index, as well as serum triglycerides, were the lowest for this group. The second experiment was performed on Hybro G chicken breeder eggs. 0.69, 3.43 and 6.87 mg/egg of pea RFO preparation doses containing 20% sucrose were injected into the experimental groups. The number of bifidobacteria in the caecum and selected meat traits of broilers were determined. The results of this experiment confirmed that RFO injection in ovo causes the long-time maintenance of a high level ofbifidobacteria. The dose of the preparations does not have any effect on the selected broiler meat traits, except that the highest dose increases the percent of carcase in body weight. However, this dose reduced the hatchability of the treated embryos.     

Radiation-induced bystander effects in the Atlantic salmon (salmo salar L.) following mixed exposure to copper and aluminum combined with low-dose gamma radiation

Very little is known about the combined effects of low doses of heavy metals and radiation. However, such “multiple stressor” exposure is the reality in the environment. In the work reported in this paper, fish were exposed to cobalt 60 gamma irradiation with or without copper or aluminum in the water. Doses of radiation ranged from 4 to 75 mGy delivered over 48 or 6 h. Copper doses ranged from 10 to 80 μg/L for the same time period. The aluminum dose was 250 μg/L. Gills and skin were removed from the fish after exposure and explanted in tissue culture flasks for investigation of bystander effects of the exposures using a stress signal reporter assay, which has been demonstrated to be a sensitive indicator of homeostatic perturbations in cells. The results show complex synergistic interactions of radiation and copper. Gills on the whole produce more toxic bystander signals than skin, but the additivity scores show highly variable results which depend on dose and time of exposure. The impacts of low doses of copper and low doses of radiation are greater than additive, medium levels of copper alone have a similar level of effect of bystander signal toxicity to the low dose. The addition of radiation stress, however, produces clear protective effects in the reporters treated with skin-derived medium. Gill-derived medium from the same fish did not show protective effects. Radiation exposure in the presence of 80 μg/L led to highly variable results, which due to animal variation were not significantly different from the effect of copper alone. The results are stressor type, stressor concentration and time dependent. Clearly co-exposure to radiation and heavy metals does not always lead to simple additive effects.     

Copper and the herbicide atrazine impair the stress response of the freshwater fish Prochilodus lineatus

In order to evaluate the effects of copper and atrazine on the stress response of the freshwater fish Prochilodus lineatus, juvenile fish were pre-exposed to copper (20 μg L(-1)) or atrazine (10 μg L(-1)) for 24 h and then submitted to air exposure for 3 min. Simultaneously fish kept in dechlorinated water for 24 h were subjected to air exposure and a non-stress group was not subjected to air stress or any contaminants. Animals were sampled immediately (t0) and after 1, 3 and 6 h of air exposure (t1, t3 and t6 respectively) for the analysis of plasma cortisol, glucose and Na(+), hepatic glycogen, branchial Na(+)/K(+)-ATPase (NKA), number of red blood cells per cubic millimeter of blood (RBC), hematocrit (Hct) and hemoglobin content (Hb). In fish pre-exposed to copper the stress response was inhibited, and at t1 and t3 both cortisol and glucose remained significantly lower compared to fish subjected to air stress only. In fish pre-exposed to atrazine there was no rise in cortisol, but there was an increase in plasma glucose, RBC, Hct and Hb at t0 and a return of these parameters to basal levels at t1, as they did not differ significantly in relation to non-stressed fish. Animals pre-exposed to either Cu or atrazine showed a significant reduction in NKA activity at t1 and t3, in relation to air stressed fish. These results clearly indicate that copper and atrazine impair cortisol stress response of P. lineatus and that fish subjected to a contaminant-induced stress, either by copper or atrazine, may not be able to respond to any additional stressors.     

Killer Whale (Orcinus orca) Deaths in Prince William Sound,Alaska, 1985–1990

During 1985–1990, two groups of killer whales in Prince William Sound, Alaska, experienced unusually high rates of mortality, while seven others did not. Those affected were AB pod, part of the southern Alaska population of resident (fish-eating) killer whales, and the AT1 transient (marine mammal–eating) group, a very small, reproductively isolated population that last reproduced in 1984. In 1985–1986, several AB pod members were shot by fishermen defending their catch from depredation, which explains some of the deaths. Understanding the other deaths is complicated by the Exxon Valdez oil spill (March 1989) and uncertainties about the causes and times of the deaths. For AB pod, possible factors involved in the post-spill mortalities are delayed effects of bullet wounds, continued shooting, oil exposure, and consequences of being orphaned. For the AT1 group, possible factors are oil exposure, small population size, old age, and high-contaminant burdens. An analysis of possible effects of inhalation of volatile organic compounds, contact with the oil slick, and ingestion of oil with water or prey did not reveal route(s) of exposure that could explain the mortalities. The cause(s) of the killer whale deaths recorded following the oil spill remain uncertain.