Seasonal simulated photoperiods influence melatonin release and immune markers of pike perch Sander lucioperca.

Melatonin is considered as the time-keeping hormone acting on important physiological functions of teleosts. While the influence of melatonin on reproduction and development is well described, its potential role on immune functions has little been considered. In order to better define an immune modulation by the melatonin hormone, we hypothesized that natural variations of photoperiod and subsequent changes in melatonin release profile may act on immune status of pikeperch. Therefore, we investigated during 70 days the effects of two photoperiod regimes simulating the fall and spring in western Europe, on pikeperch physiological and immune responses. Samples were collected at 04:00 and 15:00 at days 1, 37 and 70. Growth, plasma melatonin levels, innate immune markers and expression of immune-relevant genes in head kidney tissue were assessed. While growth and stress level were not affected by the seasonal simulated photoperiods, nocturnal levels of plasma melatonin were photoperiod-dependent. Innate immune markers, including lysozyme, complement, peroxidase and phagocytic activities, were stimulated by the fall-simulated photoperiod and a significant correlation was made with plasma melatonin. In addition to bring the first evidence of changes in fish immunocompetence related to photoperiod, our results provide an additional indication supporting the immunomodulatory action of melatonin in teleosts.

Patterns of mercury and selenium exposure in minnesota common loons.

Common loons (Gavia immer) are at risk of elevated dietary mercury (Hg) exposure in portions of their breeding range. To assess the level of risk among loons in Minnesota (USA), we investigated loon blood Hg concentrations in breeding lakes across Minnesota. Loon blood Hg concentrations were regressed on predicted Hg concentrations in standardized 12-cm whole-organism yellow perch (Perca flavescens), based on fish Hg records from Minnesota lakes, using the US Geological Survey National Descriptive Model for Mercury in Fish. A linear model, incorporating common loon sex, age, body mass, and log-transformed standardized perch Hg concentration representative of each study lake, was associated with 83% of the variability in observed common loon blood Hg concentrations. Loon blood Hg concentration was positively related to standardized perch Hg concentrations; juvenile loons had lower blood Hg concentrations than adult females, and blood Hg concentrations of juveniles increased with body mass. Blood Hg concentrations of all adult common loons and associated standardized prey Hg for all loon capture lakes included in the study were well below proposed thresholds for adverse effects on loon behavior, physiology, survival, and reproductive success. The fish Hg modeling approach provided insights into spatial patterns of dietary Hg exposure risk to common loons across Minnesota. We also determined that loon blood selenium (Se) concentrations were positively correlated with Hg concentration. Average common loon blood Se concentrations exceeded the published provisional threshold. Environ Toxicol Chem 2019;38:524-532. Published 2018 Wiley Periodicals Inc. on behalf of SETAC. This article is a US government work and, as such, is in the public domain in the United States of America.

Plasma biomarkers in juvenile marine fish provide evidence for endocrine modulation potential of organotin compounds.

Organotin compounds, such as tributyltin (TBT) and triphenyltin (TPT), have been widely used to control marine fouling. Here, we show that organotin stimulation reduces the hormone levels in the plasma of two economically important aquaculture fish. Blood plasma samples were collected from juvenile red seabream and black rockfish exposed to environmentally realistic concentrations of TBT and TPT for 14 days. The levels of two plasma biomarkers, namely the yolk protein precursor vitellogenin (VTG) and the sex steroid 17ß-estradiol (E2), were measured to determine the endocrine disrupting potential of the organotin compounds. Both organotin compounds were dose-dependently accumulated in the blood of two fish. Exposure to waterborne TBT and TBT significantly decreased the plasma VTG levels in both the juvenile fish in a dose-dependent manner. In contrast, the treatment with E2, a well-known VTG inducer, significantly increased the plasma VTG levels in both the fish. In addition, the mRNA levels of vtg were also downregulated in the liver tissues of both the fish at 100 and/or 1000 ng L-1 of TBT or TPT exposure. The plasma E2 titers were significantly suppressed at 100 and/or 1000 ng L-1 of TBT or TPT exposure for 14 days compared to their titer in the control. Since estrogen directly regulates vtg gene expression and VTG synthesis, our results reveal the endocrine disrupting potential of organotin compounds, and subsequently the endocrine modulation at early stage of fish can trigger further fluctuations in sexual differentiation, maturation, sex ration or egg production. In addition, the results demonstrate their effects on non-target organisms, particularly on animals reared in aquaculture and fisheries.

Impact of inducing general anesthesia with Propiscin (etomidate) on the physiology and health of European perch (Perca fluviatilis L.).

The aim of the study was to describe the course and timing of the different stages of anesthesia induced with Propiscin (etomidate) on juvenile European perch (experiment I) and to describe the effect of immersing specimens of this species had on selected hematological and biochemical parameters (experiment II). The study was conducted on material with body weights (BW) of 162.98 (experiment I) and 171.60 g (experiment II). In experiment I, general anesthesia was induced with two different anesthetic concentrations (1 or 2 ml l-1; anesthesia time 10 min). In experiment II, blood was drawn for hematological and biochemical analyses from the fish that had been exposed to anesthetic immersion baths with two different concentrations of Propiscin (1 and 2 ml l-1) and for different exposure times (3 and 10 min). Blood samples were collected immediately following immersion (0 h) and 24 h later (24 h). Specimens that were immersed at the higher concentration of anesthetic achieved subsequent stages of general anesthesia two times faster (P ≤ 0.05). However, during recovery, some statistically significant differences were observed, but these lasted only until stage I was achieved. Among the hematological parameters (0 h), significant differences were observed in hematocrit (HCT) and mean corpuscular volume (MCV), while among the biochemical determinations (0 h), statistically significant differences were noted in the concentrations of glucose, calcium, lactate, and ammonia. After 24 h, the levels of these parameters in all fish groups returned to initial values. The hematological and biochemical tests conducted permit concluding that the anesthetic tested, at the concentrations (1 and 2 ml l-1) and the exposure times of up to 10 min at which it was tested, is safe and can be used successfully to induce general anesthesia in perch.

Plasma osmolality and oxygen consumption of perch Perca fluviatilis in response to different salinities and temperatures.

The present study determined the blood plasma osmolality and oxygen consumption of the perch Perca fluviatilis at different salinities (0, 10 and 15) and temperatures (5, 10 and 20° C). Blood plasma osmolality increased with salinity at all temperatures. Standard metabolic rate (SMR) increased with salinity at 10 and 20° C. Maximum metabolic rate (MMR) and aerobic scope was lowest at salinity of 15 at 5° C, yet at 20° C, they were lowest at a salinity of 0. A cost of osmoregulation (SMR at a salinity of 0 and 15 compared with SMR at a salinity of 10) could only be detected at a salinity of 15 at 20° C, where it was 28%. The results show that P. fluviatilis have capacity to osmoregulate in hyper-osmotic environments. This contradicts previous studies and indicates intraspecific variability in osmoregulatory capabilities among P. fluviatilis populations or habitat origins. An apparent cost of osmoregulation (28%) at a salinity of 15 at 20° C indicates that the cost of osmoregulation in P. fluviatilis increases with temperature under hyperosmotic conditions and a power analysis showed that the cost of osmoregulation could be lower than 12·5% under other environmental conditions. The effect of salinity on MMR is possibly due to a reduction in gill permeability, initiated to reduce osmotic stress. An interaction between salinity and temperature on aerobic scope shows that high salinity habitats are energetically beneficial during warm periods (summer), whereas low salinity habitats are energetically beneficial during cold periods (winter). It is suggested, therefore, that the seasonal migrations of P. fluviatilis between brackish and fresh water is to select an environment that is optimal for metabolism and aerobic scope.

Thermal acclimation in the perch (Perca fluviatilis L.) immunity.

Fish immune systems must be able to cope with pathogens over a wide temperature range. Earlier research suggest that fish are more dependent on innate immune responses based on pattern recognition than acquired functions with specific recognition. If this applies to phagocytes, then opsonins (serum factors that augment phagocytosis e.g. immunoglobulins and complement proteins) attached on zymosan (Z) particles should be recognized better at higher temperatures than Z only. Z is recognized by glucan receptor representing pattern recognition. In this study perch were acclimated to 5 °C or 16 °C for 3-5 weeks. The recognition and activation of respiratory burst reaction of peripheral blood phagocytes was examined at seven different measurement temperatures (5, 10, 16, 20, 24 27, and 30 °C) when the cells were stimulated with Z and serum opsonized zymosan (OZ). Respiratory burst was measured as luminol chemiluminescence (CL) from diluted whole blood. OZ-induced CL per volume of blood was on average approximately 4.6 times higher in 16 °C acclimated fish than 5 °C acclimated perch (P<0.0001). Z-induced CL was approximately 3 times higher at lower temperatures in 16 °C acclimated perch than 5 °C acclimated fish and 6-9 times higher at 27 °C and 30 °C (P<0.001), respectively. CL reaction kinetics were faster in perch acclimated to 5 °C than 16 °C -acclimated fish, especially at low temperatures (P<0.001). Thermal acclimation caused a 3-4 °C shift in temperature response curves of CL towards the acclimation temperature (P<0.0001 and P<0.053 in Z and OZ-induced CL, respectively). Serum opsonins activated perch phagocytes substantially better at higher temperatures in both acclimation groups, which is consistent with an earlier study in rainbow trout (O. mykiss). However, opsonin recognition was significantly better in 16 °C acclimated perch than 5 °C acclimated fish, which was seen as higher CLs for OZ compared to Z, especially at higher temperatures. This is opposite to previously reported results in rainbow trout. Differences between rainbow trout and perch in opsonin recognition by blood phagocytes suggest that the living habits of perch, which prefers approximately a 10 °C higher temperature than rainbow trout, may be reflected in immune cell functions. Results of the present examination suggest that also in fish phagocytes pattern recognition is the prevailing system at low temperatures, and specific recognition is more effective at high temperatures.

First evidence of the possible implication of the 11-deoxycorticosterone (DOC) in immune activity of Eurasian perch (Perca fluviatilis, L.): comparison with cortisol.

Cortisol, the main corticosteroid in fish, is frequently described as a modulator of fish immune system. Moreover, 11-deoxycorticosterone (DOC) was shown to bind and transcriptionally activate the mineralocorticoid receptor and may act as a mineralocorticoid in fish. Immune modulations induced by intraperitoneal injections of these two corticosteroids were assessed in Eurasian perch juveniles. Cortisol and DOC were injected at 0.8 mg kg(-1) and 0.08 mg kg(-1) body weight respectively. Cortisol increased plasma lysozyme activity 72 h post-injection, C-type lysozyme expression in spleen from 1 to 72 h post-injection, and favoured blood neutrophils at the expense of a mixture of lymphocytes and thrombocytes. Moreover, 6 h after injection, cortisol reduced expression levels of the pro-inflammatory cytokine TNF-α in spleen. DOC had no effects on the immune variables measured in plasma, but increased expression levels of C-type lysozyme and apolipoprotein A1 mRNA in both gills and spleen. Meanwhile, DOC stimulated its putative signalling pathway by increasing expression of mineralocorticoid receptor and 11ß-hydroxysteroid dehydrogenase-2 in spleen. These results confirmed the role of cortisol as an innate, short term immune stimulator. For the first time, DOC is described as a possible immune stimulator in fish.

Comparison of the effects of four anaesthetics on haematological and blood biochemical profiles in pikeperch (Sander lucioperca L.).

OBJECTIVES: The objectives of the study were to compare the effects of Propiscin, 2-phenoxyethanol, clove oil and tricaine methane sulphonate (MS 222), anaesthetics frequently used in aquaculture. DESIGN: The haematological and biochemical blood profiles of pikeperch (Sander lucioperca L.) anesthetized with Propiscin (1.5 ml L-1), 2-phenoxyethanol (0.3 ml L-1), clove oil (33 mg L-1), MS 222 (150 mg L-1) and non-anesthetized control group were tested. Each tested group was divided into two subgroups, the first subgroup was sampled in anaesthesia 10 min after application of the anaesthetic and the second one live on 24h. RESULTS: The erythrocyte count and haematocrit was significantly decreased in 2-phenoxyethanol (24 h) compared with control group (CG). The mean corpuscular haemoglobin concentration was significantly increased in 2-phenoxyethanol (10 min), Propiscin (10 min and 24 h) compared to CG. The 2-phenoxyethanol (10 min and 24 h), MS 222 (24 h), clove oil (24 h), and Propiscin (10 min and 24 h) showed significantly lower leukocyte count compared with CG. The level of glucose was significantly (p<0.05) elevated with MS 222 (10 min) and clove oil (10 min) compared with CG. The 2-phenoxyethanol (10 min and 24 h), MS 222 (24 h), clove oil (24 h), and Propiscin (24 h) showed significantly lower (p<0.01) ammonia levels compared with CG. The triacylglycerols was significantly decreased (p<0.01) with Propiscin (10 min and 24 h), MS 222 (24 h), clove oil (24 h) and with 2-phenoxyethanol (24 h) compared with CG. After 24 hours MS 222 (24 h) and Propiscin (24 h) anaesthesia, fish showed significantly lower (p<0.01) concentration of inorganic phosphate compared with CG. CONCLUSIONS: On the basis of this experiment, it appears that clove oil was associated with the lowest effects in pikeperch and therefore would be recommended as an alternative to MS 222, while Propiscin and 2-phenoxyethanol are not suitable for manipulation with pikeperch in aquaculture.

Residue depletion of albendazole and its metabolites in aquacultured yellow perch (Perca flavescens).

Metabolism and residue depletion studies are conducted to determine the marker residue (MR) of a drug in a target tissue of food animals. The MR is used to monitor potential unauthorized use of drugs. The current work is a continuation of our efforts to study metabolism and depletion profiles of albendazole in multiple finfish species to determine a common MR. The results of this study suggest that albendazole sulfone metabolite could potentially serve as MR for albendazole in yellow perch muscle, similar to channel catfish and hybrid striped bass as reported previously by us.

Physiological and proteomic evidences that domestication process differentially modulates the immune status of juvenile Eurasian perch (Perca fluviatilis) under chronic confinement stress.

The current study aimed to evaluate the influence of domestication process on the stress response and subsequent immune modulation in Eurasian perch juveniles (Perca fluviatilis) submitted to chronic confinement. Briefly, F1 and F4 generations were confined into small-size tanks and sampled 7 and 55 days after stocking. Cortisol and glucose levels as well as lysozyme activity and immunoglobulin level were evaluated in the serum. Spleen Somatic Index and spleen ROS production were also measured. A proteomic analysis was performed on serum sampled on day 7. Finally, both generations were genetically characterized using a microsatellite approach. Globally, results revealed that chronic confinement did not elicit a typical stress response but resulted in a prolonged immune stimulation. Proteomic results suggested that domestication process influenced the immune status of perch submitted to chronic confinement as the F1 confined fish displayed lower abundance of C3 complement component, transferrin and Apolipoprotein E. Microsatellite data showed a strong genetic drift as well as reduced genetic diversity, allelic number and heterozygosity along with domestication process. The present work is the first to report that fish under domestication can develop an immune response, assessed by a combined approach, following recurrent challenges imposed by captive environment despite a reduced genetic variation.

Plasma cortisol and hypothalamic monoamine responses in yellow perch Perca flavescens after intraperitoneal injection of lipopolysaccharide.

The concentrations of monoamines in the hypothalamus were determined in yellow perch Perca flavescens before and after injection with lipopolysaccharide (LPS; 3 mg kg⁻¹ fish weight) or saline to test for the presence of neurochemical changes potentially associated with changes in plasma cortisol characteristic of intraperitoneal (ip) challenge with LPS. In the first experiment, yellow perch were injected with saline or LPS and the hypothalamus removed and plasma sampled before and at 0.5, 1.5, 3.0, and 6 h after injection. Plasma cortisol was elevated in both saline- and LPS-injected fish through 1.5 h after injection and returned to levels resembling pre-injection by 3 h after injection. Significantly higher amounts of cortisol in plasma from LPS-injected relative to saline-injected fish were observed 6 h following injection. A significant decrease relative to levels observed 0.5-3 h after handling was observed in serotonin concentrations at 6 h following LPS and saline injection with a concomitant increase in the ratio of 5-hydroxyindoleacetic acid:serotonin. In the second experiment, hypothalamic monoamines were sampled before and at 3, 6, 9, 12, and 24 h after injection with LPS or saline. Significant increases from pre-injection levels were observed in the ratio 5-hydroxyindoleacetic acid:serotonin at 9, 12, and 24 h after injection, but no differences were detected between LPS- and saline-injected fish. These results support a model linking serotonergic system activation following handling stress, but no correlations with the sustained elevations of plasma cortisol associated with inflammatory challenge were observed.

Steroid determination in fish plasma using capillary electrophoresis.

A capillary separation method that incorporates pH-mediated stacking is employed for the simultaneous determination of circulating steroid hormones in plasma from Perca flavescens (yellow perch) collected from natural aquatic environments. The method can be applied to separate eight steroid standards: progesterone, 17alpha,20beta-dihydroxypregn-4-en-3-one, 17alpha-hydroxyprogesterone, testosterone, estrone, 11-ketotestosterone, ethynyl estradiol, and 17beta-estradiol. Based on screening of plasma, the performance of the analytical method was determined for 17alpha,20beta-dihydroxypregn-4-en-3-one, testosterone, 11-ketotestosterone, and 17beta-estradiol. The within-day reproducibility in migration time for these four steroids in aqueous samples was < or =2%. Steroid quantification was accomplished using a calibration curve obtained with external standards. Plasma samples from fish collected from the Choptank and Severn Rivers, Maryland, USA, stored for up to one year were extracted with ethyl acetate and then further processed with anion exchange and hydrophobic solid phase extraction cartridges. The recovery of testosterone and 17beta-estradiol from yellow perch plasma was 84 and 85%, respectively. Endogenous levels of testosterone ranged from 0.9 to 44 ng/ml, and when detected 17alpha,20beta-dihydroxypregn-4-en-3-one ranged from 5 to 34 ng/ml. The reported values for testosterone correlated well with the immunoassay technique. Endogenous concentrations of 17beta-estradiol were < or =1.7 ng/ml. 11-Ketotestosterone was not quantified because of a suspected interferant. Higher levels of 17alpha,20beta-dihydroxypregn-4-en-3-one were found in male and female fish in which 17beta-estradiol was not detected. Monitoring multiple steroids can provide insight into hormonal fluctuations in fish.

Effects of anesthesia and surgery on serial blood gas values and lactate concentrations in yellow perch (Perca flavescens), walleye pike (Sander vitreus), and koi (Cyprinus carpio).

OBJECTIVE-To evaluate serial blood gas values and lactate concentrations in 3 fish species undergoing surgery and to compare blood lactate concentrations between fish that survived and those that died during the short-term postoperative period. DESIGN-Prospective cohort study. Animals-10 yellow perch, 5 walleye pike, and 8 koi. PROCEDURES-Blood samples were collected from each fish at 3 time points: before anesthesia, during anesthesia, and immediately after surgery. Blood gas values and blood lactate concentrations were measured. Fish were monitored for 2 weeks postoperatively. RESULTS-All walleye and koi survived, but 2 perch died. Blood pH significantly decreased in perch from before to during anesthesia, but increased back to preanesthesia baseline values after surgery. Blood Pco(2) decreased significantly in perch from before anesthesia to immediately after surgery, and also from during anesthesia to immediately after surgery, whereas blood Pco(2) decreased significantly in koi from before to during anesthesia. Blood Po(2) increased significantly in both perch and koi from before to during anesthesia, and also in koi from before anesthesia to immediately after surgery. For all 3 species, blood lactate concentrations increased significantly from before anesthesia to immediately after surgery. Blood lactate concentration (mean +/- SD) immediately after surgery for the 8 surviving perch was 6.06 +/- 1.47 mmol/L, which was significantly lower than blood lactate concentrations in the 2 nonsurviving perch (10.58 and 10.72 mmol/L). CONCLUSIONS AND CLINICAL RELEVANCE-High blood lactate concentrations following surgery in fish may be predictive of a poor short-term postoperative survival rate.

Ovarian steroidogenesis inhibition by constant photothermal conditions is caused by a lack of gonadotropin stimulation in Eurasian perch.

In fish, the reasons for the inhibition of reproduction by constant photothermal conditions of rearing are far from clear. In an in vivo experiment, two groups of females reared under natural (4-28 degrees C) or constant photothermal conditions (20-22 degrees C, photoperiod 12/12) were investigated for gonad development, sex-steroids (testosterone-T, 17-beta-estradiol-E2 and 11 Keto-Testosterone-11KT) dynamics and brain aromatase activity in January, February and March. Two days before each sampling date, a group of females reared under constant conditions was injected with HCG (Human Chorionic Gonadotropin: 100 UI/kg) and evaluated for the same parameters. In addition, in vitro ovarian steroidogenesis capacity for each female was determined with or without stimulation by HCG and/or IGF-1 (Insulin-like Growth Factor-1). The results indicate that vitellogenesis stage is the limit ovarian stage never reached in females submitted to constant photothermal conditions. This was associated with gonadogenesis delay and low levels of circulating sex-steroids (T, E2 and 11KT). Nevertheless, HCG injections partly counteracted the plasma steroid deprivation, indicating that ovaries from fish reared under constant photothermal conditions suffer from a lack of gonadotropin stimulation, maybe caused by plasma LH suppression. Such finding was confirmed by the in vitro ovary incubation test. HCG and IGF-1 treatments induced broad testosterone and 17-beta-estradiol elevations and the exposure to constant photothermal conditions, in some cases, decreased that response to HCG. In conclusion, we show that the inhibition of reproductive cycle in Eurasian perch females by constant photothermal conditions of rearing may be related to lower sex-steroid levels and to an inhibition of ovarian regulation by gonadotropins (at least LH), probably stopping gonadogenesis before vitellogenesis stage.

Exposure to low concentrations of dissolved ammonia promotes growth rate in walleye Sander vitreus.

The objective of the current study was to examine whether sublethal (moderate) levels of dissolved ammonia may be beneficial to growth in juvenile walleye Sander vitreus (recent evidence in juvenile rainbow trout Oncorhynchus mykiss has shown significant increases in protein synthesis in the presence of moderately elevated concentrations of dissolved ammonia). Moderately elevated dissolved ammonia concentrations between 100 and 300 micromol l(-1) suppressed routine aerobic metabolic activity by 20% during acute trials (2 h), while promoting specific growth rate (>50%) and elevating whole body soluble protein content by 20% in the early stages (14-42 days) in chronic ammonia exposure experiments. Juvenile S. vitreus held at ammonia concentrations between 107.6 +/- 5.5 and 225.5 +/- 4.7 micromol l(-1) (mean +/-s.e.) grew significantly faster than control fish and significantly reduced plasma cortisol levels (<3 microg dl(-1)). Results from this study suggest that chronic exposure to moderate amounts of dissolved ammonia significantly increase growth rates in juvenile S. vitreus by increasing nitrogen accessible for supplementary protein deposition leading to somatic development.

Plasma cortisol changes and body composition in Stizostedion lucioperca exposed to handling stress.

Stizostedion lucioperca aquaculture/stoking, remains a restrained industry due to several factors such as the paucity of freshwater resources and studies on the physiological responses of this species under environmental changes. The fish were subjected to handling stress by holding them out of the water in a hand-held dip net for 30 sec and netting the fish from the rearing tanks and transferring them to a small confinement tank. Sufficient aeration was supplied to the confinement tank to revert additional stress from oxygen depletion. Then measured changes in plasma cortisol levels and the growth ability (body composition) in Stizostedion lucioperca subjected to handling stress. Blood samples were collected from the fish after exposure to the handling stress. Crude protein (Nx6.25) was determined according to the Kjeldahl method, moisture content was determined by oven drying at 105+/-2 degrees C to constant weight and ash by heating in a muffle furnace at 550 degrees C to constant weight. Total lipids were extracted according to the Bligh and Dyer method. The results indicated that, handling stress significantly increased the plasma levels of cortisol 59.04 ng mL(-1) versus 40.83 ng mL(-1) in control group. Also the decrease of the level of protein and lipid concentrations show a significant difference between treatment and control (p<0.05). As protein and lipid decreased, moisture increased from 78.19% in control to 80.40% in treatment groups. According to the results, there was no significant change in ash content in control and treatment groups which was about 9%. In other words, it could be emphasized that nutrition-related behavior of Stizostedion lucioperca resulting from the activation of the hypothalamic/inter-renal axis in response to stress despite of different reactions bear resemblance to that of other fishes. Present data indicate that cortisol appears to be adequate to assess stress in Stizostedion lucioperca.

Thyroid disruption in walleye (Sander vitreus) exposed to environmental contaminants: cloning and use of iodothyronine deiodinases as molecular biomarkers.

Thyroid hormones play a role in the initiation of ovarian maturation in fish. Thus, reports of delayed sexual maturation in female walleye (Sander vitreus) exposed to contaminants in the Ottawa River suggest the presence of endocrine disrupting chemicals. The objectives of this study were to assess the effects of environmental contaminants in the Ottawa River on thyroid hormones of immature walleye and to develop a molecular biomarker of thyroid status. Walleye were sampled in the Ottawa River at Deep River (reference site), at Rivière Blanche (downstream from the Ottawa and Gatineau municipal wastewater treatment plants outflows), and at Plaisance (downstream from a pulp and paper mill). Plasma thyroid hormone levels were measured by radioimmunoassay. Walleye at Plaisance had two-fold elevated levels of thyroxine (T(4)) and 1.5-fold elevated levels triiodothyronine (T(3)), whereas the molar ratio of T(3):T(4) was reduced by over 50% compared to Deep River. Plasma T(3) levels were also elevated by approximately 1.5-fold at Rivière Blanche. Three iodothyronine deiodinases, a family of enzymes responsible for converting the prohormone T(4) to biologically active T(3), as well as for inactivating these two hormones, were partially cloned in walleye. A real-time PCR assay of deiodinase expression indicated that hepatic mRNA levels of type I and type III deiodinase were not modified between sites, whereas they were increased for type II deiodinase at Rivière Blanche as compared to the other sites. The response of this novel molecular transcript indicates a divergence with that expected based on the effects of experimentally induced hyperthyroidism on fish deiodinase expression; additional endpoints are therefore necessary to interpret changes in thyroid hormones levels in fish exposed to environmental contaminants.

Haematological responses of acute nitrite exposure in walleye (Sander vitreus).

Nitrite (NO2-) is a toxic intermediary of the bacterial oxidation of nitrogenous wastes (e.g. ammonia) in an aquatic environment. It becomes most lethal when oxygen becomes limited due to high fish densities or in the presence of high bacterial activity due to waste build-up-both situations commonly found in intensive aquaculture. To date however, little is known about how this toxin affects the physiology of walleye, an intended culture species, particularly in intensive re-circulating systems. This study aims to define threshold concentrations of nitrite that affect haemoglobin-oxygen affinity and carrying capacity in walleye. During in vivo tests, fish (N=20) were subjected to a medium effective concentration (EC50) of nitrite (0.9 mmol L(-1)) for 48 h while the effects of nitrite accumulation on blood properties were measured. The effects of oxygenation state on red blood cell (RBC) nitrite uptake and metHb formation was further investigated by in vitro tonometry. In vitro nitrite exposure to 3 mmol L(-1) resulted in a significantly higher methaemoglobin formation in 50% air saturated than 100% air saturated RBCs. Both cell water content and haematocrit decreased with time in 50% air saturated treatments, whereas total Hb remained constant, suggesting a reduction in RBC volume. Similar effects were observed during 48 h in vivo and in vitro nitrite exposure tests, indicating the reduction in RBC volume likely was not the result of a catecholamine response. Walleye were found to be tolerant to an accumulation of blood-NO2- levels similar to common carp, a highly Mean Cellular Volume (MCV) tolerant species, before succumbing to methaemoglobinemia. The elevated tolerance to nitrite of walleye is a beneficial characteristic for successful rearing in a culture setting, where reduced oxygen and elevated MCV levels are prevalent. The findings from this study may be used in developing guidelines for species-specific management of nitrogenous wastes in aquaculture.

Effects of stress on growth, cortisol and glucose levels in non-domesticated Eurasian perch (Perca fluviatilis) and domesticated rainbow trout (Oncorhynchus mykiss).

Eurasian perch (Perca fluviatilis) is a promising aquaculture candidate, but the growth performance of this non-domesticated species may be negatively affected by its stress responsiveness to intensive culture conditions. To evaluate this potential problem, juvenile Eurasian perch were exposed to a standardized handling stressor twice a week for an 8-week period. A similar study was conducted on domesticated rainbow trout (Oncorhynchus mykiss) for comparison of intra- and inter-specific differences. The stressed fish of both species showed lower body growth than the non-stressed control fish, however, the final mean body mass was 35.4% lower in the stressed Eurasian perch than in the non-stressed controls, compared to 22.8% difference between the two groups in rainbow trout. The stress responsiveness was examined by comparing the post-stress cortisol and glucose levels in repeatedly stressed fish and fish exposed to the stressor only once. The cortisol stress response in both species strongly indicated a habituation to the repeated stressor. Thus, repeatedly stressed Eurasian perch reached maximum cortisol levels of 130 ng/mL after 0.5 h compared to 200 ng/mL in the fish stressed once, while considerably smaller differences in cortisol levels were shown between the repeatedly and single stressed rainbow trout. Rainbow trout also showed lower post-stress glucose levels in the repeatedly stressed fish compared to the single stressed fish. In contrast, the glucose levels in both groups of Eurasian perch increased abruptly after stress treatment and remained elevated at approximately 19 mM for 6 h; levels were three times as high as the peak levels 3 h post-stress in rainbow trout. Together, the habituation of the stress response shown in both species did not eliminate the growth difference found in the repeatedly stressed fish versus the control fish. Further, the lower growth performance of Eurasian perch compared to rainbow trout could partly be due to the increased energy consumption in the more stress responsive Eurasian perch.

Are sex steroids involved in the sexual growth dimorphism in Eurasian perch juveniles?

Individual growth and food intake were monitored in Eurasian perch (Perca fluviatilis L.) juveniles (13.5+/-3.4 g initial body weight) to determine whether androgens and estrogens may mediate sex-related growth differences. Fish were individually tagged with chips and implanted with cocoa butter containing 20 microg of either 17alpha-methyltestosterone (MT) or 17beta-estradiol (E(2)) per gram of fish body; controls were implanted with cocoa butter without hormones. All fish were bled at the end of the experiment for measurement of E(2) in females and testosterone (T) in males (MT was not measured) and triiodothyronine (T3) in both genders. Survival, gonadosomatic index and hepatosomatic index were not affected by steroid treatments. Relative food intake (RFI), feed efficiency (FE) and specific growth rate (SGR) were higher in females than in males in all treatments. MT treatment significantly lowered RIF, FE and SGR in both sexes, while E(2) treatment showed no significant effect on growth and feeding parameters. In contrast to E(2) and T concentrations, T3 levels were significantly and positively correlated with SGR and RFI. The results provide evidence that MT may affect sexually related growth dimorphism by decreasing food intake and FE in Eurasian perch.