Chemotherapy of ectoparasite, Ergasilus ceylonensis of Asian cichlid, Etroplus suratensis

Therapeutic control of crustacean ectoparasite Ergasilus ceylonensis on gills of Asian cichlid Etroplus suratensis inhabiting Negombo estuary and its tributaries on the west coast of Sri Lanka was investigated using formalin, gammexane, potassium permanganate, 3,4 Dichloropropyoanilyde and fenitrothione. Potassium permanganate (3–5 ppm) and 3,4 Dichloropropyoanilyde (3–5 ppm) were observed to be successful as therapeutic chemicals. Infected fish were not able to tolerate low concentrations of formalin (50–500 ppm), gammexane (5 ppm) and fenitrothione (0.1–5.0 ppm).     

Variations in plasma melatonin levels of the rainbow trout (Oncorhynchus mykiss) under various light and temperature conditions

Daily variations in plasma melatonin levels in the rainbow trout Oncorhynchus mykiss were studied under various light and temperature conditions. Plasma melatonin levels were higher at mid-dark than those at mid-light under light-dark (LD) cycles. An acute exposure to darkness (2 hr) during the light phase significantly elevated the plasma melatonin to the level that is comparable with those at mid-dark, while an acute exposure to a light pulse (2 hr) during the dark phase significantly suppressed melatonin to the level that is comparable with those at mid-light. Plasma melatonin kept constantly high and low levels under constant darkness and constant light, respectively. No circadian rhythm was seen under both conditions. When the fish were subjected to simulative seasonal conditions (simulative (S)-spring: under LD 13.1:10.9 at 13 degrees C; S-summer: under LD 14.3:9.7 at 16.5 degrees C; S-autumn: under LD 11.3:12.7 at 13 degrees C; S-winter: under LD 10.1:13.9 at 9 degrees C), melatonin levels during the dark phase were significantly higher than those during the light phase irrespective of simulative seasons. The peak melatonin level in each simulative season significantly correlated with temperature but not with the length of the dark phase employed. In addition, the peak melatonin level in S-autumn was significantly higher than those in S-spring although water temperature was the same under these conditions. These results indicate that the melatonin rhythm in the trout plasma is not regulated by an endogenous circadian clock but by combination of photoperiod and water temperature.     

Impairment of the stress response in matrinxã juveniles (Brycon amazonicus) exposed to low concentrations of phenol

In this study we measured plasma cortisol, plasma glucose, plasma sodium and potassium, and liver and gill hsp70 levels in juvenile matrinxã (Brycon amazonicus) subjected to a 96 h exposure to phenol (0, 0.2, and 2.0 ppm), and the effect of this exposure on their ability to respond to a subsequent handling stress. Fish were sampled prior to initiation of exposure and 96 h, and at 1, 6, 12, and 24 h post-handling stress. During the 96 h exposure, plasma cortisol and glucose levels remained unchanged in all treatments. While plasma sodium levels were significantly reduced in all groups, plasma potassium levels only decreased in fish exposed to 0 and 0.2 ppm of phenol. Liver hsp70 levels decreased significantly at 96 h in fish exposed to 2.0 ppm of phenol. All groups, except fish exposed to 0.2 ppm of phenol, were able to increase plasma cortisol and glucose levels after handling stress. Fish exposed to 2.0 ppm of phenol showed decreased gill and liver hsp70 levels after the handling stress. Our data suggest that exposure to phenol may compromise the ability of matrinxã to elicit physiological responses to a subsequent stressor.     

Temperature dependent activation of leucocyte populations of rainbow trout, Oncorhynchus mykiss, after intraperitoneal immunisation with Aeromonas salmonicida

The temperature dependence of in vivo activation of rainbow trout Oncorhynchus mykiss, leucocyte populations after intraperitoneal injection (i.p.) of fish with a T-cell independent antigen Aeromonas salmonicida (strain MT423) was investigated using a proliferation assay and flow cytometric analysis with mab specific for trout leucocyte surface markers. In trout kept at 15-17 degrees C a prominent activation of blood and spleen leucocytes was found. Also, drastic changes of the percentage of the leucocyte populations in blood and spleen occurred: the amount of monocytes in the blood increased between day 2 and day 7 post injection (p.i.), whereas in spleen the amount of monocytes stayed at a high level (approximately 35%) after a depression between day 4 and day 7 p.i. The percentage of B-lymphocytes was increased first in spleen and then in blood. The percentage of granulocytes in blood was elevated during the whole experiment compared to control fish. In trout kept at 10-12 degrees C only blood leucocytes showed a weak activation after i.p. injection of A. salmonicida, whereas spleen leucocytes showed nearly no reaction. Only the percentage of granulocytes in the blood (day 2-14 p.i.) and of monocytes in the spleen (day 2 and day 8 p.i.) was changed compared to phosphate buffered saline (PBS)-injected fish. However, the development of A. salmonicida specific antibodies was contrary to the cellular reaction. Whereas antibodies could first be detected after 16-18 days p.i. in both groups the amount of antibodies was significantly higher in sera of trout kept at 10-12 degrees C at day 22 and day 28 p.i. than in sera of trout kept at 15-17 degrees C. These results indicate stronger A. salmonicida induced activation of monocytes, granulocytes and B-lymphocytes at higher temperature. However, the development of a specific antibody response against A. salmonicida seemed to be more effective at lower temperatures.     

Effect of turpentine oil on C-reactive protein (CRP) production in rainbow trout (Oncorhynchus mykiss)

The effect of turpentine oil on C-reactive protein (CRP) production was studied in rainbow trout (Oncorhynchus mykiss). Serum CRP concentration was estimated by sandwich enzyme-linked immunosorbent assay using anti-rainbow trout CRP monoclonal antibody (mAb) AC4 and polyclonal antibody. Intracellular CRP was demonstrated by flow cytometry using anti-trout CRP mAb. Hepatocytes, head kidney macrophages, spleen lymphocytes and peripheral blood lymphocytes showed reaction against AC4, but RTG-2 fibroblastic line cells, derived from rainbow trout gonad did not. This is the first report on the detection of intracellular CRP in fish. CRP levels decreased significantly 1 day after intramuscular injection of turpentine oil and remained low for 14 days. Significant decreases in the expression of CRP in hepatocytes, head kidney macrophages and spleen lymphocytes after injection of turpentine oil were found. The reduction of serum CRP concentration after turpentine oil injection may be attributed to decreases in intracellular CRP synthesis.     

Cold acclimation increases basal heart rate but decreases its thermal tolerance in rainbow trout (Oncorhynchus mykiss)

Rainbow trout (Oncorhynchus mykiss, Walbaum) were acclimated to 4 degrees C and 17 degrees C for more than 4 weeks and heart rate was determined in the absence and presence of adrenaline to see how thermal adaptation influences basal heart rate and its beta-adrenergic control in a eurythermal fish species. The basal heart rate in vitro was higher in cold-acclimated than warm-acclimated rainbow trout at temperatures below 17 degrees C. On the other hand, adaptation to cold decreased thermal tolerance of heart rate so that the maximal heart rates were achieved at 17 degrees C (75 +/- 4 bpm) and 24 degrees C (88 +/- 2 bpm) in cold-acclimated and warm-acclimated trout, respectively. Beta-adrenergic response of the heart was enhanced by cold-adaptation, since adrenaline (100 nmol l(-1)) caused stronger stimulation of heart rate in cold-acclimated (29 +/- 14%) than in warm-acclimated fish (10 +/- 1%; P = 0.03). Furthermore, adrenaline strongly opposed the temperature-dependent deterioration of force production in cold-acclimated trout but not in warm-acclimated trout. The results indicate that adaptation to cold increases basal heart rate but decreases its thermal tolerance in rainbow trout. Cold acclimation up-regulates the beta-adrenergic system, and beta-adrenoceptor activation seems to provide cardioprotection against high temperatures in the cold-adapted rainbow trout.     

Muscle insulin binding and plasma levels in relation to liver glucokinase activity,glucose metabolism and dietary carbohydrates in rainbow trout

Rainbow trout were fed for 10 weeks with either a carbohydrate-free diet (C-free) or with four experimental diets containing various levels (20 or 40%) and sources of starch (extruded wheat or peas) in order to examine metabolic utilisation of dietary vegetable carbohydrates and its endocrine control. The study was focused on the parameters described as limiting in glucose metabolism in fish. Feeding trials were conducted at 8 and 18 degrees C to establish whether carbohydrate-rich diets can be used in trout farming irrespective of water temperature. At both temperatures, pea diets (especially the highest level) resulted in a feed efficiency as high as the C-free diet. Fish had similar growth rates except when fed the low wheat content diet. Glycaemia values 6 h after feeding were significantly higher in trout fed carbohydrate diets than those given the C-free diet, whereas plasma insulin levels were similar independently of the levels of dietary starch. This study provides the first evidence that glucokinase (GK) activity and mRNA level in trout liver increase in proportion to the content of dietary starch. Nevertheless, these changes were not correlated with plasma insulin levels. Insulin-like growth factor-I (IGF-I) binding and number of receptors in skeletal muscle were consistently higher than those for insulin but no diet-induced differences were found for any of these parameters. Temperature clearly affected the postprandial profile of glucose and insulin, which both showed lower levels 6 h after feeding at 8 degrees C than at 18 degrees C, which was consistent with a lower feed intake. Glucose and insulin levels decreased markedly 24 h after feeding at 18 degrees C, while they were still high at 8 degrees C, an observation concordant with delayed transit rate. These findings indicate satisfactory adaptation of rainbow trout to diets with a relatively high vegetable starch content, especially when provided as extruded peas, and indicate that diets with increased levels of carbohydrates can be used in this species even when it is reared at low temperature.     

Effect of Gyrodactylus derjavini infections on cortisol production in rainbow trout fry

Cortisol production in fry of rainbow trout (367-456 mg body weight) infected with the ectoparasitic monogenean Gyrodactylus derjavini (mean intensities 4.7 and 4.9 parasites per fish) was studied at two temperature levels, 4-6 degrees C and 11-12 degrees C, respectively. Due to difficulties in obtaining an adequate amount of plasma from the small sized fish, the corticosteroid concentration was measured in the body fluid recovered (as supernatant) after sonication and centrifugation of whole fry. Infected fry at 11-12 degrees C showed an elevated level of cortisol compared to uninfected fry. However, the cortisol concentration was lower than in fish exposed to handling stress. At 4 degrees C, the cortisol level in infected fish compared to uninfected was insignificantly increased. The findings are discussed in relation to the role of monogeneans as inducers of secondary infections.     

Electrophysiological properties of rainbow trout cardiac myocytes in serum-free primary culture

A low-density primary culture of trout ventricular myocytes in serum-free growth medium was established and maintained for up to 10 days at 17 degrees C. The myocytes retained their normal rod shaped morphology, capacitive surface area of the sarcolemma (SL), and contractile quiescence. However, sarcolemmal cation currents changed significantly, some permanently, some transiently, after 8-10 days of culture. TTX-sensitive sodium current (I(Na)) and Ba(2+)-sensitive background inward rectifier potassium current (I(K1)) were permanently depressed to 24-28% of their control density measured in freshly isolated myocytes. In contrast, L-type calcium current (I(Ca)) was only transiently downregulated; after 2-3 days in culture, the density of the current was 32% of the control and recovered to the control value after 8-10 days in culture. The changes in membrane currents were reflected in the shape of the action potential (AP). After 2-3 days in culture, maximal overshoot potential and resting potential were significantly reduced, and the durations of the AP at 50 and 90% repolarization were significantly increased. These changes became significantly more pronounced after 8-10 days of culture, with the exception of AP duration at 50% repolarization level. The shortening of the early plateau phase may reflect an additional change to an outward current, presumably the rapid component of the delayed rectifier (I(Kr)). Although the present findings indicate that fish cardiac myocytes can be maintained in serum-free primary culture for at least 10 days at 17 degrees C, some but not all of the electrophysiological characteristics of the myocytes change markedly during culture. The changes in ion currents were not due to loss of sarcolemmal membrane and therefore are likely to represent altered expression of cation currents as an adaptive response to culture conditions.     

Effects of acid water exposure on plasma cortisol, ion balance, and immune functions in the "cobalt" variant of rainbow trout

This study was undertaken to examine physiological responses to acidification of environmental water in the "cobalt" variant of rainbow trout (Oncorhynchus mykiss), which exhibits malformation of the pituitary, by following changes in plasma levels of cortisol and electrolytes, blood pH, gill Na(+), K(+)-ATPase activity, and immune functions after exposure to acid water (pH 4.5). Resting levels of plasma cortisol and lysozyme were significantly lower in the cobalt variant than in the normal trout, whereas plasma ceruloplasmin was significantly higher in the cobalt variant, suggesting that some endocrine factors, lacking or deficient in the cobalt variant, are important for the regulation of its immune functions. Blood pH was slightly but significantly lower in the cobalt variant at rest. After exposure to acid water for 24 h, both the normal trout and cobalt variant showed a significant elevation in plasma cortisol, although the increased level in the cobalt variant was still lower than that in the normal trout transferred to neutral water. No differences were seen in blood pH, plasma electrolytes, and gill Na(+), K(+)-ATPase activity between the normal trout and the cobalt variant, indicating that the cobalt variant regulates ion balance when exposed to acid water, despite malformation of the pituitary. Although the normal trout showed a reduction in plasma lysozyme level after acid exposure, there was no significant change in the cobalt trout. Adverse effects of pituitary malformation on ion balance and immune functions may be compensated by extrapituitary factors in the cobalt variant when it is exposed to acid water.     

Immunological parameters of Javanese carp Puntius gonionotus (Bleeker) exposed to copper and challenged with Aeromonas hydrophila.

This study was to determine the median lethal concentration (LC50) of copper to Javenese carp, Puntius gonionotus (Bleeker), and the immune response after the fish were exposed to sublethal levels of copper and challenged with formalin killed Aeromonas hydrophila. The LC50 of copper on P. gonionotus at 24, 48, 72, 96 and 120 h were estimated as 2.17, 0.91, 0.57, 0.53 and 0.42 mg l(-1), respectively. To determine the effect of copper on the immune system, fish were exposed for 66 days to 0.05, 0.10 and 0.15 mg Cu l(-1). After 56 days of initial exposure to copper, fish were challenged with 0.1 ml of 4.5 x 10(5) cfu ml(-1) formalin killed A. hydrophila and maintained in the same concentration of copper. After the challenge, the immune response was monitored for 2 weeks using haematological and serological assays. During the initial phase of exposure to copper, significant changes were noted in the white blood cell, lysozyme, potential killing activity, total plasma protein, total immunoglobulin and haematocrit levels between the control and treated fish. One week after challenge with A. hydrophila, there was a significant increase in the values of white blood cells, total protein and total immunoglobulin compared to the values before the challenge. However, these values were not significantly different (P>0.05) between the control and the treated fish. In contrast, NBT and lysozyme assays exhibited a significant difference (P<0.05) in fish exposed to 0.10 mg Cu l(-1) (0.525 +/- 0.17; 24.42 +/- 3.35 x 10(2) micromg ml(-1)) and 0.15 mg Cu 1(-1) (0.536 +/- 0.19; 21.78 +/- 1.29 x 10(2) micromg ml(-1)) compared to the control (0.746 +/- 0.31; 30.73 +/- 5.42 x 10(2) micromg ml(-1)) after the bacterial challenge (day 61). There was however no significant difference (P>0.05) in NBT and lysozyme levels in fish exposed to lower level of copper (0.05 mg Cu l(-1)), suggesting the absence of immunosuppressive effects at lower level of exposure.     

Stress effects on AVT and CRF systems in two strains of rainbow trout (Oncorhynchus mykiss) divergent in stress responsiveness

The aim for this study was to examine whether the F4 generation of two strains of rainbow trout divergent in their plasma cortisol response to confinement stress (HR: high responder or LR: low responder) would also differ in stress-induced effects on forebrain concentrations of mRNA for corticotropin-releasing factor (CRF), arginine vasotocin (AVT), CRF receptor type 1 (CRF-R1), CRF receptor type 2 (CRF-R2) and AVT receptor (AVT-R). In addition, plasma cortisol concentrations, brainstem levels of monoamines and monoamine metabolites, and behaviour during confinement were monitored. The results confirm that HR and LR trout differ in their cortisol response to confinement and show that fish of these strains also differ in their behavioural response to confinement. The HR trout displayed significantly higher locomotor activity while in confinement than LR trout. Moreover, following 180 min of confinement HR fish showed significantly higher forebrain concentrations of CRF mRNA than LR fish. Also, when subjected to 30 min of confinement HR fish showed significantly lower CRF-R2 mRNA concentrations than LR fish, whereas there were no differences in CRF-R1, AVT or AVT-R mRNA expression between LR and HR fish either at 30 or 180 min of confinement. Differences in the expression of CRF and CRF-R2 mRNA may be related to the divergence in stress coping displayed by these rainbow trout strains.     

Bioelectronic monitoring of parasite-induced stress in brown trout and roach

A non-contact bioelectronic monitoring system was used to record changes in heart rate, ventilation rate and swimming activity in brown trout Salmo trutta and roach Rutilus rutilus , following exposure to two species of cercariae of digenean trematodes: Diplostomum pseudospathaceum which is a common parasite in the lens of fishes and xiphidiocercariae of Plagiorchis elegans , a parasite of anatid birds, both of which have the snail Lymnaea stagnalis as their first intermediate host. Swimming activity increased significantly in roach exposed to Diplostomum cercariae at densities as low as 3.8l⁻¹ and remained elevated for 24–36 h post exposure. Brown trout showed no response when exposed to low densities of Diplostomum (2.9 and 5.7 cercariae 1⁻¹) but there was a significant response at higher cercarial exposure densities (>501⁻¹). Total activity of brown trout increased immediately, peaking after 2 h and returning to pre-exposure levels within 5–6 h. There was a simultaneous increase in heart and ventilation rates which both declined following the reduction in activity of the fish. Heart rate then increased for a second time to a maximum level at 14–16 h and thereafter declined to reach a steady state at 3 days post-exposure. During this period there was no significant change in total activity. The qualitative nature of the heart response was identical in five infected brown trout although the magnitude of the response varied widely among fish. Exposure to cercariae of P. elegans elicited no response in either fish species. (c) 1996 The Fisheries Society of the British Isles     

Exhaustive exercise does not affect the preferred temperature for recovery in juvenile rainbow trout (Oncorhynchus mykiss)

We tested the hypothesis that juvenile rainbow trout (Oncorhynchus mykiss) would select a temperature colder than their acclimation temperature (16 deg +/-1 deg C) to minimize postexhaustive exercise metabolic demands and enhance oxygen availability. After an initial 3-h exploratory period in a thermal gradient (6 degrees -25 degrees C), fish selected a temperature of approximately 14 degrees C and had a baseline exploratory swimming activity of approximately 60 cm min(-1). Subsequently, experimental (chased) fish were individually removed, exhaustively exercised for 1.5 min, and replaced. Both control (unchased) and experimental fish were allowed to explore the thermal gradient for another 2 h. Immediately after being chased, trout had a metabolic profile that was consistent with being exhausted; levels of plasma and muscle lactate were 4.38+/-0.25 mmol L(-1) and 28.0+/-2.0 mmol kg(-1), respectively, and levels of muscle glycogen, adenosine triphosphate, and phosphocreatine were 3.89+/-0.95, 4.23+/-0.62, and 3.07+/-0.73 mmol kg(-1), respectively. Although exploratory swimming activity of the chased fish was significantly lower (by 81%) as compared with control fish during the first 5 min postchase, differences in the mean, median, and mode values for selected temperatures during the next 2 h were neither large (<1 degrees C) nor significant (P>0.05). Contrary to our initial hypothesis, these findings suggest that juvenile rainbow trout do not select a colder temperature to decrease metabolic rate following exhaustive exercise. Instead, rainbow trout selected a temperature marginally cooler than their acclimation temperature (16 degrees C) regardless of whether they had been previously exhausted.     

Toxicological stress response and cadmium distribution in hybrid tilapia (Oreochromis sp.) upon cadmium exposure

Adult tilapia were exposed to 0 (control) and 4.45 microM Cd for 0 h, 5 h, 5 days, and 15 days, and the physiological responses of fish were described. The physiological responses were first expressed in gill tissue, in which mucus cells secretion increased, Cd accumulated, cortisol secretion was significantly higher, but serum ACH(50) activity (alternative complement hemolytic assay) was significantly lower than in controlled fish. After 5 days of Cd exposure, the ACH(50) activity showed a greater decrease, but lysozyme and cortisol contents showed significant increases over the control. Cd levels significantly increased in intestines, liver, and kidneys, and a significant induction of metallothionein (MT) protein in hepatic tissue was noted. Finally, the Cd accumulation rate still showed significant increases in these organs. However, the MT content was similar at 5 days and at 15 days after Cd exposure, and the cortisol contents had recovered to the pre-exposure level. In addition, Cd accumulation in muscle was higher after Cd exposure than in controls (t-test, p<0.05). Our results demonstrate (1) that tilapia readily regulate their physiological parameters in order to acclimate to a sublethal Cd environment; (2) these changes of physiological parameters may be related with a succession of cortisol levels following Cd exposure; (3) increasing rate of hepatic MT contents and Cd accumulation rate didn't appear identical after 5-15 days of Cd exposure. This was confirmed that hepatic MT was not a good indicator for Cd levels in tilapia.     

The effects of short-term acute cadmium exposure on blue tilapia,Oreochromis aureus

Synopsis Disease-free blue tilapia,Oreochromis aureus, exposed to cadmium (0.5 ppm and 10 ppm) showed very significant and dramatic decrease in food consumptions. Food consumptions returned to near normal 21 days after fish were returned to cadmium-free water. Along with anorexia there were decreases in body weights during the period when fish were exposed to cadmium. Fish in cadmium-free water that were pair-fed to cadmium-exposed fish (0.5 ppm) did not gain weight but there were no decreases in body weights. Cadmium was still in tissues 34 days after the fish were placed in cadmium-free water and the accumulation was highest in the kidney; this was followed by liver, brain, gill filaments and muscles. The accumulations of the heavy metal (in kidneys and gills) were significantly higher in fish exposed to high than low cadmium levels. There were no differences in complement levels (haemolytic acitivity) in cadmium-exposed and cadmium-free fish. However, cadmium-exposed fish did not produce detectable haemagglutinating antibodies against sheep red blood cells while cadmium-free fish responded well to the antigen. The anorexia in cadmium-exposed fish contributed to the depression in antibody production.     

食物相铬在豹纹鳃棘鲈鱼不同脑区的生物累积

为研究食物来源的铬(Cr)在鱼脑部生物累积的情况, 用含有不同浓度(0、10、50和250 mg/kg)不同形态及价态Cr[有机Cr为吡啶甲酸铬Cr Pic, 无机Cr为Cr Cl₃和K₂Cr₂O₇(Cr(Ⅲ); Cr(Ⅵ)]的饲料投喂豹纹鳃棘鲈(Plectropomus. leopardus)幼鱼66d, 并以原子吸收光谱法(AAS)在第7、第12、第18、第40和第66天取样测定幼鱼的下丘脑、前脑、中脑和后脑区域中Cr生物累积量。结果表明, 食物中铬在幼鱼4种脑组织中的累积量普遍在暴露前期(7—40d)显著增加, 而在最后一个时期(66d)显著减少。但是, 总铬的生物蓄积量在4种脑区并未以剂量和时间依赖性方式存在。此外, 在相同浓度和时间条件下, 不同铬源Cr Pic、Cr(Ⅲ)和Cr(Ⅵ)的处理,总铬在不同脑区的含量基本呈现Cr Pic > Cr(Ⅲ) > Cr(Ⅲ)的规律, 具有明显的组织差异性。研究发现食物来源的Cr在鱼类等水生动物大脑不同脑区的累积与Cr不同形态、价态和浓度紧...     

Waterborne vs. dietary copper uptake in rainbow trout and the effects of previous waterborne copper exposure

Juvenile rainbow trout (Oncorhynchus mykiss) were exposed to waterborne Cu (22 microg/l) in moderately hard water for up to 28 days. Relative to control fish kept at background Cu levels (2 microg/l), Cu-preexposed fish displayed decreased uptake rates of waterborne Cu via the gills but not of dietary Cu via the gut during 48-h exposures to (64)Cu-radiolabeled water and diet, respectively. At normal dietary and waterborne Cu levels, the uptake rates of dietary Cu into the whole body without the gut were 0.40-0.90 ng. g(-1). h(-1), >10-fold higher than uptake rates of waterborne Cu into the whole body without the gills, which were 0.02-0.07 ng. g(-1). h(-1). Previously Cu-exposed fish showed decreased new Cu accumulation in the gills, liver, and carcass during waterborne (64)Cu exposures and in the liver during dietary (64)Cu exposures. A 3-h gill Cu-binding assay showed downregulation of the putative high-affinity, low-capacity Cu transporters and upregulation of the low-affinity, high-capacity Cu transporters at the gills in Cu-preexposed fish. Exchangeable Cu pools in all the tissues were higher during dietary than during waterborne (64)Cu exposures, and previous Cu exposure reduced waterborne exchangeable Cu pools in gill, liver, and carcass. Overall, these results suggest a quantitatively greater role for the dietary than for the waterborne route of Cu uptake, a key role for the gill in Cu homeostasis, and important roles for the liver and gut in the normal metabolism of Cu in fish.