Dietary plant-protein substitution affects hepatic metabolism in rainbow trout (Oncorhynchus mykiss)

The high dietary protein requirements of salmonid fish are met with fishmeal-based feed in commercial aquaculture. The sustainability of this practice is questionable and, therefore, the feasibility of substituting fishmeal with plant-based products needs to be investigated. We investigated growth and metabolism in rainbow trout (Oncorhynchus mykiss) fed a diet composed of a mixture of plant proteins compared with those fed a fishmeal-based diet. Using two-dimensional gel electrophoresis of liver protein extracts, we showed that the liver protein profile changed in response to the alteration in the diet. A number of metabolic pathways were identified as sensitive to the protein source substitution. These included pathways involved in primary energy generation, maintenance of reducing potential, bile acid synthesis, and transport and cellular protein degradation. Interestingly, the pathways shown to be affected in the present study were somewhat different from those identified in our previous work with soyabean-based-protein replacement of fishmeal, with the effects on the abundance of several stress response proteins notably absent. We conclude, therefore, that the metabolic effects of plant protein replacement in aquaculture feed varies with plant-protein source.     

Dietary low-glucosinolate rapeseed meal affects thyroid status and nutrient utilization in rainbow trout (Oncorhynchus mykiss)

Two rapeseed (Brassica napus) meals, RM1 and RM2, with two levels of glucosinolates (GLS; 5 and 41 mumol/g DM respectively) were incorporated at the levels of 300 and 500 g/kg of the diets of juvenile rainbow trout (Oncorhynchus mykiss) in replacement of fish meal, and compared with a fish-meal-based diet. A decrease in the digestibility of the DM, protein, gross energy and P was observed with high-rapeseed meal (RM) incorporation. In trout fed on RM-based diets, growth performance was reduced even after only 3 weeks of feeding. Feed efficiency was adversely affected by RM and GLS intake. Protein and energy retention coefficients were significantly lower in fish fed on the diet containing the higher level of GLS. P retention was significantly lower with all the RM-based diets than with the fish-meal diet. Irrespective of the degree of growth inhibition, fish fed on RM-based diets exhibited similar typical features of hypothyroid condition due to GLS intake, expressed by lower plasma levels of triiodothyronine and especially thyroxine and a hyperactivity of the thyroid follicles. This hypothyroidal condition led to a strong adjustment of the deiodinase activities in the liver, the kidney and the brain. A significant increase of the outer ring deiodinase activities (deiodinases type I and II respectively) and a decrease of the inner ring deiodinase activity (deiodinase type III) were observed. It is concluded that the observed growth depression could be attributed to the concomitant presence of GLS, depressing the thyroid function, and of other antinutritional factors affecting digestibility and the metabolic utilization of dietary nutrients and energy.     

Plasma vitellogenin levels in pre-spawning rainbow trout,Oncorhynchus mykiss,during acid exposure

Vitellogenic rainbow trout (Oncorhynchus mykiss were exposed to pH 7.6, 5.6, and 4.5 for 20 days. Plasma vitellogenin (Vg) which is an indicator of the level of exogenous yolk precursors synthesized in the liver, and transported to the ovary was measured in sexually maturing females using a sensitive homologous radioimmunoassay specific for rainbow trout. During the September–October experiments, Vg levels significantly increased at pH 7.6 and 5.6 over the 20-day exposure period. At pH 4.5, however, Vg levels did not change during the experimental period. Based on differences between day 0 and 20 plasma Vg levels, females at pH 7.6, 5.6, and 4.5 produced 0.357, 0.188 and 0.084 mg/ml/day Vg, respectively. The use of this sensitive homologous radioimmunoassay has confirmed the effect upon the reproductive mechanism of vitellogenesis at pH 4.5. Lower levels of this important yolk source in the oocyte could alter the successful development of the embryo during later stages of development.     

Influence of dietary sodium on waterborne copper toxicity in rainbow trout,Oncorhynchus mykiss

Juvenile rainbow trout were fed diets containing control (0.26 mmol/g) or elevated (1.3 mmol/g) dietary Na+ in combination with either background (19 nmol/L) or moderately elevated levels (55 or 118 nmol/L) of waterborne Cu for 21 d. Unidirectional waterborne Na+ uptake rates (measured with 22Na) were up to four orders of magnitude higher than those of Cu (measured with 64Cu). Chronic exposure to elevated dietary Na+ alone or in combination with elevated waterborne Cu decreased whole-body uptake rates of waterborne Na+ and Cu. Accumulation of new Cu and Na+ at the gills was positively and highly significantly correlated and responded to the experimental treatments in a similar fashion, suggesting that Na+ and Cu have common branchial uptake pathways and that dietary Na+ preexposure modifies these pathways. Chronic exposure to elevated waterborne Cu significantly increased Cu concentrations in the liver but caused only modest increases in total Cu concentrations in the whole body and gill. Chronic exposure to elevated dietary Na+ slightly decreased whole-body Cu concentration on day 14 and greatly reduced liver Cu concentration on days 14 and 21; new Cu accumulation in whole-body, gill, and internal organs was reduced on all days. Chronic exposure to elevated waterborne Cu or dietary Na+ alone reduced short-term gill Cu binding at low waterborne Cu concentrations. At high waterborne Cu concentrations, chronic exposure to elevated waterborne Cu had no effect, while elevated dietary Na+ increased Cu binding to the gills. Combined chronic exposure to elevated dietary Na+ and waterborne Cu decreased gill Cu binding over the entire range of Cu concentrations tested. Clearly, chronic exposure to elevated dietary Na+ and waterborne Cu appears to modify gill Cu-binding characteristics and may be important considerations in future development of a chronic biotic ligand model for Cu.     

Metal-metal interactions of dietary cadmium, copper and zinc in rainbow trout, Oncorhynchus mykiss

The influence of metal-metal interactions on uptake, accumulation, plasma transport and chronic toxicity of dietary Cu, Cd and Zn in rainbow trout (Oncorhynchus mykiss) was explored. Juvenile rainbow trout were fed diets supplemented with (μg/g) 500 Cu, 1000 Zn and 500 Cd singly and as a ternary mixture at 2.5% body weight daily ration for 28 days. Complex interactions among the metals dependent on the tissue/organ, metals ratios and duration of exposure were observed. While Zn did not accumulate, whole-body Cd and Cu concentrations increased following linear and saturation patterns, respectively. Early enhanced whole-body Cu accumulation in fish exposed to the metals mixture was correlated with reduced Cd concentration whereas late enhancement of Cd accumulation corresponded with elevated Cd concentration. This suggests early mutual antagonism and late cooperation between Cd and Cu probably due to interactions at temporally variable metal accumulation sites. At the level of uptake, Cd and Cu were either antagonistic or mutually increased the concentrations of each other depending on the duration of exposure and section of the gut. At the level of transport, enhanced Cd accumulation in plasma was closely correlated with reduced concentrations of both Zn and Cu indicating competitive binding to plasma proteins and/or antagonism at uptake sites. Compared to the Cu alone exposure, Cu concentrations were either lower (gills and carcasses) or higher (liver and kidney) in fish exposed to the metals mixture. On the other hand, Cd accumulation was enhanced in livers and carcasses of fish exposed to the mixture compared to those exposed to Cd alone, while Zn stimulated Cu accumulation in gills. Chronic toxicity was demonstrated by elevated malondialdehyde levels in livers and reduced concentrations of Zn and Cu in plasma. Overall, interactions of Cd, Cu and Zn are not always consistent with the isomorphous competitive binding theory.     

Social interactions affect physiological consequences of sublethal copper exposure in rainbow trout,Oncorhynchus mykiss

The interactions of sublethal waterborne copper exposure and social dominance behavior were examined in juvenile rainbow trout. Dominance hierarchies were determined between pairs of fish by behavioral observations and among groups of 10 fish by the use of passive integrated transponder (PIT) tagging equipment. The present study is one of the first to utilize this novel PIT tag method for behavioral assessment. Feeding behavior was quantified by placing a PIT tag recorder at the entrance to the feeding area. Linear dominance hierarchies were documented based on these observations of feeding behavior. Dominance hierarchies established in control water were not altered by exposure to 30 microg/L of copper; however, physiological responses of fish to sublethal concentrations of copper were related to social rank. Subordinate fish exhibited a higher accumulation of copper in both gill and liver tissue. Subordinates of paired fish were also shown to have a higher uptake of sodium than dominant fish, and the uptake of sodium was correlated with uptake of copper from the water. Therefore, within a population of fish, it cannot be assumed that individuals of different social status will exhibit the same physiological responses to the presence of copper.     

Effects of subchronic nitrite exposure on rainbow trout (Oncorhynchus mykiss)

Subchronic toxicity of nitrite in rainbow trout (Oncorhynchus mykiss; mean mass±S.D., 18.9±1.3 g) was assessed in a 28-day trial. The influence of nitrite on fish mortality, growth rate, haematology, blood biochemistry, and gill histology was observed. Survival was not affected by exposures up to 1 mg l⁻¹ NO₂⁻ (at 10 mg l⁻¹ Cl⁻). On the basis of growth rate inhibition data, the values of NOEC (28 d LC₀) and LOEC (28 d LC₁₀) were estimated at 0.01 and 0.2 mg l⁻¹ NO₂⁻, respectively. At 0.01 mg l⁻¹ NO₂⁻ (the lowest concentration tested), there was segmental hyperplasia of the respiratory epithelium of secondary lamellae and elevated glucose and decreased potassium. Elevated nitrite concentrations were found in blood plasma of fish exposed to concentrations of 1.0 mg l⁻¹ NO₂⁻ and higher, and in muscle tissue at the highest concentration 3.0 mg l⁻¹ NO₂⁻. Plasma and muscle nitrite levels were lower than those in the ambient water in all experimental groups.     

Dietary accumulation of perfluorinated acids in juvenile rainbow trout (Oncorhynchus mykiss)

Perfluorinated acids (PFAs) recently have emerged as persistent global contaminants after their detection in wildlife and humans from various geographic locations. The highest concentrations of perfluorooctane sulfonate are characteristically observed in high trophic level organisms, indicating that PFAs may have a significant bioaccumulation potential. To examine this phenomenon quantitatively, we exposed juvenile rainbow trout (Oncorhynchus mykiss) simultaneously to a homologous series of perfluoroalkyl carboxylates and sulfonates for 34 d in the diet, followed by a 41-d depuration period. Carcass and liver concentrations were determined by using liquid chromatography-tandem mass spectrometry, and kinetic rates were calculated to determine compound-specific bioaccumulation parameters. Depuration rate constants ranged from 0.02 to 0.23/d, and decreased as the length of the fluorinated chain increased. Assimilation efficiency was greater than 50% for all test compounds, indicating efficient absorption from food. Bioaccumulation factors (BAFs) ranged from 0.038 to 1.0 and increased with length of the perfluorinated chain; however, BAFs were not statistically greater than 1 for any PFA. Sulfonates bioaccumulated to a greater extent than carboxylates of equivalent perfluoroalkyl chain length, indicating that hydrophobicity is not the sole determinant of PFA accumulation potential and that the acid function must be considered. Dietary exposure will not result in biomagnification of PFAs in juvenile trout, but extrapolation of these bioaccumulation parameters to larger fish and homeothermic organisms should not be performed.     

Altering cytochrome P4501A activity affects polycyclic aromatic hydrocarbon metabolism and toxicity in rainbow trout (Oncorhynchus mykiss)

The polycyclic aromatic hydrocarbons (PAHs) phenanthrene and retene (7-isopropyl-1-methyl phenanthrene) are lethal to rainbow trout (Oncorhynchus mykiss) larvae during chronic exposures. Phenanthrene is a low-toxicity, non-cytochrome P4501A (CYP1A)-inducing compound that accumulates in fish tissues during exposure to lethal concentrations in water. Retene is a higher toxicity CYP1A-inducing compound that is not detectable in tissue at lethal exposure concentrations. The metabolism, excretion, and toxicity of retene and phenanthrene were examined in juvenile and larval rainbow trout during coexposure to the model CYP1A inducer beta-naphthoflavone (betaNF), or to the inducer-inhibitor piperonyl butoxide to determine if modulating CYP1A activity affected PAH metabolism and toxicity. Phenanthrene metabolism, excretion rate, and toxicity increased with coexposure to betaNE Piperonyl butoxide inhibited phenanthrene metabolism and reduced the excretion of all phenanthrene metabolites. As a consequence, embryo mortality rates increased but rates of sublethal effects did not. Coexposure of trout to retene and betaNF caused no change in retene metabolism and excretion, but retene toxicity increased, perhaps due to additivity. Piperonyl butoxide inhibited retene metabolism, decreased the excretion of some retene metabolites while increasing the excretion of others, and increased the toxicity of retene. These results support the role of CYP1A activity in PAH metabolism and excretion, and the role ofthe CYP1A-generatedmetabolites of PAHs in chronic toxicity to larval fish.     

Effects of sublethal concentrations of triphenyltinacetate on rainbow trout (Oncorhynchus mykiss)

To evaluate the toxic effects of sublethal concentrations of the fungicide triphenyltinacetate (TPTAc), a prolonged toxicity study was made on rainbow trout (Oncorhynchus mykiss). Fish were exposed to TPTAc concentrations ranging from 1 to 6 g TPTAc/L for 28 and 18 days, respectively, using a flow-through exposure system. Hematological findings included an increase of the total number of erythrocytes and an elevated incidence of erythrocyte degradation stages at 4 g TPTAc/L and higher. The hemoglobin content and the packed-cell volume increased as well at 4 and 1 g TPTAc/L. Whereas the total number of leucocytes increased in fish exposed to 1 g TPTAc/L, the number of leucocytes tended to decrease at higher concentrations. The percentage of lymphocytes within the differential blood cell count decreased. The histopathological examination of TPTAc-exposed fish showed a dose-related lymphocytic depletion of the spleen, accompanied by a proliferation of reticuloendothelial cells and an increased erythrophagia even at the lowest TPTAc concentration. In severe cases, cell necrosis was evident. In liver tissue, a depletion of the glycogen deposits within the hepatocytes could be detected in fish exposed to 4 and 6 g TPTAc/L. The analysis of the phenyltin compounds within various organs of fish by HRGC-FPD revealed remarkable concentrations of triphenyltin of up to 16.1 g/g with the following order of residue levels: liver > kidney > spleen > gills > muscle. Di- and monophenyltin were found only in traces of 1–109 ng/g in these organs. The present study indicates that TPTAc negatively affects rainbow trout in a concentration range that might be present in aquatic environments.     

Dynamics of 17alpha-ethynylestradiol exposure in rainbow trout (Oncorhynchus mykiss): absorption, tissue distribution, and hepatic gene expression pattern

17alpha-Ethynylestradiol (EE2) is a synthetic estrogen identified in sewage effluents. To understand better the absorption kinetics of EE2 and the induction of vitellogenin (VTG) and estrogen receptor alpha (ERalpha) mRNA, we subjected male rainbow trout (Onchorynchus mykiss) to continuous water exposures of 125 ng/L of EE2 for up to 61 d. Trout were either repetitively sampled for blood plasma or serially killed at selected time intervals. Vitellogenin, ERalpha mRNA, and EE2 were measured using enzyme-linked immunosorbent assay and using quantitative polymerase chain reaction and gas chromatography-mass spectrometry, respectively. In separate experiments, trout were exposed to EE2 for 7 d, and hepatic gene expression was assessed using a low- and high-density cDNA microarray. The EE2 was rapidly absorbed by the trout, with an apparent equilibrium at 16 h in plasma and liver. The ERalpha mRNA levels also increased rapidly, reaching near-peak levels by 48 h. In contrast, plasma levels of VTG continuously increased for 19 d. After 61 d, tissues with the highest levels of VTG were the liver, kidney, and testes. Microarray-based gene expression studies provided unexpected results. In some cases, known estrogen-responsive genes (e.g., ERalpha) were unresponsive, whereas many of the genes that have no apparent link to estrogen function or EE2 toxicity were significantly altered in expression. Of the two microarray approaches tested in the present study, the high-density array appeared to be superior because of the improved quality of the hybridization signal and the robustness of the response in terms of the number of genes identified as being EE2 responsive.     

Acute and chronic toxicity of nickel to rainbow trout (Oncorhynchus mykiss)

Of the fish species tested in chronic Ni exposures, rainbow trout (Oncorhynchus mykiss) is the most sensitive. To develop additional Ni toxicity data and to investigate the toxic mode of action for Ni, we conducted acute (96-h) and chronic (85-d early life-stage) flow-through studies using rainbow trout. In addition to standard toxicological endpoints, we investigated the effects of Ni on ionoregulatory physiology (Na, Ca, and Mg). The acute median lethal concentration for Ni was 20.8 mg/L, and the 24-h gill median lethal accumulation was 666 nmol/g wet weight. No effects on plasma Ca, Mg, or Na were observed during acute exposure. In the chronic study, no significant effects on embryo survival, swim-up, hatching, or fingerling survival or growth were observed at dissolved Ni concentrations up to 466 microg/L, the highest concentration tested. This concentration is considerably higher than the only other reported chronic no-observed-effect concentration (<33 microg/L) for rainbow trout. Accumulation of Ni in trout eggs indicates the chorion is only a partial barrier with 36%, 63%, and 1% of total accumulated Ni associated with the chorion, yolk, and embryo, respectively. Whole-egg ion concentrations were reduced by Ni exposure. However, most of this reduction occurred in the chorion rather than in the embryos, and no effects on hatching success or larval survival were observed as a result. Plasma ion concentrations measured in swim-up fingerlings at the end of the chronic-exposure period were not significantly reduced by exposure to Ni. Nickel accumulated on the gill in an exponential manner but plateaued in trout plasma at waterborne Ni concentrations of 118 microg/L or greater. Consistent with previous studies, Ni did not appear to disrupt ionoregulation in acute exposures of rainbow trout. Our results also suggest that Ni is not an ionoregulatory toxicant in long-term exposures, but the lack of effects in the highest Ni treatment precludes a definitive conclusion.     

Toxicokinetics of three polychlorinated biphenyl technical mixtures in rainbow trout (Oncorhynchus mykiss)

Accumulation and depuration parameters of polychlorinated biphenyls (PCBs) in fish have been reported only for a few congeners. As well, there is little information on the ability of fish to biotransform PCBs. To address these issues, juvenile rainbow trout (Oncorhynchus mykiss) were exposed to dietary concentrations of three Aroclor mixtures (1248, 1254, 1260) in food for 30 d followed by an additional 160 d of nonspiked food at 8 degrees C. Accumulation, depuration, and potential biotransformation of 92 PCB congeners were assessed. Half-lives (t1/2) of PCB congeners ranged from 79 to 182 d, assimilation efficiencies ranged from 40 to 50% and biomagnification factors (BMF) ranged from 2.9 to 6.9. No evidence of significant biotransformation of any PCB congeners was found. All 92 congeners fell on the same t1/2 to Kow relationship as 16 preselected PCB congeners previously shown to persist in fish and no hydroxylated PCB metabolites (OH-PCBs) were detected in the plasma after 30 d of exposure. These findings suggest that OH-PCBs observed in feral fish may be accumulated from sources other than internal metabolism of the parent congeners, at least for juvenile fish at cool temperatures. Because t1/2s in this experiment were slower than t1/2s reported in other work, water temperature also may be an important factor in determining the t1/2s of all PCB congeners in fish.     

Bioconcentration and tissue distribution of perfluorinated acids in rainbow trout (Oncorhynchus mykiss)

Rainbow trout (Oncorhynchus mykiss) were exposed simultaneously to a homologous series of perfluoroalkyl carboxylates and sulfonates in a flow-through system to determine compound-specific tissue distribution and bioconcentration parameters for perfluorinated acids (PFAs). In general, PFAs accumulated to the greatest extent in blood > kidney > liver > gall bladder. Carboxylates and sulfonates with perfluoroalkyl chain lengths shorter than seven and six carbons, respectively, could not be detected in most tissues and were considered to have insignificant bioconcentration factors (BCFs). For detectable PFAs, carcass BCFs increased with increasing length of the perfluoroalkyl chain, ranging from 4.0 to 23,000, based on wet weight concentrations. Carboxylate carcass BCFs increased by a factor of eight for each additional carbon in the perfluoroalkyl chain between 8 and 12 carbons, but this relationship deviated from linearity for the longest PFA tested, possibly because of decreased gill permeability. In general, half-lives (3.9-28 d) and uptake rates (0.053-1.700 L/kg/d) also increased with increasing length of the perfluoroalkyl chain in all tissues. Sulfonates had greater BCFs, half-lives, and rates of uptake than the corresponding carboxylate of equal perfluoroalkyl chain length, indicating that hydrophobicity, as predicted by the critical micelle concentration, is not the only determinant of PFA bioaccumulation potential and that the acid function must be considered.     

Short-term modulation of lipogenesis by macronutrients in rainbow trout (Oncorhynchus mykiss) hepatocytes

Rainbow trout (Oncorhynchus mykiss) hepatocytes were cultured under simulated conditions of varying nutritional status to explore the short-term modulation by dietary substrates of the main lipogenic enzymes: glucose-6-phosphate dehydrogenase (G6PD), malic enzyme (ME), ATP-citrate lyase (ACL), acetyl-CoA carboxylase (ACoAC) and fatty acid synthetase (FAS). Primary cultures were individually exposed to varying amounts of glucose, hydrolysed casein and long-chain polyunsaturated fatty acids (PUFA) for 12 h. A second set of experiments was designed to evaluate the effects of mixing different relative amounts of these macronutrients in the culture medium. Glucose concentrations of up to 20-25 mm showed a stimulatory effect on G6PD, ME, ACL and ACoAC activity while an earlier inhibitory effect on FAS was observed at 10-20 mm glucose The use of hydrolysed casein as a nutritional source of amino acids inhibited the activity of FAS and ME and stimulated G6PD, ACoAC and ACL activity Low levels of linolenic acid exerted a stimulatory effect on all the lipogenic enzymes assayed with the exception of FAS, and increased amounts showed some inhibition of lipogenic activities Eicosapentaenoic acid and docosahexaenoic acid showed a similar effect, although the former strongly inhibited FAS activity while the latter showed greater potential to inhibit ACoAC and G6PD. A complete change in the relative levels of glucose, hydrolysed casein and PUFA in turn led to changes in the enzyme activity patterns observed. The present study shows the feasibility of exploring the direct regulation of lipogenesis in isolated fish cells by varying the relative amounts of main macronutrients, mimicking in vivo dietary conditions. It is felt that such an approach may serve to investigate the macronutrient regulation of other metabolic pathways.     

Adding magnesium to the silver-gill binding model for rainbow trout (Oncorhynchus mykiss)

Rainbow trout (Oncorhynchus mykiss; 2-17 g) were exposed to approximately 0.1 microM silver as AgNO3 for 3 to 4 h in synthetic, ion-poor water (20 microM Ca, 100 microM Na, 150 microM Cl, pH 7) to which was added Mg, Ca, or thiosulfate (S2O3). Gills were extracted and assayed for Ag using graphite furnace atomic absorption spectrophotometry. Up to 210 mM Mg (fourfold the concentration of Mg in seawater) did not reduce accumulation of Ag by trout gills. The conditional equilibrium stability constant (K) for Mg at silver-binding sites on the gills was calculated to be log K(Mg-gillAg) = 3.0, or approximately half-as-strong binding as for Ca at these sites. The inclusion of the Mg-gill stability constant into the original Ag-gill binding model increases the flexibility of the model, although the competitive effects of Mg are only important in sodium-poor systems.     

Early onset of embryonic mortality in sub-fertile families of rainbow trout (Oncorhynchus mykiss)

Survival during early embryonic development is highly variable in oviparous fishes and appears to be related to events associated with the female at the time of ovulation and spawning. The goal of this study was to identify critical periods of mortality associated with early embryonic development in egg batches from female rainbow trout (Oncorhynchus mykiss) that were checked for ovulation every 5-7 days. The experiment was designed to specifically remove post-ovulatory ageing and reduce paternal variability. Embryo viability in 269 single-pair-mated families was systematically tracked at the following five stages: second cleavage (0.5 days post fertilisation (dpf)), elevated blastula (2.5 dpf), embryonic shield (6 dpf), embryonic keel (9 dpf), and retinal pigmentation (19 dpf). At each of the five stages families with embryo viability assessments of <80% were classed as sub-fertile, whereas those with >80% embryo viability were classed as fertile. Embryo viability in sub-fertile families was distinctly reduced at 0.5 dpf, in contrast to fertile families, but remained constant from that point through to 19 dpf. These results suggest that the critical period of early embryonic mortality in sub-fertile families of rainbow trout parallels events that occur at or shortly after fertilisation and is independent of post-ovulatory aging.     

Morphological effects of acute and chronic atrazine exposure in rainbow trout (Oncorhynchus mykiss)

The effects of the herbicide atrazine (2-Chlor-4-ethyl-amino-6-isopropyl-amino-s-triazine) on the kidney of rainbow trout (Oncorhynchus mykiss) were studied by exposing them to sublethal concentrations of 1.4 and 2.8 mg atrazine per liter of water for 96 h (acute exposure) respectively to 5, 10, 20, 40, and 80 g/L for a period of 28 days (chronic exposure).Alterations of the different components of renal corpuscles and of renal tubules, as well as an increase in cells with mitotic figures in renal hemopoietic interstitium were constant features at lower chronic (5, 10, 20, 40 g/L) exposure; necrosis of endothelial cells and renal hemopoietic tissue were prominent at concentrations of 80 g/L, and 1.4 and 2.8 mg/L atrazine.