Endosulfan effects on muscle malate dehydrogenase of the freshwater catfish Clarias batrachus

Detecting Aquatic Pollution Using Histological Investigations of the Gills, Liver, Kidney, and Muscles of Oreochromis niloticus

The present study aimed to determine the degree of changes in the histological architecture of the liver, gills, kidneys, and muscles of fish Oreochromis niloticus collected from different polluted river sites. Fish samples collected from the Faisalabad Fish Hatchery and upstream of Chakbandi drain acted as a control. Necrosis, hemorrhage, and epithelial hyperplasia were observed in the gills of fish inhabiting the river downstream of the Chakbandi drain entrance. Liver tissues were found to be affected by vacuolated cytoplasm, bile duct proliferation, melanomacrophages, and necrosis. In kidney tissues, shrinkage of the renal cortex, necrosis, and destructive renal tubules were observed. Histopathology of muscles indicates the presence of hypertrophy and swollen myofibers. In contrast, upstream specimens of fish exhibited mild tissue alterations. Histopathology of gills tissue showed vacuolization. Liver tissues indicated the presence of hypertrophy and more frequent Kupffer cells than usual. The vacuolation was also observed in kidney tissues. Muscle tissues expressed splitting of muscle fibres and degeneration in muscle bundles. However, sections of tissues collected from farmed fish have normal morphology and no anomalies. The histopathological assessment indicated various cellular, biochemical, and histological changes in response to the contamination in the vicinity of the fish.

Ecotoxicological Studies on the Action of Actara 25 WG Insecticide on Prussian Carp (Carassius gibelio) and Marsh Frog (Pelophylax ridibundus)

The toxic action of the Actara 25 WG insecticide (it contains 25% thiamethoxam as an active substance) in non-lethal doses was studied in two species of aquatic organisms—the Prussian carp (Carassius gibelio) and the marsh frog (Pelophylax ridibundus)—at two thermal levels, 6–8 °C (low temperature) and 18–20 °C (room temperature), respectively. In the Prussian carp, we recorded decreases in oxygen consumption and stimulation of the respiratory rhythm, changes that were more pronounced in the case of intoxicated fish and when the species were kept at room temperature. The histopathology of the lung in the frog illustrated the thickening of the conjunctival septum, an increase in the number of mucous cells, and an increase in the ratio between the diameter of the nucleus and the diameter of the pneumocyte. All of these changes were more pronounced in the animals kept at higher temperature. Our study looks at the extent to which temperature changes can influence the ability of poikilothermic organisms to withstand the presence of toxic substances in the environment as a result of the impact of the use of insecticides in agriculture. The two tested organisms are a common presence for the study area, which was affected in the last decade by climate change.

Biomarkers for assessing chronic toxicity of carbamazepine, an anticonvulsants drug on Pangasianodon hypophthalmus (Sauvage, 1878)

In recent times, carbamazepine (CBZ) as an anticonvulsants drug has raised attention because of its safety concern in the aquatic environment. The present study aimed to evaluate the sub-lethal effects of CBZ (1%, 0.1 % and 0.01 % of 96 h LC₅₀) on P. hypophthalmus for 60 days based on haematological, biochemical, and genotoxicity biomarkers. Chronic exposure of CBZ altered blood profiles (total erythrocyte count, packed cell volume, haemoglobin) and serum biomarkers such as alkaline phosphates, cholesterol, lactate dehydrogenase and transaminase enzymes. Oxidative stress biomarkers such as superoxide dismutase (SOD) and catalase (CAT) activity were also substantially affected in all treatments. Genotoxicity study revealed the formation of micronucleus in erythrocytes of exposed fish. Integrated Biomarker Response (IBR) study showed cholesterol, serum glutamic oxaloacetic transaminase (SGOT) in serum and SOD, CAT in liver tissue are the best organ-based enzyme biomarkers. The present report concludes that an environmentally realistic concentration of CBZ can pose a serious threat to aquatic organisms.

Organochlorine pesticides: Agrochemicals with potent endocrine-disrupting properties in fish

Organochlorine pesticides (OCPs) are persistent environmental contaminants that act as endocrine disruptors and organ system toxicants. These pesticides (e.g. dichlorodiphenyltrichloroethane (DDT), dieldrin, toxaphene, among others) are ranked as some of the most concerning chemicals for human health. These pesticides (1) act as teratogens, (2) are neuroendocrine disruptors, (3) suppress the immune and reproductive systems, and (4) dysregulate lipids and metabolism. Using a computational approach, we revealed enriched endocrine-related pathways in the Comparative Toxicogenomics Database sensitive to this chemical class, and these included reproduction (gonadotropins, estradiol, androgen, steroid biosynthesis, oxytocin), thyroid hormone, and insulin. Insight from the Tox21 and ToxCast programs confirm that these agrochemicals activate estrogen receptors, androgen receptors, and retinoic acid receptors with relatively high affinity, although differences exist in their potency. We propose an adverse outcome pathway for OCPs toxicity in the fish testis as a novel contribution to further understanding of OCP-induced toxicity. Organochlorine pesticides, due to their persistence and high toxicity to aquatic and terrestrial wildlife as well as humans, remain significant agrochemicals of concern.

The histopathological, cytopathological and ultrastructural effects of carbaryl on gills of Oreochromis niloticus (Linnaeus, 1758)

Ultrastructural and histopathological reponses in the organs of living organisms are important and useful tools to determine the health condition and the effects of pollutants, such as pesticides, on the organisms. The aim of this study is to determine possible histopathological, cytopathological and ultrastructural alterations in gills of Oreochromis niloticus individuals exposed to 850 μg/L carbaryl standart at 7th, 14th and 21st days with light and electron microscopes. The fish were exposed to carbaryl for 21 days and the histopatological, ultrastructural and cytopathological alterations occuring in the gill tissues of organisms were determined by light, Scanning and Transmission Electron Microscopes (SEM and TEM). At the end of the study, it was observed that carbaryl caused both histopathological and cytopathological changes in the gills of O. niloticus. It has been determined that the most of the pathological changes in the exposed organisms are the metabolic defence reactions.

Exposure of liver cell culture from the orange-spotted grouper, Epinephelus coioides, to benzo[a]pyrene and light results in oxidative damage as measured by antioxidant enzymes

Among the various toxicants discharged into aquatic environments, benzo (a) pyrene (BaP) has been shown to effect on the antioxidant system of fish and the evaluation of its impact on biota is of considerable concern. The aim of the present study was to use the primary hepatocyte culture obtained from the orange-spotted grouper, Epinephelus coioides, to evaluate the adverse effects of benzo (a) pyrene (BaP) on cell viability and liver antioxidant system. BaP was selected for its high ability to produce reactive oxygen species (ROS) and oxidative stress. The liver was minced by a scalpel and digested in the PBS solution with 0.1% collagenase IV at room temperature for 20 min. Then, the cell suspension was transferred to a plate contained an equal amount of Leibovitz's L-15 medium with 20% fetal bovine serum (FBS), 100 IU mL^-1 of penicillin and 100 μg mL^-1 streptomycin. 5 mL of cell suspension were plated into sterile 25 cm² tissue culture flasks at the density of 1.5 × 10⁶ cell/ml L-15 and incubated at 30 °C for two weeks. The medium was renewed after 24-48 h. The number of the liver cells was adjusted to 4 × 10⁶ after two weeks. 10^-4 mol l^-1 was verified by MTT assay as the IC50 of BaP. Then, hepatocytes were exposed to three concentrations of BaP (10^-5, 2 × 10^-5, 3 × 10^-5 mol L^-1) and incubated for 24 h. Samples were collected after 6, 12 and 24 h and the amounts of SOD, CAT, GPx, LPO, LDH, AST, ALT, ALP and total protein were analyzed. The results showed that, 10^-5 mol L^-1 of BaP was not significantly toxic to cultivated hepatocytes, however, the sensitivity of cells to BaP increased in a dose-related pattern. The activity of the antioxidant enzymes (SOD, CAT and GPx) and liver enzymes (ALT, AST, ALP, LDH) significantly increased, though the amount of LPO, total antioxidant power and total protein decreased dose-dependently in BaP-exposed cells. In conclusion, according to the finding of the present study, BaP has a high potential to induce the oxidative stress in primary liver cell culture of E. coioides.

Pesticide toxicity: a mechanistic approach

Pesticides are known for their high persistence and pervasiveness in the environment, and along with products of their biotransformation, they may remain in and interact with the environment and living organisms in multiple ways, according to their nature and chemical structure, dose and targets. In this review, the classifications of pesticides based on their nature, use, physical state, pathophysiological effects, and sources are discussed. The effects of these xenobiotics on the environment, their biotransformation in terms of bioaccumulation are highlighted with special focus on the molecular mechanisms deciphered to date. Basing on targeted organisms, most pesticides are classified as herbicides, fungicides, and insecticides. Herbicides are known as growth regulators, seedling growth inhibitors, photosynthesis inhibitors, inhibitors of amino acid and lipid biosynthesis, cell membrane disrupters, and pigment biosynthesis inhibitors, whereas fungicides include inhibitors of ergosterol biosynthesis, protein biosynthesis, and mitochondrial respiration. Insecticides mainly affect nerves and muscle, growth and development, and energy production. Studying the impact of pesticides and other related chemicals is of great interest to animal and human health risk assessment processes since potentially everyone can be exposed to these compounds which may cause many diseases, including metabolic syndrome, malnutrition, atherosclerosis, inflammation, pathogen invasion, nerve injury, and susceptibility to infectious diseases. Future studies should be directed to investigate influence of long term effects of low pesticide doses and to minimize or eliminate influence of pesticides on non-target living organisms, produce more specific pesticides and using modern technologies to decrease contamination of food and other goods by pesticides.

Using a liver cell culture from Epinephelus coioides as a model to evaluate the nonylphenol-induced oxidative stress

The present study aimed to use primary liver cell culture derived from the orange-spotted grouper, Epinephelus coioides, to assess the toxic effects of nonylphenol (NP) on the hepatocyte viability and the liver antioxidant system. E. coioides was selected due to its commercial importance. NP was used in this study because of its high potential of producing oxidative stress due to increased reactive oxygen species (ROS). A liver of E. coioides was digested with PBS containing 0.1% collagenase IV. The digested cells were moved to Leibovitz L-15 culture medium with 20% fetal bovine serum (FBS), 100IUmL^-1 penicillin, 100μgmL^-1 streptomycin. Aliquots of cell suspension were seeded as a monolayer into sterile 25cm² tissue culture flasks and incubated at 30°C for 14days. The medium, containing non-attached cells, was removed after 24 to 48h and a new medium was added. The IC50 of 10^-4molL^-1 was determined for nonylphenol using MTT assay. Cells were then incubated with L-15 medium containing 10^-5, 2×10^-5, 3×10^-5molL^-1 of NP and samples were taken after 6, 12 and 24h of incubation for analysis of LPO, SOD, CAT, GPx, LDH, AST, ALT, and ALP. Based on the results, the lowest concentration of NP was not markedly cytotoxic to primary hepatocytes and the cell sensitivity to NP increased dose-dependently. The activities of SOD, CAT and GPx decreased significantly, while activities of LPO, LDH, AST, ALT and ALP, increased significantly in a dose-related pattern in NP-treated cells. In conclusion, this study revealed that NP could induce the oxidative stress in cultivated hepatocytes of E. coioides during a short-term exposure. NP toxicity is mainly due to the induction of the reactive oxygen species (ROS), which lead to cell membrane disruption, damage of cellular metabolism, and interference with cellular macromolecules.

Immune and physiological responses of pufferfish (Takifugu obscurus) under cold stress

Low temperature is an important environmental factor in aquaculture farming that affects the survival and growth of organisms. In the present study, we investigated the effects of low temperature on biochemical parameters, oxidative stress and apoptosis in pufferfish. In the stress group, water temperature decreased from 25 °C to 13 °C at a rate of 1 °C/1 h. Fish blood and liver were collected to assay biochemical parameters, oxidative stress and expression of genes at 25 °C, 21 °C, 17 °C, 13 °C and 13 °C for 24 h. The results showed that low temperature could decrease total blood cell count, inhibit cell viability, and subsequently lead to DNA damage. Biochemical parameters such as plasma protein and ALP significantly declined in fish under low temperature, while a significant increase in AST, ALT, LDH and glucose was observed. The gene expression of antioxidant enzymes (SOD and CAT), HSP90 and C3 were induced by low temperature stress. Furthermore, the gene expression of apoptotic related genes including P53, caspase-9 and caspase-3 were up-regulated, suggesting that caspase-dependent pathway could play important roles in low temperature-induced apoptosis in fish. This study may provide baseline information about how cold stress affects the physiological responses and apoptosis in fish.

Differential expression and characterization of cypermethrin-degrading potential proteins in Bacillus thuringiensis strain, SG4

A cypermethrin-degrading bacterium (SG4) was isolated from the pesticide-contaminated soil in the agricultural field of the crop research centre of the University, and characterized as Bacillus thuringiensis strain, SG4. The bacterium degraded 78.9 % of cypermethrin (50 ppm) in 15 days when grown in a minimal medium. To understand the functional proteins of cypermethrin degradation in Bacillus thuringiensis strain SG4, a comparative proteomic analysis was performed in the presence/absence of cypermethrin after 5 days of incubation in minimal medium. More than 450 spots corresponding to different proteins were recorded by 2D electrophoresis. We report expression of 223 and 250 unique proteins under normal and induced conditions (cypermethrin stress), respectively. Identified proteins were categorized into different functional groups on the basis of their biological functions, viz., catabolic enzymes, translational and stress proteins, etc. Characterization of cypermethrin-specific proteins in a bacterial strain will help in biodegradation practices in situ.

Differential protein expression in the susceptible and resistant Myzus persicae (Sulzer) to imidacloprid

Myzus persicae, a serious economic agricultural pest, has developed resistance to imidacloprid (IMI), which was widely used to control this aphid worldwide. To gain a better understanding of the mechanisms of IMI resistance in M. persicae, we carried out a comparative proteomic analysis. Total proteins of the IMI-susceptible and resistant strains were extracted and separated by two-dimensional gel electrophoresis. More than 1300 protein spots were reproducibly detected, including 14 that were more abundant and 14 less abundant. Mass spectrometry analysis and database searching helped us to identify 25 differentially abundant proteins. The identified proteins were categorized into several functional groups including signal transduction, RNA processing, protein processing, transport processing, stress response, metabolisms, and cytoskeleton structure, etc. This study is the first analysis of differentially expressed proteins in IMI-susceptible and resistant M. Persicae, and gives new insights into the mechanisms of IMI resistance in M. persicae.

Cytotoxic effect of fenitrothion and lambda-cyhalothrin mixture on lipid peroxidation and antioxidant defense system in rat kidney

A mixture of pyrethroids plus organophosphates was assessed for their potential effects on lipid peroxidation, the antioxidant defense system and lactate dehydrogenase (LDH) in rat kidney in vitro. Various insecticide concentrations were incubated with kidney homogenate at 37°C for different incubation times. Treatment with fenitothion (FNT) plus lambda-cyhalothrin (LC) caused a significant induction (P < 0.05) in thiobarbituric acid reactive substances (TBARS), which might be associated to decreased levels of reduced glutathione (GSH), superoxide dismutase (SOD), catalase (CAT), glutathione S-transferase (GST) activities and protein content in rat kidney. However, a significant induction of lactate dehydrogenase (LDH) activity was observed. The effect was concentration and time dependent. It can be concluded that depletion of GSH might indicate that reactive oxygen species (ROS) could be involved in the toxic effects of FNT plus LC which lead to marked perturbations in antioxidant defense system.

Use of hematological and plasma biochemical parameters to assess the chronic effects of a fungicide propiconazole on a freshwater teleost

Blood is an indicator of physiological condition of an animal. Therefore, the chronic effects of propiconazole, a triazole fungicide present in aquatic environment, on hematology of rainbow trout were investigated in this study. Fish were exposed at various concentrations of PCZ (0.2, 50 and 500 μg L(-1)) for 7, 20 and 30 d. Multiple biomarkers were measured, including hematological indices (hemoglobin concentration, red blood cells count, hematocrit, leukocyte count, mean erythrocyte hemoglobin, mean erythrocyte volume and mean color concentration) and plasma biochemical parameters (ammonia, glucose, total proteins, creatine kinase, lactate dehydrogenase, alanine aminotransferase and aspartate aminotransferase). Through principal component analysis and integrated biomarker response assessment, influence extent induced by PCZ-stress of each test group was distinguished. Additional, all parameters measured in this study displayed different dependent patterns to PCZ concentrations and exposure time by two-way ANOVA. The results of this study indicate that chronic exposure of PCZ has altered multiple physiological indices in fish hematology and CK activity may be an early biomarker of PCZ toxicity; however, before these parameters are used as special biomarkers for monitoring residual PCZ in aquatic environment, more detailed experiments in laboratory need to be performed in the future.

Acute toxicity of carbamazepine to juvenile rainbow trout (Oncorhynchus mykiss): effects on antioxidant responses, hematological parameters and hepatic EROD

Awareness of residual pharmaceutically active compounds (PhACs) in the aquatic environment is growing as investigations into these pollutants are increasing and analytical detection techniques are improving. However, the toxicological effects of PhACs have not been adequately researched. In this study, the toxic effects of carbamazepine (CBZ), an anticonvulsant drug commonly present in surface and groundwater, was studied in juvenile rainbow trout, Oncorhynchus mykiss, by acute semi-static bioassay. Blood parameters, liver xenobiotic-metabolizing response and tissue antioxidant status were evaluated. Compared to the control group, fish exposed to CBZ (96 h LC50) showed significantly higher Er, Hb, MCHC, monocytes, neutrophil granulocytes and plasma enzymes activity, and significantly lower MCV and lymphocytes. CF and HSI were not significantly different among groups such as hepatic EROD. SOD, CAT, GPx and GR activity was significantly higher in liver of experimental groups, but decreased significantly in brain and gill. In general, antioxidant enzyme activity in intestine and muscle was less evident than in liver. Oxidative stress indices (levels of LPO and CP) were significantly higher in gill and brain, despite a trend to increased values were manifested in the remaining tissues. In short, CBZ-induced stress responses in different tissues were reflected in the oxidant stress indices and hematological parameters. However, before those parameters are used as special biomarkers for monitoring residual pharmaceuticals in aquatic environment, more detailed experiments in laboratory need to be performed in the future.

Chronic toxicity of verapamil on juvenile rainbow trout (Oncorhynchus mykiss): effects on morphological indices, hematological parameters and antioxidant responses

In this study, the toxic effects of verapamil (VRP) were studied on juvenile rainbow trout, Oncorhynchus mykiss, by chronic semi-static bioassay. Fish were exposed to sublethal concentrations of VRP (0.5, 27 and 270 μg/L) for 0, 21 and 42 d. Multiple biomarkers were measured, including morphological indices, hematological parameters and antioxidant responses of different tissues (brain, gill, liver, muscle and intestine). Based on the results, there was no significant change in all parameters measured in fish exposed to VRP at environmental related concentration, but VRP-induced stress in fish exposed to higher concentrations reflected the significant changes of physiological and biochemical responses. Through principal component analysis and integrated biomarker response assessment, effects induced by VRP-stress in each test group were distinguished. Additionally, all parameters measured in this study displayed various dependent patterns to VRP concentrations and exposure time using two-way ANOVA statistic analysis. In short, the multiple responses in fish indicated that VRP induced physiological stress and could be used as potential biomarkers for monitoring residual VRP in aquatic environment; but molecular and genetic mechanisms of these physiological responses in fish are not clear and need to be further studied.

Oxidative stress induced by lambda-cyhalothrin (LTC) in rat erythrocytes and brain: Attenuation by vitamin C

The objective of this study was to investigate the propensity of lambda-cyhalothrin (LTC) to induce oxidative stress in blood and brain of male Wistar rats and its possible attenuation by vitamin C. Rats were randomly divided into four groups: group I served as control rats. group II was treated daily with 200mgvit C/(kgbw) administered by intraperitoneal way. Rats of group III have received orally 668ppm LTC. Animals of group IV were treated with LTC and vitamin C. A decrease of some hematologic parameters (RBC, Hb, Ht: p<0.01) and a significant increase of MDA levels (p<0.05) in erythrocytes and brain were observed in LTC group compared to controls. Antioxidant enzyme activities in both tissues were modified in LTC group compared to controls. Administration of vitamin C ameliorated these parameters. Our results indicated the potential effects of LTC to induce oxidative damage in tissues and the ability of vitamin C to attenuate LTC-induced oxidative damage.

Sensitivity of Atlantic salmon (Salmo salar) to dietary endosulfan as assessed by haematology, blood biochemistry, and growth parameters

The presence of the organochlorine pesticide endosulfan in the water column confers a significant direct risk to the biota therein, yet relatively little is known regarding the toxic impact of dietborne endosulfan to aquatic organisms. Pre-smolt Atlantic salmon (Salmo salar) were fed at levels of technical endosulfan equal to the European Union regulatory limit (5 microg kg(-1)) and at levels 10 and 100 times greater, for a total of 49 days with haematology (e.g. erythrocyte count, haemoglobin, haematocrit, white blood cell composition), blood biochemistry (e.g. serum aminotransferase, plasma ions) and growth parameters (e.g. condition factor) recorded at days 0, 14, 35, and 49. Toxicological assessment of the individual alpha and beta-isomers that comprise technical endosulfan was also attempted. No mortality was observed in any group during the experiment. In the groups exposed to the control, 5, and 50 microg kg(-1) technical endosulfan feeds no significant alterations in any measured parameters were determined at any time point. No differences were observed between the technical mixture and the individual alpha and beta-isomer treatment groups. Condition factor was significantly reduced in fish exposed to 500 microg kg(-1) at day 49, while haematocrit, haemoglobin and mean corpuscular haemoglobin were significantly elevated after 35 days of exposure to the same dietary level, but returned to control levels by day 49. The present study shows that with regards to acute toxicity, Atlantic salmon are able to tolerate dietary technical endosulfan levels up to 500 microg kg(-1).

Changes in oxygen consumption and respiratory enzymes as stress indicators in an estuarine edible crab Scylla serrata exposed to naphthalene

The sublethal effect of naphthalene was studied on the physiology of a mud crab Scylla serrata. The 96 h acute toxicity of naphthalene was determined and found to be 28 mg 1(-1) (LC100), 18 mg 1(-1) (LC50), 10 mg 1(-1) (LC0) respectively. The 30 days sublethal effect (LC0) 9 mg 1(-1), 8 mg 1(-1), 10 mg 1(-1), of naphthalene was investigated in the crab S. serrata with reference to oxygen consumption and changes in the activity of respiratory enzymes. The results indicated that naphthalene caused disturbance in the normal physiology of the crab. The bioaccumulation of naphthalene was also investigated in gills, hepatopancreas, haemolymph and ovary. The consumption of oxygen increased in the naphthalene medium when compared with that of the crabs exposed to naphthalene free medium. A decreased trend in the activity of respiratory enzymes such as lactate dehydrogenase (LDH), isocitrate dehydrogenase (ICDH), succinate dehydrogenase (SDH), malate dehydrogenase (MDH), alpha-ketoglutarate dehydrogenase (alpha-KDH) and glutathione (GSH) were recorded in the hepatopancreas, ovary and gills of S. serrata for all the tested concentrations of naphthalene and the results were analyzed for their significance.

Proteome modifications of blue mussel (Mytilus edulis L.) gills as an effect of water pollution

The discharge of chemicals such as oil associated or not with derived products constitutes a real threat for the environment. We report here the differential expression of the blue mussel (Mytilus edulis) gill proteins corresponding to two contaminated environmental conditions: crude oil and offshore produced water. In order to evaluate and understand contaminants, effects and adaptive response of these organisms, we identified proteins using MS. The latter can be grouped into three main classes: proteins involved in the cellular structure, in metabolism, and in defence proteins.

Fluctuations of biochemical constituents and marker enzymes as a consequence of naphthalene toxicity in the edible estuarine crab Scylla serrata

The sublethal effects of naphthalene on protein, deoxyribonucleic acid (DNA), ribonucleic acid (RNA), carbohydrates, lipids, and certain marker enzymes such as phosphatases, transaminases, and lactate dehydrogenase were studied in hepatopancreas, hemolymph, and ovary in the edible crab Scylla serrata. The results revealed that there was overall decrease in total protein, total DNA, total RNA, free sugar, glycogen, protein-bound sugars, neutral lipid, glycolipid, and phospholipid in the test samples compared to control. Similarly all the marker enzymes (acid phosphatase, alkaline phosphatase, aspartate transaminase, alanine transaminase, and lactate dehydrogenase) were decreased in hepatopancreas and ovary. On the other hand, in hemolymph, the activities of marker enzymes were increased. The results were tested statistically and interpreted accordingly.

Endocrine response of the freshwater teleost, Sarotherodon mossambicus (Peters) to dimecron exposure

The endocrine response in a freshwater teleost, Sarotherodon mossambicus (Peters) under dimecron (an organophosphate pesticide) toxicity was investigated by estimating the serum levels of T3 (triiodothyronine), T4 (thyroxine), cortisol, prolactin and insulin in control and sub-lethal (0.001 ml l(-1)) dimecron-exposed fish for 1, 6, 12, 24h and 5 days. In control S. mossambicus, the serum levels of T3 ranged from 0.80+/-0.01 to 0.82+/-0.01 ng ml(-1); T4 from 2.20+/-0.01 to 2.25+/-0.01 microg dl(-1); cortisol from 8.30+/-0.03 to 8.34+/-0.01 microg dl(-1); prolactin from 1.50+/-0.01 to 1.54+/-0.01 microg ml(-1); insulin from 9.70+/-0.01 to 9.76+/-0.01 microU ml(-1) up to a maximum period of 5 days maintained in pollutant-free tap water. Exposure of fish to sub-lethal concentration of dimecron caused varying changes in the levels of serum hormones studied. Based on the results obtained, it was concluded that (i) the fish adaptively maintains a probable low metabolic rate, as indicated by the reduced levels of thyroid hormone (T3) as well as the glucocorticoid hormone (cortisol), which could be considered advantageous for the fish to indirectly reduce the toxic impact of the pesticide, (ii) the elevated levels of prolactin in the fish under pesticide stress is indicative of a possible hydromineral regulatory effect of the hormone (probably by influencing specific organs such as gills and kidney) under pesticide toxicity, (iii) the increased insulin level in the fish under pesticide stress is indicative of its role in favouring an adaptive tissue glycogenesis besides a possible increased lipogenesis to sequester the pesticide residue thereby reducing the toxic effect of the pesticide and (iv) the prolonged exposure of the fish (for 5 days) to sub-lethal dimecron appeared to exhibit a uniform recovery response in the different hormonal levels of the fish.