Metallothionein as Potential Biomarker of Cadmium Exposure in Persian Sturgeon (<Emphasis Type="Italic">Acipenser persicus</Emphasis>)

Metallothionein (MT) concentration in gills, liver, and kidney tissues of Persian sturgeon (Acipenser persicus) were determined following exposure to sublethal levels of waterborne cadmium (Cd) (50, 400, and 1,000 μg l⁻¹) after 1, 2, 4, and 14 days. The increases of MT from background levels were 4.6-, 3-, and 2.8-fold for kidney, liver, and gills, respectively. The results showed that MT level change in the kidney is time and concentration dependent. Also, cortisol measurement revealed elevation at the day 1 of exposure and followed by MT increase in the liver. Cd concentrations in the cytosol of experimental tissues were measured, and the results indicated that Cd levels in the cytosol of liver, kidney, and gills increased 240.71-, 32.05-, and 40.16-fold, respectively, 14 days after exposure to 1,000 μg l⁻¹ Cd. The accumulation of Cd in cytosol of tissues is in the order of liver > gills > kidney. Pearson correlation coefficients showed that the MT content in kidney is correlated with Cd concentration, the value of which is more than in liver and gills. Thus, kidney can be considered as a tissue indicator in A. persicus for waterborne Cd contamination.     

Temporal changes in liver carbohydrate metabolism associated with seawater transfer in Oreochromis mossambicus

The metabolic aspects of ionic and osmotic regulation in fish are not well understood. The objective of this study was to examine changes in carbohydrate metabolism during seawater (SW) acclimation in the euryhaline tilapia (Oreochromis mossambicus). Hepatic activities of three key enzymes of the intermediary metabolism, phosphofructokinase, glycogen phosphorylase and glucose 6-phosphate dehydrogenase, together with glycogen content and plasma glucose concentration were measured at 0, 0.5, 1, 2, 3, 6, 12, 24, 48 and 96 h after the direct transfer of tilapia from fresh water (FW) to 70% SW. Plasma growth hormone, prolactin₁₇₇ and prolactin₁₈₈, Na⁺ and Cl⁻ concentrations were also measured. Plasma Na⁺ and Cl⁻ levels were highest at 12 h, but returned to FW levels at 24 h after transfer, suggesting the tilapia were able to osmoregulate within 24 h after transfer. Plasma glucose levels were significantly higher in 70% SW than in FW during the course of acclimation, especially in the early stages. Hepatic enzyme activities and glycogen content did not change significantly during the acclimation period. Our results suggest the possibility that glucose is an important energy source for osmoregulation during the acclimation to hyperosmotic environments in O. mossambicus.     

Correlation between metallothionein and energy metabolism in sea bass,Dicentrarchus labrax,exposed to cadmium

Specimens of sea bass (Dicentrarchus labrax) were exposed to two different cadmium concentrations (0.5 and 5 μg Cd²⁺/ml seawater) for a period of 7 days. Cadmium accumulated in the tissues of D. labrax in the following order: kidney > liver > gills at both concentrations. Accumulation patterns in fish exposed to 0.5 μg Cd²⁺/ml seawater were different with respect to 5.0 μg Cd²⁺/ml seawater. At both Cd concentrations a similar stress situation occurred during the first 4 hr as noted by the depletion of glycogen stores and the increase in free glucose in the muscle; metallothionein was induced in the liver, but failed to bind all the cytosolic Cd, which was in part bound to high-molecular-weight ligands. Fish recovered from this initial stress situation within 24 hr as indicated by the increase in glycogen and the decrease of glucose. Long-term effects were clearly dependent upon metal concentration: at lower Cd exposure, metallothionein induction increased linearly with time and counteracted the toxic effect of the metal; on the other hand, when fish were exposed to 5.0 μg Cd²⁺/ml seawater a clear stress occurred at the end of the exposure, as indicated by the notable decrease of glycogen stores, the increase of free glucose, the decrease of AEC in the muscle and the increase of Cd bound to high-molecular-weight ligands in the liver.     

Diet with Diphenyl Diselenide Mitigates Quinclorac Toxicity in Silver Catfish (Rhamdia quelen)

In this study, the protective effects of diphenyl diselenide [(PhSe)₂] on quinclorac- induced toxicity were investigated in silver catfish (Rhamdia quelen). The fish were fed for 60 days with a diet in the absence or in the presence of 3.0 mg/Kg (PhSe)₂. Animals were further exposed to 1 mg/L quinclorac for 8 days. At the end of experimental period, fish were euthanized and biopsies from liver and gills, as well as blood samples, were collected. The cortisol and metabolic parameters were determined in plasma, and those enzyme activities related to osmoregulation were assayed in the gills. In liver, some important enzyme activities of the intermediary metabolism and oxidative stress-related parameters, such as thiobarbituric acid-reactive substance (TBARS), protein carbonyl, catalase (CAT), superoxide dismutase (SOD), glutathione S-transferase (GST), nonprotein thiols (NPSH) and ascorbic acid contents were also evaluated. Compared to the control group, quinclorac exposure significantly decreased hepatosomatic index and increased cortisol and lactate values in plasma. Moreover, the activities of fructose biphosphatase (FBPase), glucose-6-phosphate dehydrogenase (G6Pase), glycogen phosphorilase (GPase) and aspartate aminotransferase (AST) were significantly increased in liver. Quinclorac also induced lipid peroxidation while the activity of SOD, NPSH and ascorbic acid levels decreased in the liver. However, dietary (PhSe)₂ reduced the herbicide-induced effects on the studied parameters. In conclusion, (PhSe)₂ has beneficial properties based on its ability to attenuate toxicity induced by quinclorac by regulating energy metabolism and oxidative stress-related parameters.     

In vivo and in vitro effects of cadmium on selected enzymes in different organs of the fish Barbus conchonius ham. (Rosy Barb)

1. Enzyme modulation by cadmium in selected organs of the fish, Barbus conchonius (rosy barb), was investigated in vivo (48 hr exposure to 12.6 mg/1 cadmium chloride) and in vitro (10⁻⁶M cadmium chloride).2. The acetylcholinesterase (AchE) activity was depressed in the gills but stimulated in the skeletal muscles and brain in vivo. The hepatic, branchial, and renal acid phosphatase (AcP) activity decreased marginally in vivo but it was significantly increased in the gut and ovary. In vitro, except for the liver, the AcP activity was depressed in the selected organs. Collaterally, gut alkaline phosphatase (A1P) was significantly inhibited but a pronounced stimulation was noted in the kidneys and ovary in vivo. In vitro, the AIP activity was conspicuously elevated in the kidneys and gut, and moderately in the gills.3. Cadmium inhibited the glutamate-oxaloacetate and glutamate-pyruvate transaminases (GOT and OPT) in the liver, gills and kidneys in vivo. In vitro, the GOT and GPT activities were decreased in the liver, gills and kidneys. The lactic dehydrogenase (LDH) was significantly stimulated by Cd in the heart in vivo but in vitro the metal inhibited the enzyme in the gills.4. Enzymes in the liver, followed by those in the kidneys and gills seem to be most seriously affected by Cd poisoning in this fish.     

Effects of spironolactone and RU486 on gene expression and cell proliferation after freshwater transfer in the euryhaline killifish

We have explored the possible mechanisms by which mineralocorticoid (MR) and glucocorticoid (GR) receptors regulate the response to freshwater transfer in the gills of the euryhaline killifish Fundulus heteroclitus. Killifish were implanted with RU486 (GR antagonist) or spironolactone (MR antagonist) at doses of 0.1–1.0 mg g⁻¹, and subsequently transferred from 10‰ brackish water to freshwater. Compared to brackish water sham fish, mRNA expression of CFTR and NKCC1 decreased in the gills of sham fish transferred to freshwater, whereas Na⁺,K⁺–ATPase α_1a mRNA expression and α protein abundance, as well as cell proliferation (detected using BrdU) increased. Spironolactone inhibited the normal increase in cell proliferation and Na⁺,K⁺-ATPase expression after freshwater transfer. RU486 increased plasma cortisol levels and may have slightly inhibited Na⁺,K⁺–ATPase activity, but did not change α _1a expression. RU486 had no effect on cell proliferation in the non-lamellar region of the gills, but increased proliferation in the lamellar region. Neither antagonist inhibited the suppression of CFTR or NKCC1 expression after freshwater transfer. Glucocorticoid receptor expression was reduced in all sham and antagonist treatments compared to untreated controls, but no other consistent differences were observed. The effects of spironolactone suggest that MR is important for regulating ion transport in killifish gills after freshwater transfer.     

Influence of highly unsaturated fatty acids on the responses of white shrimp (Litopenaeus vannamei) postlarvae to low salinity

Salinity stress tests are commonly applied in shrimp hatcheries to estimate the quality of postlarvae (PL) to be used during growout. Higher larval survival during culture and to a salinity stress test in both fish and crustaceans have been reported when specimens were offered a diet containing high levels of highly unsaturated fatty acids (HUFA). However, it is not clear if increased survival is a result of better overall physiological condition resulting from the diet or a specific effect of HUFA on osmoregulatory mechanisms. This study analyzed if HUFA-rich diets could modify the fatty acid composition of membranes in gills, and if this change in composition could affect the activity of the Na⁺/K⁺ ATPase pump and carbonic anhydrase in relation to changes in salinity. One-day-old postlarvae (PL1) pooled from different spawns were fed for 20 days with Artemia sp. nauplii enriched with three levels of HUFA: low, medium and high. At PL20, survivals during culture and to salinity stress test (tap water for 30 min) were evaluated. Also at this stage, Na⁺/K⁺-ATPase and carbonic anhydrase activity, morphometric variables, and fatty acid composition in the hepatopancreas and gills were measured after they were submitted to a salinity challenge in dilute seawater (10 ppt) for 3 h. No significant differences were observed in survival rates during culture, but survival to a salinity stress test was higher and gill area was larger in PL20 fed the Artemia sp. nauplii enriched with medium HUFA levels, probably as a result of an increased 22:6n-3 content and higher 22:6n-3/20:5n-3 ratio in this diet and in the tissues of the organisms fed this diet. Na⁺/K⁺-ATPase specific activity was significantly higher in posterior gills, while the specific activity of the carbonic anhydrase was higher in anterior gills. Enzymatic activities increased significantly in PL20 submitted to a salinity challenge, and HUFA levels in the diet affected both. The proportion of fatty acids in hepatopancreas and gills were significantly affected not only by diet, but also by exposure to dilute media. This effect is discussed in relation to an increase in gill surface and changes in fatty acid composition in the phospholipids present in gill membranes, which can modify the permeability and the activity of the Na⁺/K⁺-ATPase pump. The beneficial effect of HUFA supplementation in the diet on survival to salinity stress test is partially related to modification of fatty acid composition of gills and to a larger gill area, which in turn enhances osmoregulatory mechanisms, namely Na⁺/K⁺-ATPase and carbonic anhydrase activities.     

Effects of High-Potassium-Induced Depolarization on Amino Acid Chemistry of the Dorsal Cochlear Nucleus in Rat Brain Slices

High K⁺ was used to depolarize glia and neurons in order to study the effects on amino acid release from and concentrations within the dorsal cochlear nucleus (DCN) of brain slices. The release of glutamate, -aminobutyrate (GABA) and glycine increased significantly during exposure to 50 mM K⁺, while glutamine and serine release decreased significantly during and/or after exposure, respectively. After 10 min of exposure to 50 mM K⁺, glutamine concentrations increased in all three layers of DCN slices, to more than 5 times the values in unexposed slices. In the presence of a glutamate uptake blocker, L-trans-pyrrolidine-2,4-dicarboxylic acid (PDC), glutamine concentrations in all layers did not increase as much during 50 mM K⁺. Similar but smaller changes occurred for serine. Mean ATP concentrations were lower in 50 mM K⁺-exposed slices compared to control. The results suggest that depolarization, such as during increased neural activity, can greatly affect amino acid metabolism in the cochlear nucleus.     

Food deprivation alters osmoregulatory and metabolic responses to salinity acclimation in gilthead sea bream Sparus auratus

The influence of acclimation to different environmental salinities (low salinity water, LSW; seawater, SW; and hyper saline water, HSW) and feeding conditions (fed and food deprived) for 14 days was assessed on osmoregulation and energy metabolism of several tissues of gilthead sea bream Sparus auratus. Fish were randomly assigned to one of six treatments: fed fish in LSW, SW, and HSW, and food-deprived fish in LSW, SW, and HSW. After 14 days, plasma, liver, gills, kidney and brain were taken for the assessment of plasma osmolality, plasma cortisol, metabolites and the activity of several enzymes involved in energy metabolism. Food deprivation abolished or attenuated the increase in gill Na⁺,K⁺-ATPase activity observed in LSW- and HSW-acclimated fish, respectively. In addition, a linear relationship between renal Na⁺,K⁺-ATPase activity and environmental salinity was observed after food deprivation, but values decreased with respect to fed fish. Food-deprived fish acclimated to extreme salinities increased production of glucose through hepatic gluconeogenesis, and the glucose produced was apparently exported to other tissues and served to sustain plasma glucose levels. Salinity acclimation to extreme salinities enhanced activity of osmoregulatory organs, which is probably sustained by higher glucose use in fed fish but by increased use of other fuels, such as lactate and amino acids in food-deprived fish.     

Main features of the oxidative metabolism in gills and liver of Odontesthes nigricans Richardson (Pisces, Atherinopsidae)

The aim of this work was to study comparatively the oxidative metabolism in gills and liver of a silverside, Odontesthes nigricans, in their natural environment, the Beagle Channel. Oxidative damage to lipids was evaluated by assessing TBARS and lipid radical content, in gills and liver. Gills showed a significantly higher degree of damage than liver. The content of α-tocopherol, β-carotene and catalase activity showed significantly higher values in the liver than in the gills. The ascorbyl radical (A^•) content showed no significant differences between gills and liver. The ascorbate (AH⁻) content was 12 ± 2 and 159 ± 28 nmol/mg FW in gills and liver, respectively. Oxidative metabolism at the hydrophilic level was assessed as the ratio A^•/AH⁻. The ratio A^•/AH⁻ was significantly different between organs, (6 ± 2)10^− 5 and (5 ± 2)10^− 6, for the gills and the liver, respectively. Both, lipid radical content/α-tocopherol content and lipid radical content/β-carotene content ratios were significantly higher in gills as compared to the values recorded for the liver, suggesting an increased situation of oxidative stress condition in the lipid phase of the gills. Taken as a whole, the O. nigricans liver exhibited a better control of oxidative damage than the gills, allowing minimization of intracellular damage when exposed to environmental stressing conditions.     

Growth hormone transgenesis affects osmoregulation and energy metabolism in zebrafish (Danio rerio)

Growth hormone (GH) transgenic fish are at a critical step for possible approval for commercialization. Since this hormone is related to salinity tolerance in fish, our main goal was to verify whether the osmoregulatory capacity of the stenohaline zebrafish (Danio rerio) would be modified by GH-transgenesis. For this, we transferred GH-transgenic zebrafish (T) from freshwater to 11 ppt salinity and analyzed survival as well as relative changes in gene expression. Results show an increased mortality in T versus non-transgenic (NT) fish, suggesting an impaired mechanism of osmotic acclimation in T. The salinity effect on expression of genes related to osmoregulation, the somatotropic axis and energy metabolism was evaluated in gills and liver of T and NT. Genes coding for Na⁺, K⁺-ATPase, H⁺-ATPase, plasma carbonic anhydrase and cytosolic carbonic anhydrase were up-regulated in gills of transgenics in freshwater. The growth hormone receptor gene was down-regulated in gills and liver of both NT and T exposed to 11 ppt salinity, while insulin-like growth factor-1 was down-regulated in liver of NT and in gills of T exposed to 11 ppt salinity. In transgenics, all osmoregulation-related genes and the citrate synthase gene were down-regulated in gills of fish exposed to 11 ppt salinity, while lactate dehydrogenase expression was up-regulated in liver. Na⁺, K⁺-ATPase activity was higher in gills of T exposed to 11 ppt salinity as well as the whole body content of Na⁺. Increased ATP content was observed in gills of both NT and T exposed to 11 ppt salinity, being statistically higher in T than NT. Taking altogether, these findings support the hypothesis that GH-transgenesis increases Na⁺ import capacity and energetic demand, promoting an unfavorable osmotic and energetic physiological status and making this transgenic fish intolerant of hyperosmotic environments.     

Effect of cadmium on antioxidant enzyme activities and lipid peroxidation in the gills of the clam Ruditapes decussatus

Metals are known to influence the oxidative status of marine organisms, and antioxidant enzymes have been often proposed as biomarkers of effect. The clam Ruditapes decussatus is a well-known metal bioindicator. In this species cadmium (Cd) induces metallothionein (MT) synthesis only after 7 days of exposure. Before MT synthesis is induced, the other mechanisms capable of handling the excess of Cd are unknown. In order to identify some of these mechanisms, variations in antioxidant systems (superoxide dismutase, catalase, selenium-dependent glutathione peroxidase and non-selenium-dependent glutathione peroxidase), malondialdehyde (MDA) and MT were studied in the gills of R. decussatus exposed to different Cd concentrations (4, 40 and 100 gl^-1) for 28 days. These parameters, together with total proteins and Cd concentrations, were measured in the gills of the clams over different periods of exposure. Results indicate that Cd accumulation increased linearly in the gills of R. decussatus with the increase in Cd concentration. This increase induces an imbalance in the oxygen metabolism during the first days of Cd exposure. An increase in cytosolic superoxide dismutase (SOD) activity and a decrease in mitochondrial SOD activity was observed at the same time as or after a decrease in cytosolic and mitochondrial catalase activity and of selenium-dependent and non-selenium-dependent glutathione peroxidase activity. After 14 days of exposure, Cd no longer affect these enzymes but there was elevation of other cellular activities, such as MDA and MT production. MT bound excess Cd present in the cell. These variations in these parameters suggest their potential use as biomarkers of effects such as oxidative stress resulting from Cd contamination in molluscs.     

The response of sea bream following abrupt hyposmotic exposure

The response of a marine teleost, silver sea bream Sparus sarba, to abrupt hyposmotic exposure was investigated over a 120-h period following direct exposure from sea water (SW, 33‰) to a hyposmotic environment of 6‰. Aspects of serum chemistry, stored metabolites and gill morphology were used to gain further insight into the biochemical, physiological and morphological alterations that take place following low salinity exposure of a marine fish. Rapid (<1 h) reductions in serum [Cl^?] occurred while serum [Na⁺] exhibited only transient perturbations during initial exposure. Serum total [Ca] declined 24 h after exposure and returned to pre-exposure levels by 120 h. Despite a tendency for muscle moisture to increase during the early stages of low salinity exposure to significant change could be detected. The response of the branchial chloride cell (CC) was rapid, with apical and fractional exposure area increasing after 6 h. The number of CCs exposed at the branchial surface reduced after 6 h but subsequently increased to elevated levels. Serum cortisol levels had increased three fold 1 h after hyposmotic exposure and stabilised at pre-exposure levels within 12–24 h. Serum triiodothyronine (T 3 ) levels exhibited a biphasic response, significantly elevating and decreasing after 3 and 6 h respectively. Significant post-hyposmotic exposure elevations in serum glucose and protein occurred after 1 h, peaking at 3 h and returning to lower levels after 6 h. Total free ninhydrin reactive substances were significantly elevated 3 h post-hyposmotic exposure, a phenomenon attributable to elevated levels of ammonia, alanine, arginine, glycine, isoleucine, lysine, methionine, phenylalanine, serine, taurine, threonine and valine. Of these substances, glycine, lysine, serine and taurine remained elevated for up to 12 h or longer. Serum urea levels elevated 1 h after exposure to 6%‰ and returned to SW levels 3 h post-exposure. The relevance of these results is discussed within the context of current knowledge on the effects of hyposomotic adaptation on marine fish.     

Effect of battery-manufacturing effluent on endogenous antioxidant in freshwater fish

Abstract

This study monitors and assesses the effect of battery-manufacturing effluent containing metals Pb, Zn and Cd on endogenous antioxidants. Malonaldehyde (MDA), reduced glutathione sulfyhydryl (GSH) and catalase (CAT) which are known biomarkers of effluent were exposed to 0%, 25%, 50%, 75% and 90% amendments for 74h on the gills, liver and kidneys of C. punctata. There was more metal Zn accumulation in the gills and GSH contents increased significantly in the gills (P<0.01), liver accumulation of Pb was found to be more (P<0.05), whereas lowest accumulation of Pb was found in kidneys and the highest accumulation of Cd (P<0.05). Over all amendments of the effluents, MDA contents were increased in the gills, liver and kidneys (P<0.01). GSH levels were decreased among the liver and kidneys compared to the gills (P<0.01) at 90% amendment. Effluent exposure caused a significant decrease in the activities of CAT in the gills, liver and kidneys (P<0.01, 0.05 and 0.05) of fish. Increased MDA activity was indicative of the formation of free radicals in the fish with exposure to amendments of battery manufacturing effluent, while increased levels of GSH pointed to the occurrence of a scavenging mechanism of free radicals.     

Monitoring of Na<Superscript>+</Superscript>/K<Superscript>+</Superscript>-ATPase mRNA expression in the cinnamon clownfish, <Emphasis Type="Italic">Amphiprion melanopus</Emphasis>, exposed to an osmotic stress environment: profiles on the effects of exogenous hormone

We examined changes in the expression of Na⁺/K⁺-ATPase mRNA in the gills of the cinnamon clownfish using quantitative real-time PCR in an osmotically changing environment [seawater (35 psu; practical salinity unit, 1 psu ≈ 1‰) → brackish water (17.5 psu) and brackish water with prolactin]. The expression of Na⁺/K⁺-ATPase mRNA in gills was increased after the transfer to brackish water, and the expression was repressed by prolactin treatment. Also, activities of gill Na⁺/K⁺-ATPase and plasma cortisol levels increased after the transfer to brackish water and were repressed in brackish water with prolactin treatment. Na⁺/K⁺-ATPase-immunoreactive cells were almost consistently observed in the gill filaments, but absent from the lamella epithelia. The plasma osmolality level decreased in brackish water, but the level of this parameter increased in brackish water with prolactin treatment during salinity change. These results suggest that the Na⁺/K⁺-ATPase gene plays an important role in osmoregulation in gills, and prolactin improves the hyperosmoregulatory ability of cinnamon clownfish in a brackish water (hypoosmotic) environment.     

Effect of fasting on glycogen metabolism and activities of glycolytic and gluconeogenic enzymes in the mudskipper Boleophthalmus boddaerti

During starvation, muscle glycogen in Boleophthalmus boddaerti was utilized preferentially over liver glycogen. In the first 10 days of fasting, the ratio of the active‘a’form of glycogen phosphorylase to total phosphorylase present in the liver was small. During this period, the active‘I’form of glycogen synthetase increased in the same tissue. In the muscle, the phosphorylase‘a’activity declined during the first 7 days and increased thereafter while the total glycogen synthetase activity showed a drastic decline during the first 13 days of fasting. The glycogen level in the liver and muscle of mudskippers starved for 21 days increased after refeeding. After 6 and 12 h refeeding, liver glycogen level was 8·5 ± 2·3 and 6·9 ± 4·5 mg·g wet wt ¹, respectively, as compared to 5·8 ± l·6mg·g wet wt ¹ in unfed fish. Muscle glycogen level after 6 and 12 h refeeding was 0·96±0·76 and 0·82 ± 0·50 mg·g wet wt ¹, respectively, as opposed to 0·21 ± 0·12 mg·g wet wt ¹ in the 21-days fasted fish. At the same time, activities of glycogen phosphorylase in the muscle and liver increased while the active‘I’form of glycogen synthetase showed higher activity in the liver. Since glycogen was resynthesized upon refeeding, this eliminated the possibility that glycogen depletion during starvation was due to stress or physical exhaustion after handling by the investigator. Throughout the experimental starvation period, the body weight of the mudskipper decreased, with a maximum of 12% weight loss after 21 days. Liver lipid reserves were utilized at the onset of fasting but were thereafter resynthesized. Muscle proteins were also metabolized as the fish were visibly thinner. However, no apparent change in protein content expressed as per gram wet weight was detected as the tissue hydration state was maintained constant. The increased degradation of liver and muscle reserves was coupled to an increase in the activities of key gluconeogenic enzymes in the liver (G6Pase, FDPase, PEPCK, MDH and PC). The increase in glucose synthesis was possibly necessary to counteract hypoglycemia brought about by starvation in B. boddaerti.     

Effect of cadmium on survival,osmoregulation and gill structure of the Sunda prawn,Macrobrachium sintangense (de Man), at different salinities

The prawn Macrobrachium sintangense is likely to be subjected to occasional exposure to combined metal and saline stressors in its natural environment. This research evaluated the acute toxicity (96?h LC₅₀) of cadmium (Cd) on the prawn M. sintangense, with respect to the osmoregulatory capacity (OC) of prawns and to document histological changes in the gills after exposure to sublethal Cd concentrations at different salinities. The 96?h LC₅₀ of Cd to M. sintangense decreased with increasing salinity. The 96?h LC₅₀ values were 89.12 (72.53–109.50), 681.26 (554.20–837.46) and 825.37 (676.99–1006.27) μg CdL^?1 at 0, 10 and 20 ppt, respectively. The OC of prawns exposed to 30?μg?CdL^?1 at 0 ppt and to 300?μg?CdL^?1 at10 ppt decreased significantly compared with that of control prawns exposed to 0 and 10 ppt respectively. Swelling, hyperplasia and necrosis of gill lamellae resulting in the loss of marginal canals were observed in the gills of prawns exposed to 30?μg?CdL^?1 at 0 ppt and to 300?μg?CdL^?1 at 10 ppt for 7?days.     

Glucose, pyruvate and lactate efflux by the perfused liver of a teleost, Clarias batrachus during aniso-osmotic exposure

Glucose, lactate and pyruvate efflux by the perfused liver of the walking catfish, Clarias batrachus was studied during aniso-osmotic exposure. During hypo-osmotic exposure (−80 mOsmol l⁻¹, maintained with NaCl), glucose, lactate and pyruvate efflux by the perfused liver significantly decreased by 55, 19 and 16%, respectively. During hyper-osmotic exposure (+80 mOsmol l⁻¹, maintained with NaCl), efflux increased by 57, 12 and 18%, respectively. Similar effects of glucose, lactate and pyruvate efflux by the perfused liver was also seen when the anisotonicity of the medium was adjusted with mannitol instead of NaCl. The decrease of glucose, lactate and pyruvate efflux during hypo-osmotic exposure was correlated with the stimulation of glycogen synthesis and the reverse was true during hyper-osmotic exposure. These observations were supported by changes in glycogen phosphorylase a (GPase a) and glycogen synthase a (GSase a) activities. During hypo-osmotic exposure (−80 mOsmol l⁻¹), the GPase a activity decreased by 1.93 fold and GSase a activity increased by 1.63 fold, while during hyper-osmotic exposure (+80 mOsmol l⁻¹), the GPase a activity increased by 1.58 fold and GSase a activity decreased by 1.95 fold. The total activity of both the enzymes were not effected by a short term exposure to aniso-osmotic conditions, suggesting that the alterations in GPase a and GSase a activity were mainly due to changes of their phosphorylation status during aniso-osmotic exposure. A direct correlation exists between glucose efflux and the hydration status of the perfused liver. These alterations of glucose metabolism are probably necessary by this walking catfish to meet the different energy demand, and also for maintenance of glucose homeostasis under osmotic stress.     

Functional differentiation in the anterior gills of the aquatic air-breathing fish, <Emphasis Type="Italic">Trichogaster leeri</Emphasis>

The fish gill is a multifunctional organ responsible for gas exchange and ionic regulation. It is hypothesized that both morphological and functional differentiation can be found in the gills of the aquatic air-breathing fish, Trichogaster leeri. To test this, we used the air-breathing fish, Trichogaster leeri, to investigate various morphological/functional parameters. First, we evaluated the importance of performing the aquatic surface respiration behavior in T. leeri. A reduced survival rate was observed when fish were kept in the restrained cages in hypoxic conditions. On the gross anatomy of gills, we found evidence of both morphological and functional modification in the first and the second gills and are responsible for ionic regulation. There were large-bore arterioarterial shunts in the fourth gill arch. It is specialized for the transport of oxygenated blood and is less responsive to environmental stress. In addition, the anterior and the posterior gills differed in the Na⁺, K⁺-ATPase activity upon ionic stresses. That is, only the Na⁺, K⁺-ATPase activity of the anterior two gills was up-regulated significantly in the deionized water. Lastly, we found that the number of mitochondria-rich cells in the first and the second gills increased following ionic stress and no difference was found in the third and the fourth gills following such an exposure. These results supported the hypothesis that there are morphological and functional differences between anterior and posterior gill arches within the air-breathing Trichogaster leeri. In contrast, no significant difference was found among gills in gross anatomy, filament density and Na⁺, K⁺-ATPase activity in the non-air-breather, Barbodes schwanenfeldi.     

Zn Subcellular Distribution in Liver of Goldfish (Carassius Auratus) with Exposure to Zinc Oxide Nanoparticles and Mechanism of Hepatic Detoxification

Zinc Oxide Nanoparticles (ZnO NPs) have attracted increasing concerns because of their widespread use and toxic potential. In this study, Zn accumulations in different tissues (gills, liver, muscle, and gut) of goldfish (Carassius auratus) after exposure to ZnO NPs were studied in comparison with bulk ZnO and Zn²⁺. And the technique of subcellular partitioning was firstly used on the liver of goldfish to study the hepatic accumulation of ZnO NPs. The results showed that at sublethal Zn concentration (2 mg/L), bioaccumulation in goldfish was tissue-specific and dependent on the exposure materials. Compared with Zn²⁺, the particles of bulk ZnO and the ZnO NPs appeared to aggregate in the environmentally contacted tissues (gills and gut), rather than transport to the internal tissues (liver and muscle). The subcellular distributions of liver differed for the three exposure treatments. After ZnO NPs exposure, Zn percentage in metal-rich granule (MRG) increased significantly, and after Zn²⁺ exposure, it increased significantly in the organelles. Metallothionein-like proteins (MTLP) were the main target for Zn²⁺, while MRG played dominant role for ZnO NPs. The different results of subcellular distributions revealed that metal detoxification mechanisms of liver for ZnO NPs, bulk ZnO, and Zn²⁺ were different. Overall, subcellular partitioning provided an interesting start to better understanding of the toxicity of nano- and conventional materials.