Dietary lecithin potentiates thermal tolerance and cellular stress protection of milk fish (Chanos Chanos) reared under low dose endosulfan-induced stress

Endosulfan is an organochlorine pesticide commonly found in aquatic environments that has been found to reduce thermal tolerance of fish. Lipotropes such as the food additive, Lecithin has been shown to improve thermal tolerance in fish species. This study was conducted to evaluate the role of lipotropes (lecithin) for enhancing the thermal tolerance of Chanos chanos reared under sublethal low dose endosulfan-induced stress. Two hundred and twenty-five fish were distributed randomly into five treatments, each with three replicates. Four isocaloric and isonitrogenous diets were prepared with graded levels of lecithin: normal water and fed with control diet (En0/L0), endosulfan-treated water and fed with control diet (En/L0), endosulfan-treated water and fed with 1% (En/L1%), 1.5% (En/L 1.5%) and 2% (En/L 2%) lecithin supplemented feed. The endosulfan in treated water was maintained at the level of 1/40th of LC₅₀ (0.52 ppb). At the end of the five weeks, critical temperature maxima (CTmax), lethal temperature maxima (LTmax), critical temperature minima (CTmin) and lethal temperature minima (LTmin) were Determined. There was a significant (P<0.01) effect of dietary lecithin on temperature tolerance (CTmax, LTmax, CTmin and LTmin) of the groups fed with 1, 1.5 and 2% lecithin-supplemented diet compared to control and endosulfan-exposed groups. Positive correlations were observed between CT max and LTmax (R²=0.934) as well as between CTmin and LTmin (R²=0.9313). At the end of the thermal tolerance study, endosulfan-induced changes in cellular stress enzymes (Catalase, SOD and GST in liver and gill and neurotansmitter enzyme, brain AChE) were significantly (p<0.01) improved by dietary lecithin. We herein report the role of lecithin in enhancing the thermal tolerance and protection against cellular stress in fish exposed to an organochlorine pesticide.     

Lipotropes promote immunobiochemical plasticity and protect fish against low-dose pesticide-induced oxidative stress

An experiment was conducted to evaluate the role of different lipotropes in modulating immunity and biochemical plasticity under conditions of sublethal low-dose pesticide-induced stress in fish. Labeo rohita fish fingerlings were divided in two sets with one set of fish continuously exposed to low-dose endosulfan (1/10th of 96-h LC₅₀) for 21 days, the other was unexposed, and both sets of fish were fed with practical diets supplemented with either 2 % lecithin, 0.5 % betaine, or 0.1 % choline and compared against unsupplemented diet. Low-dose endosulfan exposure had adverse effects (P < 0.05/P < 0.01) on hematological profile (erythrocyte count, hemoglobin, and hematocrit), serum protein (total protein, albumin, and globulin) and lipid profile (cholesterol and triglyceride), anti-oxidative status (ascorbic acid content of muscle, liver, brain, and kidney and activity of anti-oxidative enzymes: catalase and superoxide dismutase), neurotransmission (acetylcholinesterase activity in muscle and brain), immunological attributes (WBC count, albumin to globulin ratio, phagocytic activity, and serum cortisol), and metabolic plasticity as revealed from enzyme activities (muscle lactate dehydrogenase, liver and kidney glucose-6-phosphatase dehydrogenase-G6PDH activity). Dietary lipotropes prevented these effects completely or partially and the effects were lipotrope dependent. Kinetics (maximum velocity value V_max, catalytic efficiency and Michaelis constant K_m) of G6PDH enzyme from crude extracts of liver and kidney indicated inhibition due to endosulfan but lipotropes could protect enzyme and showed a stabilizing effect. The supplements also helped maintain integrity of histoarchitecture of the hepatocytes in endosulfan-exposed fish to a great extent. Feeding lipotropes to fish reared in endosulfan-free water also improved hematological and serum protein and lipid profiles and were immunostimulatory. In conclusion, dietary lipotropes, especially betaine and lecithin at the levels used, improve erythropoiesis, serum protein and lipid profile, anti-oxidant status, immunocompetence, neurotransmission, and protect the livers of L. rohita fingerlings even when continuously exposed to low-dose endosulfan.     

Sub-lethal effect of synthetic pyrethroid pesticide on metabolic enzymes and protein profile of non-target Zebra fish,Danio rerio

Extensive application of pesticide in agricultural field affects the enzymatic activity of non-target animals, including fishes. In this study, the impact of sublethal concentration of fenvalerate on marker enzymes of freshwater Zebra fish was evaluated. Pesticide-induced stress can specifically affect non target fishes, through elevated level of reactive oxygen species which is responsible for biochemical, cell metabolism and physiological activities. The oxidative stress mediated by fenvalerate at sub lethal concentrations after 28 days of exposure of Zebra fish. Following 28 days of exposure of pesticide, catalase, superoxide dismutase, aspartate amino transferases, alanine amino transferase, alkaline phosphatase and acid phosphatase were assessed. Results revealed reduction of superoxide dismutase activity after 28 days of exposure in sub lethal concentration of fenvalerate in liver and gills. In liver, catalase activity was found to be less in fenvalerate exposed fish than control fish. In liver, increase of 75.75% aspartate amino transferase and 38% increase in alanine amino transferase in gills. SGPT activity was relatively higher than SGOT suggests more contribution of phyruvalate than oxaloacetate formation. Fenvalerate induced changes in acid phosphatase and alkaline phosphatase activity in the liver and gills of Zebra fish after four weeks of exposure. Fenvalerate induced expression of various stress proteins in gill, liver, followed by muscle. Some proteins lost its intensity due to fenvalerate toxicity. Result revealed that enzyme assays and SDS-PAGE analysis for protein subunits determination is relevant tool to monitor stress in freshwater ecosystem. The findings suggest that in monitoring fenvalerate toxicity programme, enzyme activities can be potent diagnostic tool for fenvalerate induced toxicity.     

Shifts in small-bodied fish assemblages resulting from drought-induced water level recession in terminating lakes of the Murray-Darling Basin, Australia

Over-abstraction of water places unsustainable pressures on river ecosystems, with the impacts amplified under drought conditions. Freshwater fishes are particularly vulnerable due to associated changes in water quality, and habitat availability, condition and connectivity. Accordingly, fish assemblages are ideal indicators of the impacts of drought and over-abstraction. The Murray-Darling Basin (MDB), south-eastern Australia, terminates at the Ramsar listed Coorong and Lower Lakes, which comprise Lake Alexandrina and Lake Albert. Over-abstraction and extreme drought during the last decade has placed these lakes under severe environmental stress. The purpose of this study was to investigate shifts in fish assemblages caused by substantial water level recession and salinization in the Lower Lakes. Small-bodied fish assemblages were sampled at the beginning and several years into the drought. Off-lake habitats held diverse fish assemblages in 2003, but most sites were dry by 2009. Remaining habitats were disconnected, salinities increased substantially, and aquatic vegetation shifted from freshwater to salt-tolerant species. There was a substantial decline in the proportion of specialist species, especially diadromous and threatened species, and an emerging dominance of generalist freshwater and estuarine species. The findings warn of the inevitable ecological impact of over-allocating water for human use in drought-prone regions, and highlight the need for adequate environmental water allocations. This study also emphasises that understanding the ecological attributes of a fish species, and the subsequent assignment to a functional group, will help predict vulnerability to decline and extirpation.     

From Ethnobiology to Ecotoxicology: Fishers’ Knowledge on Trophic Levels as Indicator of Bioaccumulation in Tropical Marine and Freshwater Fishes

Information on fish trophic levels is important to assess fishing impacts and to better understand the bioaccumulation of pollutants within aquatic food chains. The local ecological knowledge held by small-scale fishers can fill knowledge gaps in fish trophic ecology. We estimated the trophic levels of 69 tropical and subtropical fish species (33 coastal and 36 freshwater species) using data on fish diets from the literature and obtained from interviews with Brazilian fishers. The fish trophic levels estimated from fishers’ knowledge were positively correlated with the trophic levels estimated using data from biological studies for both coastal and freshwater fish. The fishers’ knowledge also indicated bioaccumulation patterns, as the fish trophic levels estimated from fishers’ knowledge were positively related to the mercury (Hg) content in fish muscle (wet weight, from literature data) in 41 fish species (15 coastal and 26 freshwater). These findings reveal the potential for new applications of fishers’ knowledge to ecotoxicology, which could improve management of aquatic ecosystems and strengthen fishers’ political status.     

The effects of ultraviolet radiation on a freshwater prey fish: physiological stress response,club cell investment,and alarm cue production

Recent anthropogenic activities have caused deleterious effects to the stratospheric ozone layer, resulting in a global increase in the level of ultraviolet radiation (UVR). Understanding the way that organisms respond to such stressors is key to predicting the effects of anthropogenic activities on aquatic ecosystems and the species that inhabit them. The epidermal layer of the skin of fishes is not keratinized and acts as the primary interface between the fish and its environment. The skin of many species of fishes contains large epidermal club cells (ECCs) that are known to release chemicals (alarm cues) serving to warn other fishes of danger. However, the alarm role of the cells is likely secondary to their role in the immune system. Recent research suggests that ECCs in the epidermis may play a role in protecting the fish from damage caused by UVR. In the present study, we examined the effects of in vivo exposure to UVR on fathead minnows (Pimephales promelas), specifically investigating ECC investment, physiological stress responses, and alarm cue production. We found that fish exposed to UVR showed an increase in cortisol levels and a substantive decrease in ECC investment compared to non‐exposed controls. Unexpectedly, our subsequent analysis of the behavioural response of fish to alarm cues revealed no difference in the potency of the cues prepared from the skin of UV‐exposed or non‐exposed minnows. Our results indicate that, although nonlethal, UVR exposure may lead to secondary mortality by altering the fish immune system, although this same exposure may have little influence on chemically‐mediated predator–prey interactions. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, 105 , 832–841.     

Pervasive decline of subtropical aquatic insects over 20 years driven by water transparency,non-native fish and stoichiometric imbalance

Insect abundance and diversity are declining worldwide. Although recent research found freshwater insect populations to be increasing in some regions, there is a critical lack of data from tropical and subtropical regions. Here, we examine a 20-year monitoring dataset of freshwater insects from a subtropical floodplain comprising a diverse suite of rivers, shallow lakes, channels and backwaters. We found a pervasive decline in abundance of all major insect orders (Odonata, Ephemeroptera, Trichoptera, Megaloptera, Coleoptera, Hemiptera and Diptera) and families, regardless of their functional role or body size. Similarly, Chironomidae species richness decreased over the same time period. The main drivers of this pervasive insect decline were increased concurrent invasions of non-native insectivorous fish, water transparency and changes to water stoichiometry (i.e. N : P ratios) over time. All these drivers represent human impacts caused by reservoir construction. This work sheds light on the importance of long-term studies for a deeper understanding of human-induced impacts on aquatic insects. We highlight that extended anthropogenic impact monitoring and mitigation actions are pivotal in maintaining freshwater ecosystem integrity.     

Elevation of C-reactive protein in serum of Channa punctatus as an indicator of water pollution.

Effect of some pollutants like heavy metals, non-metals and pesticides on the circulating level of C-reactive protein (CRP) which is an acute phase plasma protein was studied in a freshwater murrel C. punctatus. Fish was exposed to nonlethal doses of these xenobiotics which were apparently safe. But the level of CRP detected by sensitive single radial immunodiffusion (SRID) technique showed that within 12 hr of exposure the nonlethal doses of xenobiotics could initiate the acute phase response in terms of elevated CRP titre. Heavy metals caused the acute phase within 24 hr, nonmetals and Metacid-50 within 48 hr exposure. The carbamate compound, carbaryl demonstrated a biphasic response to CRP level which may be correlated with the reversible type of anticholinesterase property of this compound while Metacid-50 is an irreversible type of anticholinesterase agent. The assessment of the CRP level in the serum of fish may be utilized as a primary bioindicator of a contaminated environment toxic enough to mount an acute phase response.     

Comparative approaches to understand metal bioaccumulation in aquatic animals

Over the past decades, comparative physiology and biochemistry approaches have played a significant role in understanding the complexity of metal bioaccumulation in aquatic animals. Such a comparative approach is now further aided by the biokinetic modeling approach which can be used to predict the rates and routes of metal bioaccumulation and assist in the interpretation of accumulated body metal concentrations in aquatic animals. In this review, we illustrate a few examples of using the combined comparative and biokinetic modeling approaches to further our understanding of metal accumulation in aquatic animals. We highlight recent studies on the different accumulation patterns of metals in different species of invertebrates and fish, and between various aquatic systems (freshwater and marine). Comparative metal biokinetics can explain the differences in metal bioaccumulation among bivalves, although it is still difficult to explain the evolutionary basis for the different accumulated metal body concentrations (e.g., why some species have high metal concentrations). Both physiological/biochemical responses and metal geochemistry are responsible for the differences in metal concentrations observed in different populations of aquatic species, or between freshwater and marine species. A comparative approach is especially important for metal biology research, due to the very complicated and potentially variable physiological handling of metals during their accumulation, sequestration, distribution and elimination in different aquatic species or between different aquatic systems.     

Channa punctata brain metallothionein is a potent scavenger of superoxide radicals and prevents hydroxyl radical-induced in vitro DNA damage

Mammalian brain metallothioneins (MTs) have been shown to scavenge free radicals. However, a similar role for fish brain MT has not been established yet. Previously, we have reported that MT from the liver of a freshwater fish, Channa punctata Bloch, had free-radical-scavenging activity in vitro. In this study, we report on the induction of MT in brain and other tissues of C. punctata treated with a low concentration of zinc chloride. We partially purified MT (Zn-MT)-rich fraction from the brain and studied its free-radical-scavenging and DNA damage attenuating effects. Zinc exposure showed significant MT induction in brain, gill, kidney, and liver. C. punctata brain MT efficiently scavenged superoxide radicals and also attenuated hydroxyl radical-mediated DNA damage. These findings suggest that fish brain MT has a free-radical-scavenging activity, and its expression may be regulated in response to stress and chemical exposure. C. punctata has been identified as a potent biomarker fish species. It is suggested that this fish species may be a good model for the study of MTs with regard to their regulatory and biomarker functions.     

The interactive effect of elevated temperature on deltamethrin-induced biochemical stress responses in Channa punctata Bloch

There are reports showing interactive effect of environmental factors with the toxic outcome of chemicals. We studied the interactive effect of elevated temperature as an abiotic stressor on deltamethrin-induced biochemical stress responses in a freshwater fish, Channa punctata Bloch. Heat stress (∼12 °C above ambient temperature for 3 h) and pesticide exposure (deltamethrin 0.75 ppb for 48 h) showed significant induction of heat shock protein-70 (HSP70) in liver, kidney and gills of fishes. Elevated temperature when followed by deltamethrin exposure showed synergistic effect showing a high level of HSP70 in liver and gills whereas response in the kidney was opposite. On the contrary, when deltamethrin exposure followed the heat stress, no significant difference was observed. Protein carbonylation was found to be more pronounced in heat-stressed group compared with control fish group. A significant increase in lipid peroxidation (LPO) was observed in different tissues of fish exposed to either of the stressors. In the kidney of fish exposed to heat stress followed by deltamethrin, LPO was relatively lower as compared to other treatments. Thiols content such as reduced glutathione (GSH), total thiols (T-SH), non-protein thiols (NP-SH) and protein thiols (P-SH) showed no consistent pattern in different tissues. In deltamethrin-exposed group that was subsequently exposed to heat stress, the GSH content was higher in liver and lower in both kidney and gills when compared with other groups. Alteration in the activities of antioxidant enzymes such as catalase (CAT), glutathione S-transferase (GST), glutathione reductase (GR) and glutathione peroxidase (GPx) was also observed when fish were exposed to heat stress and/or deltamethrin. Our study demonstrated that heat stress modulated biochemical stress responses in fish showing a tissue specific pattern. This implies that fish has the capacity to elicit differential response to exposure to abiotic stressors in order to reduce the systemic magnitude of stress which may otherwise lead to severe dysfunction of vital tissues.     

Effect of extremely low frequency electromagnetic field on brain histopathology of Caspian Sea Cyprinus carpio

There is limited research on the effect of electromagnetic field on aquatic organisms, especially freshwater fish species. This study was conducted to evaluate the effect of extremely low frequency electromagnetic field (ELF-EMF) (50 Hz) exposure on brain histopathology of Cyprinus carpio, one of the important species of Caspian Sea with significant economic value. A total of 200 healthy fish were used in this study. They were classified randomly in two groups: sham-exposed group and experimental group, which were exposed to five different magnetic field intensities (0.1, 1, 3, 5, and 7 mT) at two different exposure times (0.5 and 1 h). Histologic results indicate that exposure of C. carpio to artificial ELF-EMF caused severe histopathological changes in the brain at field intensities ≥3 mT leading to brain necrosis. Field intensity and duration of exposure were key parameters in induction of lesion in the brain. Further studies are needed to elucidate exact mechanism of EMF exposure on the brain.     

Cadmium,chromium, and lead accumulation in aquatic plants and animals near a municipal landfill

This research was conducted to assess the contamination of heavy metals in the water, sediment, aquatic plants and animals around a municipal landfill. The heavy metals were analyzed by inductively coupled plasma optical emission spectrometry (ICP-OES). The concentrations of cadmium (Cd), chromium (Cr), and lead (Pb) in water and sediment were Not detected (ND), 0.05 ± 0.98, and 0.02 ± 0.01 mg/L; and 0.47 ± 0.23, 18.65 ± 11.39, and 5.36 ± 2.08 mg/kg, respectively. A total of 24 aquatic plants from 4 species were collected from the municipal landfill. Cd concentrations in all plant species were within the standard, while Cr and Pb exceeded the standard. Forty-four fish from 4 species, 29 freshwater snails from 3 species, 10 freshwater prawns from 1 species, and 9 freshwater crabs from 1 species were collected. Cd and Cr concentrations in 2 species of fish samples exceeded the standard and Pb concentration in all fish species exceeded the standard. Cd and Pb concentrations in all freshwater snails were within the standard, except Cr. Meanwhile, Cd and Pb in freshwater prawns and snails were within the standard, except Cr. Five species of frogs were collected. Cd and Cr concentrations in 2 species exceeded the standard. Pb concentrations in all frog species exceeded the standard. The pattern of metal accumulation was fish > frogs > freshwater snails > freshwater prawns = freshwater crab (Cd), freshwater prawn > frogs > freshwater crab = freshwater snail > fish (Cr), and freshwater prawn > fish > frogs > freshwater snail > freshwater crab (Pb).     

Impact of terrestrial protected areas on the fish diversity and habitat quality: Evidence from tropical river Pranhita,India

The conservation and management of inland fish and freshwater ecosystems immensely contribute to global sustainable development. The existing ‘Protected Area’ (PA) network does not represent freshwater resources well and seldom considers its fish communities, while designating PAs. A study was undertaken to quantitatively assess the role played by the three terrestrial PAs (IUCN category IV) in conserving fish diversity and preserving habitat quality in the river reaches bordering the three PAs of the river Pranhita. It is a unique river system in the Indian Deccan Plateau in terms of fish diversity and community structure. Field surveys were conducted during the non-monsoon and monsoon seasons in 2020–21, that recorded 53 species including endemic and threatened fishes from river Pranhita, which represent more than one-third the number of fish species of Telangana state. The higher diversity and lower dominance index value (p < 0.01) reported in PAs compared to Eco Sensitive Zones and unprotected areas during the non-monsoon season indicate the role of intact physical habitat in providing refuges to the fish species in monsoon dependent tropical rivers. The optimal water quality revealed no significant difference (p > 0.0001) between protected and unprotected river reaches, and healthy biotic integrity assessed on the basis of fish community structure was attributed to the contiguous flow and less anthropogenic disturbance. This study supports that it can be considered as a representative zone for the conservation and protection of indigenous and endemic fish species of the Godavari Basin. The results concluded that the scope of the terrestrial PA network in India could be potentially extended to their bordering aquatic ecosystems, especially rivers to maintain pristine habitat conditions and conserve the fish genetic resources to ensure the flow of ecosystem services.     

草甘膦对草鱼、鲢鱼和鲫鱼的毒性

【背景】草甘膦是一种灭生性除草剂,对防治多年生杂草效果明显。近年来,草甘膦被广泛用于防治鱼塘水生杂草,其对鱼类的安全性逐渐受到关注。【方法】采用半静态法测试了草甘膦对草鱼、鲢鱼和鲫鱼的急性毒性,并计算出其对草鱼、鲢鱼和鲫鱼的安全浓度。【结果】随着受试鱼苗在药液中暴露时间的延长,LG50值逐渐减小;草甘膦对草鱼、鲢鱼和鲫鱼的96h LC50值分别为0．2518、0．2588和0．2599mg·L^-1;草甘膦对草鱼、鲢鱼和鲫鱼的安全浓度分别为0．0252、0．0259和0．0260mg·L^-1。【结论与意义】草甘膦对草鱼、鲢鱼和鲫鱼高毒,该结果对指导淡水养殖区杂草防除时科学使用草甘膦具有重要的实践意义。     

Disease and pollution alter Daphnia taxonomic and clonal structure in experimental assemblages

1. Environmental stressors can influence population and community structure. However, the majority of experimental work on multiple environmental stressors has been done at the individual level only. 2. In this work, we followed changes in experimental assemblages of Daphnia (waterfleas; consisting of two taxa and three clones per taxon) after exposure to the fungal parasite Metschnikowia sp. and/or the pesticide diazinon. 3. We found a significant shift in taxonomic and clonal composition under both stressors. Strikingly, in the parasite and parasite + pesticide treatments, one taxon went extinct. While the pesticide had no effect on total parasite prevalence, the taxon that was more susceptible to extinction was, at the same time, more infected when additionally exposed to the pesticide. Furthermore, the density of all adult females was significantly reduced in the parasite treatment, but not in the pesticide treatment. 4. Our results demonstrate that the dynamics of Daphnia assemblages are altered by parasites and pesticide exposure. Given the key role of Daphnia in aquatic food webs in transferring primary production into fish food, this could be of wide significance in aquatic ecosystems.     

DO FRESHWATER FISHES DIVERSIFY FASTER THAN MARINE FISHES? A TEST USING STATE‐DEPENDENT DIVERSIFICATION ANALYSES AND MOLECULAR PHYLOGENETICS OF NEW WORLD SILVERSIDES (ATHERINOPSIDAE)

Freshwater habitats make up only ～0.01% of available aquatic habitat and yet harbor 40% of all fish species, whereas marine habitats comprise >99% of available aquatic habitat and have only 60% of fish species. One possible explanation for this pattern is that diversification rates are higher in freshwater habitats than in marine habitats. We investigated diversification in marine and freshwater lineages in the New World silverside fish clade Menidiinae (Teleostei, Atherinopsidae). Using a time‐calibrated phylogeny and a state‐dependent speciation–extinction framework, we determined the frequency and timing of habitat transitions in Menidiinae and tested for differences in diversification parameters between marine and freshwater lineages. We found that Menidiinae is an ancestrally marine lineage that independently colonized freshwater habitats four times followed by three reversals to the marine environment. Our state‐dependent diversification analyses showed that freshwater lineages have higher speciation and extinction rates than marine lineages. Net diversification rates were higher (but not significant) in freshwater than marine environments. The marine lineage‐through time (LTT) plot shows constant accumulation, suggesting that ecological limits to clade growth have not slowed diversification in marine lineages. Freshwater lineages exhibited an upturn near the recent in their LTT plot, which is consistent with our estimates of high background extinction rates. All sequence data are currently being archived on Genbank and phylogenetic trees archived on Treebase.     

DNA adducts in marine and freshwater fish as biomarkers of environmental contamination

The analysis of DNA modifications in aquatic animals may serve as a sensitive marker of exposure to genotoxic contaminants. This is of importance in assessing water quality regarding pollution with genotoxic compounds, food safety analysing edible aquatic animals and in terms of ecotoxicology. Covalent modification of DNA is considered a crucial event in chemical carcinogenesis and thus may be considered a biomarker of an early genotoxic effect. Measuring DNA adducts is unique in that these lesions may be considered a biomarker of both exposure and effect. A number of studies have described the analysis of the DNA isolated from the liver of both freshwater and marine fish. Considerable levels of DNA adducts have been observed in some animals from contaminated lakes or rivers. Low levels were observed in DNA from the liver of marine fish. The background levels of DNA adducts have to be determined in animals from appropriate uncontaminated control sites that are matched for species, gender, age and season of the year. It is of crucial importance to consider the species analysed since there have been reports of the non responsiveness of some species.     

Intraspecific variation in the growth and survival of juvenile fish exposed to Eucalyptus leachate

Whilst changes in freshwater assemblages along gradients of environmental stress have been relatively well studied, we know far less about intraspecific variation to these same stressors. A stressor common in fresh waters worldwide is leachates from terrestrial plants. Leachates alter the physiochemical environment of fresh waters by lowering pH and dissolved oxygen and also releasing toxic compounds such as polyphenols and tannins, all of which can be detrimental to aquatic organisms. We investigated how chronic exposure to Eucalyptus leaf leachate affected the growth and survival of juvenile southern pygmy perch (Nannoperca australis) collected from three populations with different litter inputs, hydrology and observed leachate concentrations. Chronic exposure to elevated leachate levels negatively impacted growth and survival, but the magnitude of these lethal and sublethal responses was conditional on body size and source population. Bigger fish had increased survival at high leachate levels but overall slower growth rates. Body size also varied among populations and fish from the population exposed to the lowest natural leachate concentrations had the highest average stress tolerance. Significant intraspecific variation in both growth and survival caused by Eucalyptus leachate exposure indicates that the magnitude (but not direction) of these stress responses varies across the landscape. This raises the potential for leachate‐induced selection to operate at an among‐population scale. The importance of body size demonstrates that the timing of leachate exposure during ontogeny is central in determining the magnitude of biological response, with early life stages being most vulnerable. Overall, we demonstrate that Eucalyptus leachates are prevalent and potent selective agents that can trigger important sublethal impacts, beyond those associated with more familiar fish kills, and reiterate that dissolved organic carbon is more than just an energy source in aquatic environments.     

Arsenobetaine in Atlantic salmon (Salmo salar L.): influence of seawater adaptation

Glycine betaine has been suggested to improve the maintenance of ionic and osmotic homeostasis during seawater adaptation in teleost fish. Arsenobetaine may also behave as an osmolyte, due to its structural similarity to glycine betaine. The influence of seawater adaptation on intestinal uptake and muscle accumulation of arsenobetaine in the teleost Atlantic salmon (Salmo salar L.) was investigated. Atlantic salmon (freshwater and seawater adapted) were given a single oral dose of arsenobetaine, which was absorbed over the intestine within 6 h after exposure. Seawater adapted Atlantic salmon had significantly higher levels of accumulated arsenobetaine in blood compared to the freshwater adapted salmon. However, seawater adaptation had no effect on the levels of accumulated arsenobetaine in muscle tissue. Similar retention of the administered dose was found in muscle tissue in both freshwater and seawater adapted salmon, with 49+/-6% and 50+/-10% retention after 144 h, respectively. Results indicate that muscle retention was not influenced by salinity in seawater adapting teleosts.