A note on copper bioaccumulation in Mozambique tilapia,Oreochromis mossambicus (Osteichthyes: Cichlidae)

Copper (Cu) is one of the most commonly reported metal pollutants in African water bodies, but there are few studies on African freshwater fish species of copper accumulation and copper toxicity. Adult O. mossambicus were exposed to 0mg l^?1 (control) and 0.75mg l^?1 Cu for 96h and 0 (control), 0.11, 0.29 and 0.47mg l^?1 copper for 64 days. Samples of liver and gills were collected after 96h, and after 1, 32 and 64 days, respectively. There were significant differences in the mean Cu accumulation values in the liver and gills between the control and the Cu-exposed fish after the 96-h exposure. In fish exposed to 0.11 and 0.29mg l^?1 Cu for 64 days there was an increase in copper level in the tissues. In fish exposed to 0.47mg l^?1 Cu the concentration in the gill and liver tissue did not increase between Day 1 and Day 32. At this time, Cu accumulation in the liver was higher than for fish exposed to 0.11 and 0.29mg l^?1 Cu for 64 days. Exposure to approximately 0.47mg l^?1 Cu for more than 32 days induced mortality.     

Impact of anthropogenic disturbances on a diverse riverine fish assemblage in Fiji predicted by functional traits

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Efficiency of Neutral Red,Evans Blue and MTT to assess viability of the freshwater microalgae Desmodesmus communis and Pediastrum boryanum

This study assessed the efficacy of three cell viability assays – Methyl‐thiazolyl‐tetrazolium (MTT), Evans Blue, and Neutral Red – for two freshwater microalgae species, Desmodesmus communis and Pediastrum boryanum (Chlorophyceae), in order to find suitable techniques to detect the levels of pollution in water ecosystems. Following exposure to a glyphosate‐based herbicide, our results showed that Evans Blue did not adequately measure cell viability in either species, while MTT and Neutral Red were able to detect decreased cellular viability for both algae in response to herbicide exposure. Overall, however, Neutral Red proved to be more sensitive than MTT for these algae.     

Predictive Value of Species Sensitivity Distributions for Effects of Herbicides in Freshwater Ecosystems

In this article we present a review of the laboratory and field toxicity of herbicides to aquatic ecosystems. Single-species acute toxicity data and (micro)mesocosm data were collated for nine herbicides. These data were used to investigate the importance of test species selection in constructing species sensitivity distributions (SSDs), and in estimating hazardous concentrations (i.e., HC5) protective for freshwater aquatic ecosystems. A lognormal model was fitted to toxicity data (acute EC50s and chronic NOECs) and the resulting distribution used to estimate lower (95% confidence), median (50% confidence), and upper (5% confidence), HC5 values. The taxonomic composition of the species assemblage used to construct the SSD does have a significant influence on the assessment of hazard and only sensitive primary producers should be included for the risk assessment of herbicides. No systematic difference in sensitivity between standard and non-standard test species was observed. Hazardous concentrations estimated using laboratory-derived acute and chronic toxicity data for sensitive freshwater primary producers were compared to the response of herbicide-stressed freshwater ecosystems using a similar exposure regime. The lower limit of the acute HC5 and the median value of the chronic HC5 were protective of adverse effects in aquatic micro/mesocosms even under a long-term exposure regime. The median HC5 estimate based on acute data was protective of adverse ecological effects in freshwater ecosystems when a pulsed or short-term exposure regime was used in the microcosm and mesocosm experiments. There was also concordance between the predictions from the effect model PERPEST and the concentrations at which clear effects started to emerge in laboratory and field studies. However, compared to the SSD concept, the PERPEST model is able to provide more information on ecological risks when a common toxicological mode of action is evaluated as it considers both recovery and indirect effects.     

Variations in renal morphology during adaptation to salinities in tilapias

Synopsis Fifteen days oldOreochromis niloticus andO. mossambicus juveniles were gradually adapted to 10, 20, 30 and 35 ppt sea water. Kidney morphology was observed after transfer to higher salinities and compared with freshwater controls. Despite differences in salinity tolerance, both species have similar transformations when transferred at high salinity, particularly reduction of the glomerular area after 2 months adaptation to sea water, and change in tubule morphology.     

The interrelationships between stress and osmoregulation in a euryhaline fish, Oreochromis mossambicus

Three groups of Oreochromis mossambicus, progeny of a single couple, acclimated to freshwater, seawater and iso‐osmotic water, respectively, were confined for 4 h following the same experimental procedures. Confinement stress evoked a ‘simple’ stress response that produced a significant rise in cortisol and glucose and slight osmotic disturbances for each tested salinity. It was speculated that the mechanisms securing osmotic homeostasis in this extremely euryhaline species favour it from a wide osmotic stress‐evoked disturbance.     

Toxicological Assessment of Arsenic-Induced Hematological Alterations and Chromosomal Aberrations in Tilapia Oreochromis mossambicus

Arsenic is an environmental contaminant and potential carcinogen. Toxicological assessment of As, which causes hematological alterations and chromosomal aberrations, was studied in freshwater fish Oreochromis mossambicus. Fish were exposed to 3 ppm, 28 ppm, and 56 ppm concentrations of sodium arsenite (NaAsO₂) and blood samples were collected after 48 h, 96 h, and 192 h of exposure. Hematological assay of exposed fish revealed abnormal mature and immature erythrocytes, deformed erythrocytes (spindle-shaped and triangular erythrocytes) and erythrocytes with segmented nuclei in all treatments. Arsenic exposure induced chromosomal aberration in a concentration-dependent manner, whereas, a decreasing trend was found after 192 h exposure. Observations on blood cells of exposed fish revealed chromosome breaks, chromatid breaks, and chromatid gaps. The alterations and aberrations of these parameters can be effectively used to assess toxicological effects of As on fish in the aquatic environment and at the same time this study elucidates the potential risks to humans who live in arsenic-contaminated areas.     

Experimental studies on toxicity of zinc to a freshwater teleost,rasbora daniconius (Hamilton)

Rasbora daniconius (Ham.) were exposed to zinc sulphate upto 15 days under static bioassay test conditions with renewal of the test solutions every 24 hours. Simultaneously control fish were also kept in water without zinc. The 96 and 240 hr LC₅₀ values were 38.1 and 33.3 PPm of zinc respectively. A reduced mortality rate was observed after 96 hr and LC₅₀ approached a constant value at 240 hr of exposure to the toxicant. Fish showed abnormal behaviour, deposition of mucus and appearance of haemorrhage on the body in case of higher concentrations of zinc, before death. The reported LC₅₀ values in the present study were comparatively higher than those reported by earlier investigators.See offprint requests to: Dr. V. K. Rajbanshi, Department of Limnology and Fisheries, University of Udaipur, Udaipur-313001, India.     

Salinity tolerance of Great Lakes invaders

1. The Laurentian Great Lakes are among the most invaded freshwater ecosystems in the world. Historically, the major vector for the introduction of non‐indigenous species (NIS) has been the release of contaminated ballast water via transoceanic ships. Despite regulations implemented in 1993, requiring vessels carrying fresh ballast water to exchange this water with saline ocean water, new reports of invasions have continued. 2. NIS often have a wide environmental tolerance allowing them to adapt to and invade a variety of habitats. It has been hypothesized that NIS with broad salinity tolerance may be able to survive ballast water exchange (BWE) and continue to pose an invasion risk to the Great Lakes. 3. We tested the short‐term salinity tolerance of eight recent invaders to the Great Lakes, specifically three cladocera (Bosmina coregoni, Bythotrephes longimanus, Cercopagis pengoi), two molluscs (Dreissena polymorpha, Dreissena rostriformis bugensis), and one species each of the families Gammaridae, Mysidae and Gobidae (Echinogammarus ischnus, Hemimysis anomala, Neogobius melanostomus) to determine if they could have survived salinities associated with BWE. 4. Overall, short‐term exposure to highly saline water dramatically reduced survival of all species. Two different methods of BWE tested, simultaneous and sequential, were equally effective in reducing survival. Species that survived the longest in highly saline water either possess behavioural characteristics that reduce exposure to adverse environments (valve closure; both Dreissena species) or are reported to have some degree of salinity tolerance in their native region (Echinogammarus). Given that exposure in our trials lasted a maximum of 48 h, and that species in ballast tanks would typically be exposed to saline water for c. 5 days, it appears that BWE is an effective method to reduce the survival of these NIS. These results provide impetus for tightening policy and monitoring of BWE, in particular for ships entering the Great Lakes from freshwater ports.     

Salmonella spp., Vibrio spp., Clostridium perfringens, and Plesiomonas shigelloides in Marine and Freshwater Invertebrates from Coastal California Ecosystems

The coastal ecosystems of California are highly utilized by humans and animals, but the ecology of fecal bacteria at the land–sea interface is not well understood. This study evaluated the distribution of potentially pathogenic bacteria in invertebrates from linked marine, estuarine, and freshwater ecosystems in central California. A variety of filter-feeding clams, mussels, worms, and crab tissues were selectively cultured for Salmonella spp., Campylobacter spp., Escherichia coli-O157, Clostridium perfringens, Plesiomonas shigelloides, and Vibrio spp. A longitudinal study assessed environmental risk factors for detecting these bacterial species in sentinel mussel batches. Putative risk factors included mussel collection near higher risk areas for livestock or human sewage exposure, adjacent human population density, season, recent precipitation, water temperature, water type, bivalve type, and freshwater outflow exposure. Bacteria detected in invertebrates included Salmonella spp., C. perfringens, P. shigelloides, Vibrio cholerae, Vibrio parahaemolyticus, and Vibrio alginolyticus. Overall, 80% of mussel batches were culture positive for at least one of the bacterial species, although the pathogens Campylobacter, E. coli-O157, and Salmonella were not detected. Many of the same bacterial species were also cultured from upstream estuarine and riverine invertebrates. Exposure to human sewage sources, recent precipitation, and water temperature were significant risk factors for bacterial detection in sentinel mussel batches. These findings are consistent with the hypothesis that filter-feeding invertebrates along the coast concentrate fecal bacteria flowing from land to sea and show that the relationships between anthropogenic effects on coastal ecosystems and the environmental niches of fecal bacteria are complex and dynamic.     

Fishes and salinities in the St Lucia estuarine system—a review

The recorded salinity ranges of freshwater, estuarine and marine fish species in Lake St Lucia, a Ramsar and World Heritage Site, are documented. The freshwater group is most diverse and abundant under oligohaline conditions, although the Mozambique tilapia (Oreochromis mossambicus) was common under all salinity regimes. Estuary resident species also favoured oligohaline conditions but, in contrast to the freshwater taxa, were well represented in salinities up to 40 ‰. The marine group was most diverse and abundant within the salinity range 10–40 ‰, but a large number of species could also be found in salinities up to 70 ‰. Very few fish species were able to tolerate salinities between 70 ‰ and 110 ‰, with only O. mossambicus surviving for extended periods in salinities above 110 ‰. All the aquatic macrophytes and most of the zoobenthos within the lake appear to die out within the salinity range of 50–60 ‰, thus creating additional stress to those fish present under such conditions. The food resources least affected by extreme hypersalinity are the microphytobenthos and detritus food chains, with detritivorous fishes being dominant when the lake is in this state. Mass mortalities of fishes in Lake St Lucia have been recorded under both low (<5 ‰) and high salinity (>70 ‰) conditions. The fish kills are often triggered by exceptionally low or high water temperatures which affect the osmoregulatory abilities of these species. Hypersaline conditions and fish mortalities under the most recent closed estuary mouth conditions (2002–2005) are reviewed. If the surface area of St Lucia (35,000 ha) is compared to the total surface area of all South African estuaries (approximately 70,000 ha), then the possibility exists that the loss of the Lake St Lucia nursery area for estuary-associated marine fish species over the past few years may cause significant short-term declines in the future abundance of these taxa on both a local and regional scale.     

Enzymatic responses of the riceland prawn, <Emphasis Type="Italic">Macrobrachium lanchesteri</Emphasis>, to chlorpyrifos exposure

Cholinesterase (ChE) was characterized in whole bodies of adult riceland prawns, Macrobrachium lanchesteri, based on substrate preference and inhibitor sensitivity. M. lanchesteri ChE activity was mainly attributable to acetylcholinesterase (AChE) since it preferentially hydrolyzed an AChE-specific substrate, acetylthiocholine iodide, over s-butyrylthiocholine iodide and was sensitive to 1,5-bis-(4-allyldimethyl-ammoniumphenyl)-pentan-3-one dibromide, a specific inhibitor for AChE. The effect of chlorpyrifos exposure on M. lanchesteri were also investigated. The 24, 48, 72 and 96 h LC₅₀ values for chlorpyrifos were 3.37, 2.76, 2.58 and 2.53 μg L⁻¹, respectively. Based on these values, adult M. lanchesteri were exposed to 0.5, 1.5, 2.5 and 3.5 μg chlorpyrifos L⁻¹ for 24, 48, 72 and 96 h. Chlorpyrifos appeared to induce drastic enzymatic responses in M. lanchesteri. AChE activity was inhibited after 24 h of exposure in a dose- and time-dependent manner. The levels of lipid peroxidation increased significantly after 24 h of exposure. However, the activities of the antioxidant enzyme, catalase, and the detoxification enzyme, glutathione S-transferase, were reduced. In conclusion, M. lanchesteri is sensitive to chlorpyrifos and can serve as a bioindicator species for freshwater environmental assessment.     

Progress and opportunities in advancing near-term forecasting of freshwater quality

Near-term freshwater forecasts, defined as sub-daily to decadal future predictions of a freshwater variable with quantified uncertainty, are urgently needed to improve water quality management as freshwater ecosystems exhibit greater variability due to global change. Shifting baselines in freshwater ecosystems due to land use and climate change prevent managers from relying on historical averages for predicting future conditions, necessitating near-term forecasts to mitigate freshwater risks to human health and safety (e.g., flash floods, harmful algal blooms) and ecosystem services (e.g., water-related recreation and tourism). To assess the current state of freshwater forecasting and identify opportunities for future progress, we synthesized freshwater forecasting papers published in the past 5 years. We found that freshwater forecasting is currently dominated by near-term forecasts of water quantity and that near-term water quality forecasts are fewer in number and in the early stages of development (i.e., non-operational) despite their potential as important preemptive decision support tools. We contend that more freshwater quality forecasts are critically needed and that near-term water quality forecasting is poised to make substantial advances based on examples of recent progress in forecasting methodology, workflows, and end-user engagement. For example, current water quality forecasting systems can predict water temperature, dissolved oxygen, and algal bloom/toxin events 5 days ahead with reasonable accuracy. Continued progress in freshwater quality forecasting will be greatly accelerated by adapting tools and approaches from freshwater quantity forecasting (e.g., machine learning modeling methods). In addition, future development of effective operational freshwater quality forecasts will require substantive engagement of end users throughout the forecast process, funding, and training opportunities. Looking ahead, near-term forecasting provides a hopeful future for freshwater management in the face of increased variability and risk due to global change, and we encourage the freshwater scientific community to incorporate forecasting approaches in water quality research and management.     

Response of protozoans to detergent-enzymes

Summary These studies were divided into two parts: (1) time until death curves in which Paramecium caudatum Ehrenberg was exposed to selected concentrations of the detergent-enzyme Axion, and (2) exposure of fresh-water protozoan communities to selected concentrations of Axion. The former were carried out in test tubes, the latter in plastic troughs with a constantly flowing fluid. Both types of bioassays were carried out with filtered water from Douglas Lake, Michigan, U.S.A. at a temperature of about 25° C. One hundred percent of an exposed population of Paramecium caudatum was killed in 20 to 30 minutes at a concentration of 100 ppm of Axion. No appreciable change in the controls was noted during these tests. The bioassays with fresh-water protozoan communities were carried out in plastic troughs with a constant flow of Douglas Lake water. During the exposure period the lake water flow was stopped and a flow of Axion solution was substituted for approximately three hours. After this exposure period lake water flow were restored. The number of species was determined before and at intervals following exposure. Appropriate controls were maintained. A three hour exposure to 56 ppm (introduced concentration) of Axion caused a 35 percent reduction in the number of species in less than five hours with recovery to the original number in approximately 145 hours; a three hour exposure to 75 ppm caused a 54% reduction in number of species in less than five hours with recovery to the original number in approximately 240 hours; 100 ppm produced a 55 percent reduction with recovery in approximately 200 hours; 125 ppm produced a 48% reduction with recovery in approximately 148 hours; 200 ppm caused a 78% reduction with recovery in about 140 hours. Response patterns vary as do those of bioassays with single species. However, it is important to note that each test community had different types of species present, and it is quite likely that some communities had a higher percentage of sensitive species than others. Since this variation also occurs in nature the tests are probably representative of the differences that exist when natural communities are exposed to wastes. Variation in control troughs was less than ± 10 percent in the number of species.     

The sublethal effects of zinc at different water temperatures on selected haematological variables in Oreochromis mossambicus

Trace metals such as zinc play an important role in the normal metabolic functioning of all organisms. However, metals can become toxic if background concentrations are exceeded in the environment. This study investigated the sublethal effects of zinc on the haematology of Oreochromis mossambicus at different water temperatures. Fish were exposed to sublethal zinc (Zn) concentrations of 40μg/l (mean Zn concentration measured from the Mhlathuze River) for a period of 96h at different water temperatures representing the seasonal temperatures in the Mhlathuze River (18°C, 24°C, 28°C and 32°C). Exposure to zinc at 28°C and 32°C resulted in the most pronounced haematological changes in O. mossambicus. The erythrocytotic conditions found following exposure to Zn could be attributed to damage to the gill surface. The ensuing hypoxic conditions are alleviated through the release of large amounts of immature RBC into the circulatory system. The leucocytotic conditions support the findings of damage to the gill surface. The increased glucose concentrations were attributed to a general adaptation response whereby metabolites are mobilised to meet increased energy demands during periods of stress. The changes in Na⁺ and K⁺ levels in the plasma of O. mossambicus can be attributed to a combination of stimulation of Na-K ATPase activity, reduced membrane permeability in the gill tissue and leakage from cells into the blood, respectively.     

Impacts of Mercury on Freshwater Fish-Eating Wildlife and Humans

This paper reviews the current state of knowledge of the toxic effects of mercury on fish-eating birds, mammals, and humans associated with freshwater ecosystems, including new information on the relative risk of elevated methyl Hg exposure for fish-eating birds inhabiting aquatic ecosystems impacted by mining/smelting activities and areas characterized by high geological sources of Hg. The influence of various environmental conditions such as lake pH, DOC, and chemical speciation of Hg, on fish-Hg concentrations and Hg exposure in fish-eating wildlife, are discussed. Although a continuing global effort to decrease the release of this nonessential metal into the environment is warranted, Hg methylation and biomagnification may be limited in some environments due to chemical speciation of mercury in soils and sediments (e.g., HgS) and water quality conditions (e.g., high alkalinity and pH) that do not facilitate high methylation rates. We have shown such limitations for a lake where historic Hg mining greatly increased sediment-Hg loadings, yet Hg increases in small fish of various species are currently lower than expected, and top predators (bald eagles), despite having elevated concentrations of Hg in their blood compared with individuals from nearby lakes, exhibit no Hg-related reproductive impairment or other signs of MeHg intoxication. Recent epidemiological studies have shown that fish-eating human populations may be exposed to Hg sufficient to cause significant developmental effects. However, for humans, we conclude that the current USEPA reference dose for MeHg may be too restrictive, particularly for the less sensitive adult. The health status of indigenous peoples relying on the subsistence harvest of wild foods may be negatively affected by such restrictions.     

Chronic effects of low insecticide concentrations on freshwater caddisfly larvae

The insecticide load in surface waters does not ordinarily reach concentrations acutely toxic to aquatic fauna. The effects of the low insecticide concentrations typical of natural habitats are still not clear, for they often appear only after relatively long exposure times. To test such a situation, the insecticides lindane and parathion were introduced into a static-with-renewal outdoor aquaria system at concentrations about four and five orders of magnitude lower than their respective 96-h LC₅₀s, and their chronic (about 90 days) effects on the survival rate of freshwater caddisfly larvae were observed. The emergence and hence survival rate of Limnephilus lunatus Curtis was significantly reduced by lindane at 0.1 ng l^–1, a value nearly five orders of magnitude lower than the 96-h LC₅₀. Parathion, with acute and subacute toxicity similar to that of lindane, did not significantly alter the emergence rate of this species. In contrast, this substance did produce a significant reduction in emergence rate of the closely related species Limnephilus bipunctatus Curtis at 1 ng l^–1, even though this species was significantly less susceptible than L. lunatus to parathion at high concentrations. We conclude that chronic insecticide exposure can be hazardous to freshwater macroinvertebrates even at unexpectedly low concentrations. The low-concentration effects may depend on both species and substance and therefore cannot be predicted from toxicity data at higher concentrations.     

Comparison of leaf decomposition and macroinvertebrate colonization between exotic and native trees in a freshwater ecosystem

One of the most important sources of energy in aquatic ecosystems is the allochthonous input of detritus. Replacement of native tree species by exotic ones affects the quality of detritus entering freshwater ecosystems. This replacement can alter nutrient cycles and community structure in aquatic ecosystems. The aims of our study were (1) to compare leaf litter decomposition of two widely distributed exotic species (Ailanthus altissima and Robinia pseudoacacia) with the native species they coexist with (Ulmus minor and Fraxinus angustifolia), and (2) to compare macroinvertebrate colonization among litters of the invasive and native species. Litter bags of the four tree species were placed in the water and collected every 2, 25, 39, 71, and 95 days in a lentic ecosystem. Additionally, the macroinvertebrate community on litter bags was monitored after 25, 39, and 95 days. Several leaf chemistry traits were measured at the beginning (% lignin; lignin:N, C:N, LMA) and during the study (leaf total nitrogen). We detected variable rates of decomposition among species (k values of 0.009, 0.008, 0.008, and 0.005 for F. angustifolia, U. minor, A. altissima and R. pseudoacacia, respectively), but we did not detect an effect of litter source (from native/exotic). In spite of its low decay, the highest leaf nitrogen was found in R. pseudoacacia litter. Macroinvertebrate communities colonizing litter bags were similar across species. Most of them were collectors (i.e., they feed on fine particulate organic matter), suggesting that leaf material of either invasive or native trees was used as substrate both for the animals and for the organic matter they feed on. Our results suggest that the replacement of the native Fraxinus by Robinia would imply a reduction in the rate of leaf processing and also a slower release of leaf nitrogen to water.     

PARALYTIC SHELLFISH TOXINS ARE RESTRICTED TO FEW SPECIES AMONG AUSTRALIA'S TAXONOMIC DIVERSITY OF CULTURED MICROALGAE1

There are at least 40,000 species of microalgae in the aquatic environment. Fifteen species of marine dinoflagellates and freshwater cyanobacteria are known to produce paralytic shellfish toxins (PSTs) and represent a threat to human and/or livestock health. Although known toxic species are regularly monitored, the wider cross‐section of microalgae has not been systematically tested for PSTs. Advances in rapid screening techniques have resulted in the development of highly sensitive and specific methods to detect PSTs, including the sodium channel and saxiphilin binding assays. These assays were used in this study in 96‐well formats to screen 234 highly diverse isolates of Australian freshwater and marine microalgae for PSTs. The screening assays detected five toxic species, representing one freshwater cyanobacterium (Anabaena circinalis Rabenhorst) and four species of marine dinoflagellates (Alexandrium minutum Halim, A. catenella Balech, A. tamarense Balech, and Gymnodinium catenatum Graham). Liquid chromatography‐fluorescence detection was used to identify 14 saxitoxin analogues across the five species, and each species exhibited distinct toxin profiles. These results indicate that PST production is restricted to a narrow range of microalgal species found in Australian waters.