Effects of zinc and cadmium on oxygen consumption and ammonium excretion in pink shrimp (Farfantepenaeus paulensis, Pérez-Farfante, 1967, Crustacea)

Population-specific responses to pollution exposure suggest local adaptation of invasive red swamp crayfish Procambarus clarkii along the Mediterranean French coastline

Anthropogenic stressors can have an impact in a broad range of physiological processes and can be a major selective force leading to rapid evolution and local population adaptation. In this study, three populations of the invasive crayfish Procambarus clarkii were investigated. They are geographically separated for at least 20 years, and live in different abiotic environments: a freshwater inland lake (Salagou lake) with no major anthropogenic influence and two other coastal wetlands regularly polluted by pesticides along the Mediterranean coast (Camargue region and Bages-Sigean lagoon). Collected adults were genetically characterized using the mitochondrial COI gene and haplotype frequencies were analyzed for genetic variability within and between populations. Results revealed a higher genetic diversity for these invasive populations than any previous report in France, with more than seven different haplotypes in a single population. The contrasting genetic diversity between the Camargue and the other two populations suggest different times and sources of introduction. To identify differences in key physiological responses between these populations, individuals from each population were maintained in controlled conditions. Data on oxygen consumption rates indicate that the Salagou and Bages-Sigean populations possess a high inter-individual variability compared to the Camargue population. The low individual variability of oxygen consumption and low genetic diversity suggest a specific local adaptation for the Camargue population. Population-specific responses were identified when individuals were exposed to a pesticide cocktail containing azoxystrobin and oxadiazon at sublethal concentrations. The Salagou population was the only one with altered hydro-osmotic balance due to pollutant exposure and a change in protease activity in the hepatopancreas. These results revealed different phenotypic responses suggesting local adaptations at the population level.

Zinc is incorporated into the exoskeleton during post-ecdysial mineralization and inhibits exoskeletal calcification in the blue crab, Callinectes sapidus

Zinc is an essential but toxic metal with both natural and anthropogenic sources. Zinc has been reported to be present in crustacean exoskeleton, but it has remained unknown as to when zinc is incorporated into the shell during the molting cycle and the effects zinc has on exoskeleton properties. This study was conducted to identify a period during the molting cycle, in which zinc is incorporated into the exoskeleton of the blue crab, Callinectes sapidus, and to identify deleterious effects of zinc incorporation on the exoskeleton. It was hypothesized that zinc would be incorporated into the shell during the mineralization phase using calcium transporters, which would inhibit exoskeletal calcification. Post-ecdysial blue crabs were given two injections of zinc in the form of zinc chloride dissolved in Pantin's crustacean saline at the arthrodial membrane at three treatment levels: 0.0, 1.0 and 5.0 µg Zn/g wet weight. Exoskeletal and hemolymph samples were then analyzed for zinc, calcium, and magnesium content. Gill, muscle, and hepatopancreas samples were analyzed for zinc only. Epidermis samples were analyzed for carbonic anhydrase activity. The results showed that the injection dose of 1.0 µg Zn/g wet weight resulted in significant accumulation of zinc in the exoskeleton. There was no significant accumulation of exoskeletal zinc following 5.0 µg Zn/g wet weight injections. A significant reduction in exoskeletal calcium content in crabs treated with 1.0 or 5.0 µg Zn/g wet weight was also observed. The hypothetical model explaining zinc's incorporation into the exoskeleton and inhibition of exoskeletal calcification is proposed. Additionally, for the soft tissues examined, significant zinc accumulation was only observed in the hepatopancreas following zinc treatment. Our data points to the existence of crustacean zinc transporter. This study is the first to present evidence that zinc is deposited to the exoskeleton during post-ecdysial mineralization and inhibits exoskeletal calcification in a crustacean.

Methylmercury, Trace Metals, Organotins and Their Effects on the Qatari Mangrove Shrimp, Palaemon khori

The Qatari mangroves of Al-Khor are being increasingly exposed to a wide variety of anthropogenic pollutants due to land reclamation and urban expansion. In this study, we evaluated the lethal and genotoxic effects of methylmercury, trace metals, and organotins, assessing mortality and aneuploidy levels (abnormal number of chromosomes) in the endemic shrimp Palaemon khori under laboratory conditions. In the experimental design, two different concentrations were used for each family of contaminant (single or combined): an environmental concentration equivalent to the maximum value reported in the environment and a value ten times higher, for a period of eight weeks. Survival decreased significantly when pollutants were administrated in combination, even at environmental concentrations (as shown by Cox proportional hazards ratios): similar levels of mortality would be reached by individual type of pollutants only at ten times the environmental concentration. This critical result, under controlled lab conditions, highlights the importance of monitoring mixtures of contaminant types over single ones in the marine environment. Aneuploidy was reported in all treatments and control ranging from 5% to 19% at week four and from 7% to 21% at week eight. All treatments presented significantly higher aneuploidy levels when compared to the control. However, no significant difference was observed between the two time periods, even though 30% of the treatments could not be assessed at week eight, as not enough animals were still alive. In conclusion, the use of endemic species should be considered a valuable tool to determine local perturbations, representing a regional bioindicator of multiple environmental stressors from the initial stages of contamination.

Effects of cadmium on antioxidant and non-specific immunity of Macrobrachium nipponense

As a non-essential and toxic element, cadmium poses an important threat to aquatic organisms and human food safety. In this study, the effects of cadmium on antioxidant and non-specific immunity of Macrobrachium nipponense were studied from the physiological and biochemical indexes, histology and expression of related genes. These results showed that low concentrations (0.01, 0.02 mg/L) of cadmium have a positive effect on the non-specific immunity of M. nipponense, but high concentration (0.04 mg/L) of cadmium could inhibit or even damage the non-specific immunity of M. nipponense. The cadmium could induce oxidative stress in M. nipponense, and M. nipponense actived the antioxidant defense system to deal with oxidative stress, but high concentration (0.04 mg/L) of cadmium could inhibit the antioxidant defense system of M. nipponense, leading to oxidative damage, and may induce apoptosis in severe case. At the same time, the results of histology showed that cadmium can damage the structure of gill and hepatopancreas tissues of M. nipponense. This study provides theoretical data for evaluating the influences of heavy metal cadmium on M. nipponense and the toxic mechanism of heavy metal cadmium.

Comparative transcriptome analysis of the gills and hepatopancreas from Macrobrachium rosenbergii exposed to the heavy metal Cadmium (Cd2+)

Heavy metal Cadmium (Cd²⁺) pollution has become a severe environmental problem for aquatic organisms. In crustaceans, gills (Gi) and hepatopancreas (Hp) play a vital role in the toxicology. However, in Macrobrachium rosenbergill, there are few researches about gill and hepatopancreases responding to Cd²⁺ stress at a molecular level. In this study, transcriptomic analysis was applied to characterize gene expression profiles of gills and hepatopancreas of M. rosenbergill after Cd²⁺ exposure for 0 h, 3 h and 3 d. Six cDNA libraries (Gi 0 h, Gi 3 h, Gi 3 d, Hp 0 h, Hp 3 h, and Hp 3 d) were constructed and a total of 66,676 transcripts and 48,991 unigenes were annotated. Furthermore, differentially expressed genes (DEGs) were isolated by comparing the Cd²⁺ treated time-point libraries (3 h and 3 d group) with the control library (0 h group). The results showed that most of the DEGs were down-regulated after Cd²⁺ exposure and the number of DEGs among gill groups were significantly higher than those among hepatopancreas groups. GO functional and KEGG pathway analysis suggested many key DEGs in response to the Cd²⁺ stress, such as metallothionein and Hemocyanin. Additionally, a total of six DEGs were randomly selected to further identify their expressional profile by qPCR. The results indicated that these DEGs were involved in the response to Cd²⁺. This comparative transcriptome provides valuable molecular information on the mechanisms of responding to Cd²⁺ stress in M. rosenbergii, which lays the foundation for further understanding of heavy metal stress.

Low temperature stress in a cultured fish (Piaractus mesopotamicus) fed with Pyropia columbina red seaweed-supplemented diet

This study aimed to analyze the cold stress effects (in terms of hematology, energy reserves, and oxidative stress) in Piaractus mesopotamicus (pacú) and their mitigation by a Pyropia columbina red seaweed-supplemented diet. For this purpose, juvenile fish were fed with a control (CD) or a red seaweed-supplemented diet (RD) for 60 days, and then, the animals were exposed to a low temperature (14 °C) and a control temperature (24 °C) for 24 h. The cold shock generated an increase of hemoglobin levels in fish fed with both diets. In CD-fed fish, plasmatic triglycerides, cholesterol, and hepatic glycogen decreased after the thermal shock; meanwhile, the animals fed with RD showed decreased hepatic proteins, but increased cholesterol and hepatic glycogen. Regarding oxidative stress, antioxidant enzymes augmented their activity in the liver, intestine, and gills; meanwhile, lipid oxidative damage was observed in the liver and intestine of fish exposed to 14 °C and fed with both diets. Pacú was sensitive to cold shock, but no mitigation effects were observed in fish fed with the supplemented diet. Further research should target higher concentrations of P. columbina in supplemented diets to take advantage of this valuable resource.

Chemical Contents of Disposed Light Sticks Affect the Physiology of Rocky Crab Pachygrapsus transversus and Gray Shrimps Litopennaeus vanammei

Light-sticks shine resulting from a chemiluminescent reaction between two components kept separate by a glass ampoule. Light-stick baits are discarded in the ocean after being used in longline fishing. The traditional Brazilian community of Costa dos Coqueiros, Brazil, uses the discarded light-sticks chemical contents found on beaches as medicine for rheumatism and mycoses. This study assessed the effects that light-sticks (chemical contents) have on Pachygrapsus transversus and Litopennaeus vanammei. Assays of metabolic changes involved rates of ammonia excretion and oxygen consumption. The EC50-60 min to juveniles and adults P. transversus were 0.0004% and 0.0046%, respectively; and L. vanammei revealed a susceptible species: EC50-60 min of 0.0006% for oxygen uptake and 0.0072% for ammonia excretion, and also was observed a hormesis effect in the ammonia excretion. Light-stick contents could promote significant metabolic changes in rocky crabs and gray shrimp. Educational actions are needed that make the population aware of and avoid the dangerous misuse of the light-sticks.

Lethal and long-term effects of landfill leachate on Eisenia andrei earthworms: Behavior, reproduction and risk assessment

Leachate is difficult to biodegrade, and presents variable physical, chemical and biological characteristics, as well as high toxicological potential for soil, groundwater and water bodies. In this context, untreated leachate toxicity was evaluated through acute and chronic exposures in Eisenia andrei earthworms. Physico-chemical leachate characterizations indicate a complex composition, with high organic matter (COD - 10,634 mg L^-1) and ammoniacal nitrogen (2388 mg L^-1) concentrations. Metals with carcinogenic potential, such as Cr, As and Pb, were present at 0.60, 0.14 and 0.01 μg L^-1, respectively and endocrine disrupting compounds were detected in estradiol equivalents of 660 ± 50 ng L^-1. Acute tests with Eisenia andrei indicated an LC₅₀ (72 h) of 1.3 ± 0.1 μL cm^-2 in a filter paper contact test and 53.9 ± 1.3 mL kg^-1 in natural soil (14 days). The EC₅₀ in a behavioral test was estimated as 31.6 ± 6.8 mL kg^-1, indicating an escape effect for concentrations ranging from 35.0 to 70.0 mL kg^-1 and habitat loss from 87.5 mL kg^-1 of leachate exposure. Chronic exposure (56 days) led to reproduction effects, resulting in a 4-fold decreased cocoon production and 7-fold juvenile decrease. This effect was mainly attributed to the possible presence of endocrine disrupting compounds. An estimated NOAEL of 1.7 mL L^-1 and LOAEL of 3.5 mL L^-1 were estimated for earthworms exposed to the assessed effluent. Extremely high-risk quotients (RQ ≥ 1) were estimated based on leachate application in irrigation. Thus, adequate municipal solid waste management is paramount, especially with regard to generated by-products, which can result in high toxicological risks for terrestrial organisms.

Why Protect Decapod Crustaceans Used as Models in Biomedical Research and in Ecotoxicology? Ethical and Legislative Considerations

Simple Summary

Current European legislation that protects animals used for scientific purposes excludes decapod crustaceans (for example, lobster, crab and crayfish) on the grounds that they are non-sentient and, therefore, incapable of suffering. However, recent work suggests that this view requires substantial revision. Our current understanding of the nervous systems and behavior of decapods suggests an urgent need to amend and update all relevant legislation. This paper examines recent experiments that suggest sentience and how that work has changed current opinion. It reflects on the use of decapods as models in biomedical research and in ecotoxicology, and it recommends that these animals should be included in the European protection legislation.

Abstract

Decapod crustaceans are widely used as experimental models, due to their biology, their sensitivity to pollutants and/or their convenience of collection and use. Decapods have been viewed as being non-sentient, and are not covered by current legislation from the European Parliament. However, recent studies suggest it is likely that they experience pain and may have the capacity to suffer. Accordingly, there is ethical concern regarding their continued use in research in the absence of protective measures. We argue that their welfare should be taken into account and included in ethical review processes that include the assessment of welfare and the minimization or alleviation of potential pain. We review the current use of these animals in research and the recent experiments that suggest sentience in this group. We also review recent changes in the views of scientists, veterinary scientists and animal charity groups, and their conclusion that these animals are likely to be sentient, and that changes in legislation are needed to protect them. A precautionary approach should be adopted to safeguard these animals from possible pain and suffering. Finally, we recommend that decapods be included in the European legislation concerning the welfare of animals used in experimentation.

Acute and sub-chronic effects of copper on survival, respiratory metabolism, and metal accumulation in Cambaroides dauricus

Trace metal contamination in the aquatic ecosystem occurs worldwide: although copper is an essential trace metal, it is considered as a pollutant at certain levels in China. Freshwater crayfish Cambaroides dauricus is a commercially important wild species in northeastern China, in which is an important heavy industry area. The population of C. dauricus was decreasing sharply due to the environmental pollution and human intervention over the past 20 years. However, nothing is known regarding the responses of this species to trace metal toxicants. This study aimed to determine the acute and chronic toxicity of Cu and its toxicological effects on respiratory metabolism, as well as Cu accumulation in C. dauricus. The acute (96 h) median lethal concentration (LC50) value of 32.5 mg/L was detected in C. dauricus. Then, acute (96 h; 8.24, 16.48 mg/L) and sub-chronic (14 days; 2.06, 4.12 mg/L) exposure in Cu was investigated by estimating the oxygen consumption rate, ammonium excretion rate, and Cu accumulation. Both acute and sub-chronic Cu exposure induced an inhibition of the oxygen consumption rate and ammonium excretion rate, and thereby, an increased O:N ratio. The shift in O:N ratio indicated a metabolic substrate shift towards lipid and carbohydrate metabolism under Cu stress. Cu accumulation in the hepatopancreas and muscles throughout the study was found to be time-dependent and concentration-dependent. The maximum accumulation in the hepatopancreas and muscle were almost 31.6 folds of the control after 14 days' exposure to 4.12 mg/L concentration. Based on the present work, we suggest that crayfish be considered a potential bioindicator of environmental pollution in freshwater systems. The study provides basic information for further understanding of the toxicological responses of this species to trace metals.

Respiratory Metabolism and Antioxidant Response in Chinese Mitten Crab Eriocheir sinensis During Air Exposure and Subsequent Reimmersion

Chinese mitten crab, Eriocheir sinensis, often suffers from severe air exposure stress during transportation and culture; high mortality occurs due to desiccation. In this study, the effects of air exposure stress (0, 2, 4, 8, and 16 h) and reimmersion (2, 6, 12 h) on respiratory metabolism and antioxidant responses in Chinese mitten crabs were studied under laboratory conditions. The results showed that air exposure and reimmersion had a significant impact on the oxygen consumption rate (OCR), ammonia excretion rate (AER), oxygen to nitrogen ratio (O:N), superoxide dismutase (SOD), catalase (CAT), succinate dehydrogenase (SDH), and lactate dehydrogenase (LDH). Significant interaction between air exposure and reimmersion was observed for OCR, AER, O:N, SOD, CAT, SDH, and LDH in Chinese mitten crab. During the air exposure stage, SOD, CAT, and LDH activities in the gills and hepatopancreas first increased and then decreased as air exposure time increased. All of these parameters were significantly higher in the 4-h air exposure group than those in the control group. All the parameters were significantly lower in the 16-h air exposure group than those in the control group, except LDH in the hepatopancreas. However, SDH activity gradually decreased with increased air exposure time, and all the air exposure groups were markedly lower than those in the control group in the gills. During the reimmersion stage, OCR, AER, and O:N restored to normal levels after 12-h reimmersion, except in the 16-h air exposure group, where OCR and O:N were significantly higher than those in the control group and AER was significantly lower than that in the control group. The LDH activity in all groups restored to normal levels after 12-h reimmersion. The SDH, SOD, and CAT activities of the 2- and 4-h air-exposed groups returned to normal levels after 12-h reimmersion; however, these three parameters were still significantly higher in the 16-h air-exposed group than in the control group in the gills and hepatopancreas. Overall, Chinese mitten crabs reduce aerobic respiration and increase anaerobic respiration capacity during desiccation. Under air exposure stress, Chinese mitten crabs change their energy utilization mode to meet their energy demands and adjust their respiratory metabolism and antioxidant enzymes activities to adapt to adverse environments.

Effects of water-borne copper and lead on metabolic and excretion rate of bahaii loach (Turcinoemacheilus bahaii)

Beyond the role of anthropogenic activities, natural sources of metal contaminations are still controversial, together counting, however, as a major threat to inland and coastal waters, becoming an even more prominent stressor for aquatic life. To address the effects of metals on the physiological response of fish, standard metabolic rate (SMR), maximum metabolic rate (MMR), aerobic scope (AS) and factorial aerobic scope (FAS) as well as specific rate of ammonia excretion (J_amm) of Turcinoemacheilus bahaii were determined following different water-borne Cu²⁺ and Pb²⁺ treatments. Following LC₅₀-96 h determination, 72 fish (BW = 1.153 ± 0.56 g and TL = 6.155 ± 0.97 cm) were exposed to different amounts of Cu²⁺ and Pb²⁺ in 9 different treatments (eight fish/treatment), including 0.910 mg l^-1 Cu²⁺ for 24 h, 0.455 mg l^-1 Cu²⁺ for 7d, 0.182 mg l^-1 Cu²⁺ for 14d and 0.091 mg l^-1 Cu²⁺ for 30 d as well as 124.430 mg l^-1 Pb²⁺ for 24 h, 62.215 mg l^-1 Pb²⁺ for 7d,12.443 mg l^-1 Pb²⁺ for 14d, 6.221 mg l^-1 Pb²⁺ for 30d and control. The SMR of fish was reduced following exposures to all Cu²⁺ and Pb²⁺ treatments (P < 0.05), except for 30d exposure as compared with the control. The MMR remained steady following all Cu²⁺ treatments while it was raised significantly (P < 0.05) following Pb²⁺ treatments at 7, 14 and 30d exposure. Although the AS showed a similar pattern to MMR, the FAS was elevated (P < 0.05) following all the treatments when compared with control. Lower J_amm were observed following all metals-treated fish in comparison with control (P < 0.05). In addition, higher (P < 0.05) levels of injuries were observed following all Cu²⁺ and Pb²⁺ treatments in gills and kidneys. The results suggest that Cu²⁺ and Pb²⁺ over the experimental period could impair the metabolic and excretory capacities, hence affecting the possible physiological performance of fish.

Metabolic and oxidative stress responses of the jellyfish Cassiopea to pollution in the Gulf of Aqaba, Jordan

Physiological responses of jellyfish to pollution are virtually overlooked. We measured the activity of two glycolytic enzymes (pyruvate kinase (PK) and lactate dehydrogenase (LDH)), lipid peroxidation (LPO), protein and chlorophyll a content in the jellyfish Cassiopea sp. from polluted and reference sites along the Gulf of Aqaba, Jordan. In jellyfish from polluted sites, low PK/LDH ratios and high LDH activity clarify their reliance on anaerobic metabolism. PK and LDH were positively correlated in the jellyfish. While medusae from polluted sites showed no signs of oxidative stress damage, protein content was significantly lower. This might suggest protein utilization for energy production needed for maintenance. Unchanged LPO in polluted sites indicates the ability of jellyfish to keep reactive oxygen species under control. Overall these results suggest that the jellyfish seems to tolerate the current levels of pollution at the studied sites and they might be anaerobically poised to live at such habitats.

Acute toxic effects of zinc and mercury on survival, standard metabolism, and metal accumulation in juvenile ridgetail white prawn, Exopalaemon carinicauda

Ridgetail white prawn (Exopalaemon carinicauda) is widely distributed in Chinese coastal zones, especially in the Yellow Sea and Bohai Sea. It is not only considered as an important economic species in China, but also taken as a potential indicator species for the environmental pollution in the estuaries. At present, the responses of this species to environmental toxicants, including trace metal are not well understood. In this study, the acute toxic effects of zinc (Zn) and mercury (Hg) on the survival, oxygen consumption, ammonia-N excretion, and metal accumulation were investigated in the juveniles of E. carinicauda. The median lethal concentrations (LC₅₀) of Zn were 76.4, 44.0, 30.2, and 17.2mg/L, respectively, after the juveniles were exposed in for 24, 48, 72, and 96h, and the LC₅₀ of H_g was 0.212, 0.096, 0.084, and 0.065mg/L under the same exposure duration. The juveniles decreased the oxygen consumption by 51.4%, and increased ammonia-N excretion by 129% when they were exposed in Zn at the concentration of 76.4mg/L compared with their controls without Zn exposure, therefore the O:N ratio decreased by 82.9% compared with the control. Hg exposure with the concentration of 0.212mg/L caused the inhibition of oxygen consumption by 48.1% and increasement of ammonia-N excretion by 161%, and the atomic ratio of consumed oxygen to excreted ammonia-nitrogen (O:N ratio) decreased by 80.6% in the juveniles in comparison with the control. A concentration-dependent accumulation of heavy metals was observed in the gills, hepatopancreas and muscles of the experimental animals, with a maximum accumulation of 16.3 folds for Zn and 72.8 fold for Hg in the gills of the juveniles after 24h exposure. The data obtained from the present study would provide useful information for help further understanding on the toxicological responses of this species to trace metals.

The Effects of Temperature and Hydrostatic Pressure on Metal Toxicity: Insights into Toxicity in the Deep Sea

Mineral prospecting in the deep sea is increasing, promoting concern regarding potential ecotoxicological impacts on deep-sea fauna. Technological difficulties in assessing toxicity in deep-sea species has promoted interest in developing shallow-water ecotoxicological proxy species. However, it is unclear how the low temperature and high hydrostatic pressure prevalent in the deep sea affect toxicity, and whether adaptation to deep-sea environmental conditions moderates any effects of these factors. To address these uncertainties we assessed the effects of temperature and hydrostatic pressure on lethal and sublethal (respiration rate, antioxidant enzyme activity) toxicity in acute (96 h) copper and cadmium exposures, using the shallow-water ecophysiological model organism Palaemon varians. Low temperature reduced toxicity in both metals, but reduced cadmium toxicity significantly more. In contrast, elevated hydrostatic pressure increased copper toxicity, but did not affect cadmium toxicity. The synergistic interaction between copper and cadmium was not affected by low temperature, but high hydrostatic pressure significantly enhanced the synergism. Differential environmental effects on toxicity suggest different mechanisms of action for copper and cadmium, and highlight that mechanistic understanding of toxicity is fundamental to predicting environmental effects on toxicity. Although results infer that sensitivity to toxicants differs across biogeographic ranges, shallow-water species may be suitable ecotoxicological proxies for deep-sea species, dependent on adaptation to habitats with similar environmental variability.

Effects of waterborne cadmium on energy metabolism in the tropical sea cucumber, Stichopus horrens, and a comparison of tissue-specific cadmium accumulation with the temperate sea cucumber Australostichopus mollis

The sea cucumber Stichopus horrens is an important component of near-shore ecosystems, and in the Kingdom of Tonga it also comprises an important commercial and subsistence fishery. To assess the sensitivity of this species to the toxic trace metal cadmium (Cd), adult S. horrens were exposed for 96h to an environmental (15µgL^-1) or effect (765µgL^-1) concentration of waterborne Cd. The respiratory tree and intestine accumulated higher concentrations of Cd than the muscle and body wall, but there were no effects of Cd on tissue ions (sodium, potassium, magnesium, calcium). For comparison, Cd accumulation was also examined in the Australasian sea cucumber Australostichopus mollis. This species displayed a similar pattern of tissue-specific accumulation to S. horrens, but exhibited lower tissue Cd burdens, likely a consequence of lower experimental temperature. Effects on gonad ion content were also seen in this species. At the highest Cd exposure concentration, S. horrens showed impaired ammonia excretion rates and an increased molar oxygen:nitrogen ratio (O:N), indicative of a decreased reliance on protein metabolism. Overall, this study suggests that S. horrens is relatively tolerant of Cd exposure, but raises concerns regarding the subsistence fishery practice of consuming the viscera of this species.

Acute and sub-chronic effects of sub-lethal cadmium exposure on energy metabolism in the freshwater shrimp, Paratya curvirostris

Cadmium (Cd) is a toxic trace element enriched in waters through activities such as mining and agriculture. The freshwater shrimp Paratya curvirostris inhabits near-coastal, lowland streams potentially impacted by Cd, but nothing is known regarding its sensitivity to this metal. An acute (96h) median lethal concentration (LC₅₀) of 405µgL^-1 was derived for P. curvirostris, placing it among the most tolerant of freshwater shrimp species. Acute (4 d; 0, 50 and 100µgL^-1) and sub-chronic (10 d; 0, 25 and 50µgL^-1) exposures then investigated effects of Cd on energy metabolism (respiration rate, excretion rate, O:N ratio). In contrast to effects in previously studied species, Cd induced an increased respiration rate, which when coupled with an unchanged excretion rate, resulted in an increased O:N ratio. These data were explained by an increased reliance on carbohydrate and/or lipid as a metabolic substrate stimulated by increased metabolic costs of toxicant exposure. Similar effects were seen across all time-points, although the lowest effective Cd concentration decreased with increased exposure time. Overall, results suggest that Cd is unlikely to be a significant environmental stressor to P. curvirostris, except in highly contaminated freshwaters, and/or where Cd co-occurs with hypoxia.

Bioaccumulation, morphological changes, and induction of metallothionein gene expression in the digestive system of the freshwater crab Sinopotamon henanense after exposure to cadmium

To study the responses of digestive system of the freshwater crab Sinopotamon henanense to the exposure with cadmium (Cd), crabs were acutely exposed to 7.25, 14.50, and 29.00 mg/l Cd for 96 h and subchronically exposed to 0.725, 1.450, and 2.900 mg/l for 21 days. Cd bioaccumulation in the hepatopancreas and digestive tract (esophagus and intestine) was examined. Furthermore, histopathological alterations of the esophagus, midgut, hindgut, and hepatopancreas were assessed in animals from the 29.0 and 2.90 mg/l Cd treatment groups, and expression of metallothionein messenger RNA (MT mRNA) in the hepatopancreas and intestine was measured in all treatment groups. The results showed difference in the middle and high concentrations between acute and subchronic treatment groups. Cd content in digestive tract after acute 14.5 and 29.0 mg/l Cd exposure was significantly higher than that at subchronic 1.45 and 2.90 mg/l exposure, but Cd levels in hepatopancreas were not significantly different under the same condition. Acute exposure to Cd induced greater morphological damage than subchronic exposure: large areas of epithelial cells were necrotic in hepatopancreas and midgut, which detached from the basal lamina. Vacuolated muscle cells were observed in the hindgut of animals from the acute exposure group, but the changes of esophageal morphology were not obvious after acute or subchronic treatments. The expression of MT mRNA increased with increasing Cd concentration, and MT mRNA level in acute exposure groups was significantly lower when compared to the subchronic exposure groups. Higher Cd content and lower MT mRNA expression in the acutely exposed groups may be responsible for more severe damage of digestive system in these exposure groups.

Trace elements distribution in hawksbill turtle (Eretmochelys imbricata) and green turtle (Chelonia mydas) tissues on the northern coast of Bahia, Brazil

Concentrations of elements (As, Al, Ba, Ca, Cd, Co, Cr, Cu, Fe, Hg, K, Mg, Mn, Mo, Na, Ni, Pb, Sb, Se, Sr, V, Zn) were determined in liver, kidneys and bones of Eretmochelys imbricata and Chelonia mydas specimens found stranded along the northern coast of Bahia, Brazil. Results showed that the concentrations of Cd, Cu, Ni and Zn in the liver and kidneys of juvenile C. mydas were the highest found in Brazil. We also observed a significant difference (p<0.05) on the bioaccumulation of trace elements between the two species: Al, Co, Mo, Na and Se in the liver; Al, Cr, Cu, K, Mo, Ni, Pb, Sr and V in the kidneys; and Al, Ba, Ca, Cd, Mn, Ni, Pb, Se, Sr and V in the bones. This study represents the first report on the distribution and concentration of trace elements in E. imbricata in the Brazilian coast.

Carotenoid as a sensitive indicator of sub lethal cadmium toxicity in Penaeus monodon post larvae

The objective of the present study is to evaluate a sensitive indicator of cadmium by measuring oxygen consumption and carotenoid concentration in post larvae of Penaeus monodon. The post larvae of P. monodon were exposed to 0.12 and 0.24 mg/L of cadmium in the laboratory for a period of 30 days. These concentrations represent 1/10th and 1/5th of 96 h LC50 value for the post larvae. Oxygen consumption and carotenoid concentration were measured at 24, 48, 96 h, 10 and 30 days of cadmium exposure. The results indicated an inhibition of routine oxygen consumption in post larvae at different intervals of exposure from 24 h to 30 days but the effect was statistically significant (P < 05) at 30 days of exposure at both sub lethal concentrations, where the inhibition was 38.5 % at 0.24 mg/L and 21.6 % at 0.12 mg/L. On the other hand, carotenoid concentrations increased gradually with increasing period of exposure as well as concentration, and this increase was statistically significant (P < 0.05) from 96 h onwards on exposure to 0.12 mg/L and from 48 h onwards on exposure to 0.24 mg/L of cadmium, with an overall highest increase of 135 %. As carotenoid content is an indicator of tissue oxygen, inhibition of routine oxygen consumption might have resulted in enhancing the levels of carotenoid. From the present data, it is evident that carotenoid concentration can be considered as a sensitive indicator of cadmium toxicity than routine oxygen consumption in the post larvae of P. monodon. The present investigation is also relevant for environmental monitoring of cadmium in coastal waters before it is used for aquaculture.

Acute effects of cadmium and copper on survival, oxygen consumption, ammonia-N excretion, and metal accumulation in juvenile Exopalaemon carinicauda

Ridgetail white prawn (Exopalaemon carinicauda), a commercially important species in China, is a potential candidate for evaluating impairments caused by environmental pollutants in coastal and estuarine areas. The main purpose of the present study was to investigate the acute effects of cadmium (Cd) and copper (Cu) on survival, oxygen consumption, ammonia-N excretion, and metal accumulation in E. carinicauda. The feasibility of using this species for pollution monitoring was also evaluated. Results showed that the median lethal concentrations (LC50) for 24h, 48h, 72h, and 96h were 0.66mg/L, 0.379mg/L, 0.343mg/L, and 0.258mg/L for Cd, and 0.932mg/L, 0.748mg/L, 0.725mg/L, and 0.712mg/L for Cu. Cd exposure (0.66mg/L) caused an inhibition in oxygen consumption of 21.1 percent and an increase in ammonia-N excretion of 47.1 percent, thereby decreasing the atomic ratio of oxygen consumed to nitrogen consumed (O:N ratio) of 46.32 percent relative to the control. Cu exposure (0.932mg/L) also resulted in an inhibition in oxygen consumption of 34.8 percent and a decrease in the O:N ratio of 23.9 percent in relation to the control, but the ammonia-N excretion was not influenced by the Cu exposure. Concentration-depended accumulation was observed in the experimental animals, which a maximum of 244.8 folds and 1.1 folds increase of mental concentration was measured upon exposure to 24h LC50 of Cd and Cu for 24h, respectively. The change in O:N ratio indicated an alteration in energy utilization. Based on its sensitivity to heavy metals and its availability all year round, E. carinicauda can be used as a test organism to monitor for metal pollution.

Development of a promising fish model (Oryzias melastigma) for assessing multiple responses to stresses in the marine environment

With the increasing number of contaminants in the marine environment, various experimental organisms have been “taken into labs” by investigators to find the most suitable environmentally relevant models for toxicity testing. The marine medaka, Oryzias melastigma, has a number of advantages that make it a prime candidate for these tests. Recently, many studies have been conducted on marine medaka, especially in terms of their physiological, biochemical, and molecular responses after exposure to contaminants and other environmental stressors. This review provides a literature survey highlighting the steady increase of ecotoxicological research on marine medaka, summarizes the advantages of using O. melastigma as a tool for toxicological research, and promotes the utilization of this organism in future studies.

Potential adverse effects of inorganic pollutants on clinical parameters of loggerhead sea turtles (Caretta caretta): results from a nesting colony from Cape Verde, West Africa

A large number of nesting loggerhead sea turtles (n = 201) were sampled to establish the blood levels of 11 elements (Cu, Mn, Pb, Zn, Cd, Ni, Cr, As, Al, Hg, and Se). Almost all of the samples showed detectable levels of these 11 elements, and Zn and Se exhibited the highest concentrations (median values as high as 6.05 and 2.28 μg/g, respectively). The median concentrations of the most toxic compounds, As, Cd, Pb, and Hg, were relatively low (0.38, 0.24, 0.06, and 0.03 μg/g, respectively). We also determined the haematological and biochemical parameters in a subsample of 50 turtles to evaluate the potential effects of these contaminants on clinical parameters and found several associations. Our study reinforces the usefulness of blood for the monitoring of the levels of contaminating elements and their adverse effects on blood parameters in sea turtles.

Assessment of acute toxicity of carbofuran in Macrobrachium olfersii (Wiegmann, 1836) at different temperature levels

Carbofuran (2,3-dihydro-2,2-dimethyl-7-benzofuranyl methylcarbamate; C12H15NO3) is one of the most toxic carbamate pesticides. For acute toxicity of carbofuran, juveniles of Macrobrachium olfersii were exposed to different concentrations of carbofuran using the static renewal method at different temperature levels (15, 20 and 25°C) at pH 7.0. The main purpose of the present study was to detect the acute toxicity of carbofuran to M. olfersii and investigate its effects on oxygen consumption and ammonium excretion; these tests have not been carried out in this species before. First, the acute toxicity – median lethal concentration – of carbofuran to M. olfersii for 24, 48, 72 and 96 h was examined, which resulted in the following values: 1.64, 1.22, 0.86 and 0.42 mg L−1, respectively. Furthermore, we also found that carbofuran caused an inhibition in oxygen consumption of 60.6, 65.3 and 66.2% with respect to the control. In addition, after separate exposures to carbofuran, elevations in ammonium excretion were more than 500% with respect to the control.

The use of oxygen consumption and ammonium excretion to evaluate the toxicity of cadmium on Farfantepenaeus paulensis with respect to salinity

The main purpose of the present study was to detect the acute toxicity of cadmium (Cd) in F. paulensis and to investigate its effect on oxygen consumption and ammonium excretion different salinities. First, we examined the acute toxicity of Cd in F. paulensis at 24, 48, 72, and 96-h lethal concentration (LC50). Cd was significantly more toxic at 5 salinity than at 20 and 36. The oxygen consumption and ammonium excretion were estimated through experiments performed on each of the twelve possible combinations of three salinities (36, 20 and 5), at temperature 20°C. Cd showed a reduction in oxygen consumption at 5 salinity, the results show that the oxygen consumption decreases with respect to the Cd concentration. At the highest Cd concentration employed (2 mg L(-1)), the salinity 5 and the temperature at 20°C, oxygen consumption decreases 53.7% in relation to the control. In addition, after separate exposure to Cd, elevation in ammonium excretion was obtained, wish were 72%, 65% and 95% higher than the control, respectively. The results show that Cd is more toxic to F. paulensis at lower salinities.

Toxicity of metal mixtures to the Pacific white shrimp Litopenaeus vannamei postlarvae

According to the literature, the safe level of a toxic substance for any given organism may be calculated from its median lethal concentration multiplied by a suitable application factor (AF: usually 0.1 and 0.01). The medial lethal concentrations for Litopenaeus vannamei postlarvae exposed to the mixtures in equitoxic proportions of Cd-Hg, Hg-Zn and Hg-Pb were close to one order of magnitude lower than the values calculated from individual toxicity tests, indicating a synergistic effect, while the mixture Cd-Zn showed an antagonistic effect. Exposure to the mixture of Cu, Fe, Mn, Zn, Cd, Hg and Pb caused 63.3% and 100% mortality after 21 and 13 days for 0.05 and 0.1 AF, showing that environmental safe concentrations of toxicants should not be calculated from individual toxicity tests.