First baseline for bioenergetic biomarkers in Cnesterodon decemmaculatus as test organism in ecotoxicological studies.

Cnesterodon decemmaculatus is a Neotropical teleost fish frequently used in ecotoxicological evaluations, whose biology has been thoroughly studied. Although there is considerable information on its response to different toxicants, no range of reference values has been so far established for the different biological parameters proposed as biomarkers of effect or exposure. Moreover, no study has yet examined the possible influence of the metabolic status of the exposed animals on their response to toxic stress. Therefore, the aim of this work was to provide a first baseline for a set of bioenergetic biomarkers in C. decemmaculatus adults exposed to a control medium under previously standardized conditions, and to assess their possible intrinsic seasonal variability. The responses of the biomarkers obtained from the controls were contrasted with those from the reference toxicant (Cadmio-Cd) and receiving waters (surface waters of the Reconquista River RR, Buenos Aires Province, Argentina). We conducted four 12-day assays (one in each season) of exposure to control media, (reconstituted moderate hard water, MHW) and two assays of exposure to Cd in MHW and surface river water (RR) in both summer and autumn. The variables recorded were: Food intake (In), fecal production (F), specific assimilation (A) and cumulative mortality, oxygen extraction efficiency (OEE), specific metabolic rate (SMR), ammonia excretion (N), ammonia quotient (AQ) and scope for growth (SFG). The seasonal variation shown by some physiological parameters, points to the need for establishing a baseline obtained from standardized media, preferably on a seasonal basis. Moreover, SFG and A appeared as the most sensitive biomarkers, emphasizing the importance to consider the metabolic status of the test organisms for the appropriate interpretation of results from ecotoxicological studies performed under controlled experimental conditions. The obtained results provide useful information on C. decemmaculatus as model species in ecotoxicological bioassays involving biomarkers of early effect.

Cadmium effects on some energy metabolism variables in Cnesterodon decemmaculatus adults.

This work is focused on the responses of some energy metabolism variables in Cnesterodon decemmaculatus adults exposed to cadmium under controlled laboratory conditions. This species has been used as bioindicator for evaluating the effects of different chemicals on diverse biological processes and is frequently used as test organism in ecotoxicity studies that include cadmium as reference toxicant. Animals were exposed for 12 days to the following concentrations: 0, 0.45, and 0.8 mg Cd/L. Food intake, fecal production, specific assimilation, condition factor, mortality percentage, oxygen consumption, oxygen extraction efficiency, specific metabolic rate, ammonia excretion, and ammonia quotient were measured. The overall balance was expressed as scope for growth (SFG). Cadmium-exposed groups showed a significant decrease in food assimilation and condition factor at the end of the exposure. There was an increase in specific metabolic rate and a decrease in SFG in the group exposed to 0.8 mg Cd/L. The condition factor and the SFG appeared as sensitive biomarkers of health status and growth of the animals, respectively. Cadmium-exposed fish reduced food intake, which was reflected in a decreased assimilation with concomitant decline in the external energy supply from feeding. Our results highlight the importance of considering the metabolic status of the test organisms when analyzing the responses of the biomarkers usually used as effect parameters in ecotoxicological evaluations under experimental conditions.

Infectivity of Chordodes nobilii larvae (Gordiida: Nematomorpha).

The gordiids are freshwater representatives of the parasite phylum Nematomorpha that function as a link between aquatic and terrestrial ecosystems. In recent years, different ecotoxicologic studies have been made with the South-American gordiid species, Chordodes nobilii, that have demonstrated the capacity of this group to act as a bioindicator of contamination. Despite the Gordiida's ecologic relevance, further studies are still needed to elucidate different aspects of the biology of the class, and among those, the infective capacity, a parameter that can be evaluated by the infection index mean abundance (IIMA). A knowledge of the intrinsic variability in the infective capacity of C. nobilii would warrant priority in order to establish, the range of acceptable responses for normal or standard conditions in the laboratory, and, to compare the criteria among different assays. The objective of this study was to establish a baseline value for the infective capacity for C. nobilii larvae, under controlled laboratory conditions, by employing the IIMA as the evaluation parameter. To that end, we analyzed the infective capacity of C. nobilii larvae that had hatched from different strings of eggs laid in the laboratory by a total of 12 females. The C. nobilii adults were collected from streams within the Argentina Sauce Grande basin, between 2006 and 2009. Once in the laboratory, after mating, the females were placed in individual containers for oviposition. The egg strings obtained from each female were cut in 3 mm long segments; and when free larvae were observed, the segments (N= 90) were placed together with 30 Aedes aegypti larvae for evaluation of the gordiids' infective capacity. After 72 h, the mosquito larvae were observed by microscopy in order to quantify the C. nobilii larvae in body cavities. The IIMAs were calculated as the total number of C. nobilii larvae present divided by total number of A. aegypti larvae examined. For analysis of the IIMAs obtained, the data were grouped according to the female who made the original ovoposition. Our results enabled the corroboration of an ample range of responses in the infective capacity of this species, a characteristic that would normally be linked to the progenitors originating the hatch. Because this relationship prevents the establishment of a baseline for making comparisons among assays with gordiids, through the IIMA as a response parameter, we recommend expressing the IIMA values in each assay relative to their respective controls. These findings also provide evidence for the greater success in infections by certain members of the progeny over others. Finally, on the basis of the results obtained from this study, we stress the relevance of the use of the IIMA as a decisive aspect to be considered in different studies on the biology of Gordiida.

Biochemical responses of ecological importance in males of the austral South America amphipod Hyalella curvispina Shoemaker, 1942 exposed to waterborne cadmium and copper.

The use of physiological parameters as sensitive indicators of toxic stress from exposure to different pollutants is an important issue to be studied. Hyalella curvispina is a Neotropical amphipod often used in ecotoxicological evaluations. This work aimed to quantify biochemical responses of ecological importance in H. curvispina males under stress exposure to sublethal concentrations of waterborne copper (Cu) and cadmium (Cd); in order to obtain basic physiological data as indicators of early effect on this species, on track to its standardization. In order to evaluate the physiological, biochemical and energetic status of the exposed animals, the following endpoints were selected: content of glycogen, total proteins, total lipids, triglycerides, glycerol, arginine, arginine phosphate, levels of lipid peroxidation (TBARS), and Na(+)/K(+)ATPase, catalase (CAT) and superoxide dismutase (SOD) activities. Our results show that the concentrations of Cu (135 and 175 µg/L) and Cd (6.5 and 10.5 µg/L) tested altered most of the biochemical variables measured (glycogen, total proteins, total lipids, triglycerides, arginine phosphate, TBARS, and SOD and Na(+)/K(+)ATPase activities). In addition, neither the levels of glycerol and arginine nor CAT activity were affected by exposure to either metal. Energy metabolism was similarly affected both by exposure to Cu and exposure to Cd. The results obtained show the existence of an energy imbalance associated with oxidative damage, suggesting a comprehensive response. This work represents a first contribution of the evaluation of the effect of two heavy metals in some parameters of oxidative stress and energy metabolism of H. curvispina males. The results indicate these parameters can provide a sensitive criterion for the assessment of early ecotoxicological effects of Cu and Cd in laboratory assays, on a native species representative of the zoobenthic and epiphytic communities of South America.

Biomonitoring toxicity of natural sediments using juvenile Hyalella curvispina (Amphipoda) as test species: evaluation of early effect endpoints.

The utility of early effect endpoints as biomarkers of ecotoxicity of natural sediments in water-sediment static system was investigated. The particular goal was to evaluate the ecotoxicity of the sediment samples from La Choza stream, located in upper basin of the Reconquista river, the second most polluted river of Argentina. Native juveniles Hyalella curvispina were used as test organisms evaluating survival, growth, oxidative stress parameters (SOD; CAT, TBARS) and the electron transport system (ETS) activity as early toxic effect. This study used methodologies and techniques that allow the assessment of sediment pollution with a native species as test organism and provided data to discuss the viability of sublethal endpoints as tools for freshwater sediment assessment. In spring and in summer two ten-day series of whole-sediment assays were conducted simultaneously: (a) standard assays and (b) biomarkers assays. A control sediment was ran simultaneously in which no--effect on survival was measured. In summer there was a significant increase in length and biomass in both exposed and control groups. In spring an inhibitory effect on growth and an increase in oxidative damage with a concomitant rise in antioxidant defenses, was observed in animals exposed to La Choza sediment. ETS measurement indicated a significant depression of metabolic activity of amphipods exposed to contaminated sediments. The measured biomarkers represent the first record for juvenile H. curvispina exposed to polluted natural sediments under standardized laboratory conditions. The used bioanalytical tools demonstrated higher sensitivity and a more accurate assessment of the effects than those obtained by the standard tests of survival and growth. We propose their adoption in biomonitoring of freshwater sediment toxicity.

Cnesterodon decemmaculatus juveniles as test organisms in toxicity assessment: cadmium case.

The poeciliid Cnesterodon decemmaculatus is one of the native species of southern South America recently recommended for use as a test species in biomonitoring. Therefore, it is important to characterize its responses to stress conditions caused by pollution. The aim of this work was to determine the toxicity of the reference toxicant cadmium (Cd) and to evaluate the lethality response of juveniles of C. decemmaculatus exposed to an environmental sample with a high degree of pollution (Luján River, Buenos Aires, Argentina). The LC50 values at 24 and 96 h were 6.00 and 2.27 mg Cd/L, respectively. The uptake of Cd was significantly greater in the first 24 h in relation to the total time of exposure in the bioassay. The toxicity of the water was in agreement with the level of contamination. A Cd contaminant pulse exerted an important additive effect on the toxicity of the environmental sample. The results provide information regarding the sensitivity of a native species to be used as a test organism in environmental monitoring.

Cadmium toxicity assessment in juveniles of the Austral South America amphipod Hyalella curvispina.

Hyalella curvispina is representative of zoobenthic communities in Austral South America. It is taxonomically close to Hyalella azteca and abundant in fresh water bodies of the pampasic region of Argentina. It is usually used as test organism in ecotoxicological studies at a regional level, and there is a strong concern to increase the knowledge of both their biology and their sensitivity to different toxic agents. The aim of the present work was to assess the effects of cadmium on H. curvispina juveniles exposed to concentrations expected in the water bodies of the distribution area of the species. Survival, growth and cadmium body burden were evaluated in aqueous and solid matrices under fixed experimental conditions. Animals were exposed in ten-day static toxicity bioassays to 2.5, 5.25 and 11.25 µg Cd/L for the aqueous-phase bioassays, and to 0.85, 2.8 and 5.6 mg Cd/Kg dry sediment for the solid-phase bioassays. In water only assays, the animals exposed to 11.25 µg Cd/L showed a significant decrease in survival and growth. In the sediment bioassays, no effect was observed on survival, and weight was significantly reduced at the highest concentration. Cadmium uptake was concentration dependent for both assay matrices and one order of magnitude higher in the aqueous medium than in the solid matrix. Results indicate that juveniles of H. curvispina are sensitive to cadmium concentrations expected in their environment and thus confirm their importance as test organisms for ecotoxicity assessment in water bodies within the distribution area of the species.

Evaluation of the Acute Effects of Arsenic on Adults of the Neotropical Native Fish Cnesterodon decemmaculatus Using a Set of Biomarkers.

Neotropical fish Cnesterodon decemmaculatus were exposed to different sublethal concentrations (0.5, 1.0 and 5.0 mg As/L) of sodium arsenite (As III) to determine the median lethal concentration (LC50; 96 h) and to evaluate the response of a set of biomarkers (genotoxic, behavioral, biochemical, and metabolic). At the end of the exposure (96 h), fish were video-recorded for behavior assessment. We used the micronucleus and nuclear abnormality tests and the comet assay in peripheral blood as genotoxicity biomarkers. In regard to biochemical and metabolic biomarkers, we dissected the brain for acetylcholinesterase (AChE) activity; the liver for glutathione-S-transferase (GST) and catalase (CAT) activity and glutathione content (GSH); the gills for GSH content; and muscle for AChE, energy metabolism of lipids, carbohydrates, and proteins, and the electron transport system activity of the mitochondrial chain. We calculated an index using metabolic biomarkers, to determine the cellular energy allocation. The LC50 value was 7.32 mg As/L. The As affected some swimming parameters in females. No significant differences in micronucleus were found compared with the control, whereas nuclear aberrations increased significantly at 1.0 and 5.0 mg As/L. The genomic damage index and the percentage of cells with DNA damage (measured by the comet assay) showed a significant increase in the As-treated groups, and this technique was the most sensitive for detecting genotoxic damage. The As affected the antioxidant system (mainly GSH, CAT, and GST) and reduced the lipid content. A preliminary baseline was generated for the response of C. decemmaculatus exposed to sublethal concentrations of As, when it alters swimming behavior and the antioxidant system, has genotoxic effects, and reduces lipid content. Environ Toxicol Chem 2022;41:1246-1259. © 2022 SETAC.

Cadmium toxicity in tadpoles of Rhinella arenarum in relation to calcium and humic acids.

Bioassays were carried out to study the differences in cadmium (Cd) toxicity to premetamorphic tadpoles of Rhinella arenarum, in aqueous solutions with variable contents of calcium in the presence and absence of humic acids, and to analyze the relationship between the free Cd(2+) ion concentrations calculated by chemical modeling and the biological results. The correlation analysis of the free Cd(2+) concentration calculated by chemical speciation and the analytical Cd yielded a direct relationship between the degree of toxicity and the slope value. The lowest slope was obtained from the treatments with lowest free Cd(2+) ion concentration and lowest toxicity, whereas the highest slope was obtained from the most toxic treatment. At comparable concentrations of free Cd(2+), intralarval Cd increased as the Ca in the solution decreased. At equal contents of Ca, in the presence of humic acids, the content of Cd in larvae was higher and the toxicity values lower. The results obtained in this study show that waterborne Ca could offer some protection from metal uptake and accumulation by competitive inhibition in the uptake mechanism that involves active transport via cell membrane. In the systems with humic materials, a certain proportion of the Cd present in the solution was associated to them and thus became less bioavailable.

Non-point contamination homogenizes the water quality of pampean streams.

The aim of this research was to study the effects on streams water quality of non-point contamination as agriculture and cattle farming activities at a basin with pampean characteristics located at the upper Reconquista River Basin. Eight reaches with different uses in their neighboring zones were selected with the proposed to detect differences at the water quality among them. SRP range was 0-0.60 mgP.PO (4) (-3) /L, ammonia 1-137.3 µgN-NH4(+)/L and nitrate 0-4.15 mgN-NO(3) (-)/L. There was high similitude and homogeneous physicochemical characteristics at the different reaches of the streams. The high levels of dissolved nutrients showed similar eutrophication conditions at the streams.

Acute toxicity of cadmium to freshwater fishes and its relationship with body size and respiratory strategy.

Acute toxicity assays in freshwater fishes are used in diverse local and regional regulations. Lethality is a complex biological process, depending on both extrinsic and intrinsic factors. The extrinsic parameters (pH, temperature, hardness and alkalinity, among others) have been widely studied and their influence on toxicity has been well characterized. In contrast, less attention has been given to intrinsic parameters (body size, sex, life habits) and their influence on toxicological sensitivity is poorly known. This work is focused on the effect of intrinsic parameters on lethality. For this purpose, we systematically reviewed experimental studies that reported data on acute lethality (LC50-96 h) of cadmium to freshwater fishes. We studied the allometric relationship between reported body weight and lethality, and the influence of the respiratory strategy and adaptation to extremely low-ionic strength environments on the sensitivity of fishes to cadmium. We observed a strong relationship between LC50-96 h and body weight. The fish group adapted to low-ionic strength water (OF) showed the highest sensitivity to cadmium, with the allometric constants being a = 0.0045 and b = -1.11, while the group of air-breathing fishes such as Channa marulius and Hepteroneustes fossillis exhibited the lowest sensitivity, with the allometric constants being a = 42.04 and b = -0.44.The effect of the intrinsic parameters can be easily combined with known toxicological models, thus contributing to the construction of models suitable for a wider range of species.

Sensitivity of preparasitic stages of Chordodes nobilii (Gordiida, Nematomorpha) to malathion.

The largest part of the life cycle of Gordiida, known as horsehair worms, occurs in aquatic environments usually affected by agricultural activities. The free-living adults reproduce in freshwater environments, where preparasitic larvae undergo development. Since malathion is an insecticide used in the distribution area of Chordodes nobilii, the aim of this study is to evaluate the effect of malathion concentrations which might be expected in the environment on preparasitic stages of this species. The embryonic development and the viability of larvae were analyzed after a short-term exposure to malathion concentrations ranging between 36 and 220 microg a.i./l. Embryo development was inhibited at 220 microg a.i./l and the infective capacity of larvae derived from malathion-exposed eggs was significantly decreased starting from the lowest concentration. Larvae developed from malathion-exposed eggs exhibited malformations. Directly exposed larvae also showed decreased infectivity since the lowest assayed concentration. Our results indicate that a short-term exposure to malathion at levels potentially present in the surface water in environments inhabited by Chordodes nobilii affects significantly its preparasitic stages and the infective capacity of parasitic larvae.

Histological, Genotoxic, and Biochemical Effects on Cnesterodon decemmaculatus (Jenyns 1842) (Cyprinodontiformes, Poeciliidae): Early Response Bioassays to Assess the Impact of Receiving Waters.

In the present study, the toxicity of receiving waters from a highly polluted urban watercourse, the Reconquista River, Argentina, collected at a dam in the upstream part of the river was evaluated. Cnesterodon decemmaculatus, a widely distributed fish species in Pampasic rivers proposed for use in ecotoxicological evaluations, was used as a test organism. A 96-h acute toxicity bioassay with river water quality which has been characterized as moderately contaminated was performed. The treatment groups were (1) whole surface river water; (2) whole surface river water with 2 mg Cd/L added as a simulated metal contaminant pulse; (3) a negative control using reconstituted moderately hard water (MHW); (4) a metal positive control, MHW + 2 mg Cd/L; and (5) a positive genotoxicity control, MHW + 5 mg Cyclophosphamide/L (CP). The condition factor rate, micronuclei frequency, and comet assay from peripherical blood, structural changes of the gill arrangement by scanning electron microscope (SEM) analysis, histopathological changes in the liver and the glutathione-S-transferase, catalase, superoxide dismutase, glutathione, and protein content from the body midsection (viscera) were evaluated. According to our results, for short term exposure, SEM analyses of gills and liver histopathological analyses could be useful tools for the evaluation of target organ damage as well as comet assays for DNA damage. We propose that the 96-h laboratory bioassay protocol described is useful for monitoring the deterioration of water quality employing the teleost C. decemmaculatus and that the microscope analysis of gills and liver as well as the comet assay methodology could be sensitive endpoint indicators.

Use of integrated biomarker indexes for assessing the impact of receiving waters on a native neotropical teleost fish.

In the field of aquatic ecotoxicology, indexes obtained from a battery of biomarkers have proved to be a useful tool for assessing quantifiable and integrated health responses of organisms exposed to pollutants. The objective of this work was to evaluate the effects of exposure to the Reconquista River water (RR) on adults of Cnesterodon decemmaculatus using different integrated indexes. We conducted a 12-d laboratory assay involving the exposure of fish to RR, a negative control (moderately hard water - MHW medium), and a positive control (for genotoxicity with MHW + Cyclophosphamide, CP). There were measured metabolic (food intake and specific assimilation, specific metabolic rate, oxygen extraction efficiency, ammonia excretion, and ammonia quotient), genotoxic (comet assay, micronucleus test, and nuclear abnormalities), morphological variables (total length, body and liver weight) and biochemical variables (Electron Transport System - ETS, Acetylcholinesterase activity - AChE, Catalase - CAT, Glutathione-S-transferase - GST, Glutathione content - GSH and tissue proteins). These variables were grouped into different indexes: morphological (Condition Factor - K and Liver Somatic Index-LSI), metabolic (Scope for Growth-SFG), genetic damage (GDI) and integrated biomarker response - IBR (AChE brain, CAT, GST and GSH liver, GSH gills, ETS muscle) indexes. Results indicated that RR water induced metabolic, biochemical and genetic damages. The SFG, GDI and IBR were suitable to assess the effects of exposure to an environmental sample in an integrated approach, reducing uncertainty due to inherent biomarker variability. These indexes have emerged as promising tools for environmental monitoring studies.

Toxicity of the herbicide glyphosate to Chordodes nobilii (Gordiida, Nematomorpha).

Nematomorpha (horsehair worms) is a poorly known group of worm-like animals similar to nematodes. Adults are free-living and reproduction takes place in freshwater environments, where preparasitic larvae undergo development. All species have a parasitic juvenil stage and infection may result in the host's death, insects being the most frequent host. Most of the life cycle occurs in freshwater environments, which are often contaminated by different pollutants. Based on the lack of information on the toxicity of herbicides to horsehair worms, the objective of this study is to evaluate the effect of different concentrations of glyphosate (technical grade and formulated product) on Chordodes nobilii (Gordiida, Nematomorpha). Bioassays were performed with embryos and larvae (preparasitic stages), and adults (postparasitic stage). Test organisms were exposed for a short period of time to concentrations ranging between 0.1 and 8 mga.e.l(-1) of glyphosate (technical and formulated). Although embryo development was not inhibited, there was a significant decrease in the infective capacity of larvae derived from eggs that had been exposed to >or= 0.1mg/l. Similar results were obtained for directly exposed larvae. No differences in toxicity were detected between the active ingredient and formulated product. Adult exposed for 96 h to 1.76 mgl(-1) formulated Gly shown a mortality of 50%. Results indicate that C. nobilii is affected at glyphosate concentrations lower than those expected to be found in freshwater environments and those specified in the legislation.

Susceptibility of Chordodes nobilii (Gordiida, Nematomorpha) to three pesticides: Influence of the water used for dilution on endpoints in an ecotoxicity bioassay.

The increased use of pesticides during recent years necessitates a reevaluation of the effect of those compounds by extending the range of nontarget species commonly used in risk assessment. In the present work, we thus determined the impact of the pesticides glyphosate, carbendazim, and malathion on the parasite Chordodes nobilii in both natural and reconstituted freshwater as the assay medium and tested the sensitivity of three of this species's ecologically relevant parameters-e. g., embryo nonviablity and the infective capability of larvae exposed for 48 or 96 h either in ovo or after hatching via the infection index mean abundance-to compare those parameters to data from previous trials with reconstituted freshwater. In natural-freshwater assays, at environmentally relevant concentrations, all three pesticides inhibited the preparasitic-stage endpoints; with carbendazim being the most toxic pesticide and the subsequent infectivity of larvae exposed in ovo the most sensitive endpoint. In general, the 50%-inhibitory concentrations assayed in reconstituted freshwater were higher than those obtained in natural freshwater, indicating a certain protective effect; whereas the maximal toxicity of the three pesticides in both aqueous environments was essentially similar. The sensitivity of C. nobilii to these agents demonstrated that this species is one of the most susceptible to toxicity by all three pesticides. These findings with the assay methodology provide relevant information for a future assessment of the risk of toxicity to aquatic ecosystems and furthermore underscore the need to include parasitic organisms among the nontarget species canvassed. We also recommend that in the bioassays in which the risk assessment is carried out, water from a nontarget species's natural environment be used in parallel in order to obtain more conclusive results.

Assessment of the pollution impact on biomarkers of effect of a freshwater fish.

Changes in biomarkers of fish captured from stressed environments may represent a reliable tool in revealing sublethal effects of the pollutants found in aquatic ecosystems. The response patterns of selected biochemical and morphological variables biomarkers of effect were assessed in adult females of an indigenous teleost Cnesterodon decemmaculatus, caught at a polluted site (San Francisco) of the Reconquista river (Buenos Aires, Argentina). Combined field-caging experiments with controlled laboratory exposure to clean media were performed. The biochemical parameters measured were specific activities of gill (Na+ + K+)-ATPase, liver AlaAT and AspAT, and brain AChE; LSI and CF were also calculated. The changes in gill (Na+ + K+)-ATPase and liver AlaAT activities of fish captured in the field in most cases were reversible after transfer to clean media. The results were interpreted in association with the physicochemical profile of the water samples taken simultaneously with the capture of the fish. Results suggested the suitability of the test species used as tools in environmental monitoring programs of risk assessment.

Biomarkers of a native fish species (Cnesterodon decemmaculatus) application to the water toxicity assessment of a peri-urban polluted river of Argentina.

Environmental monitoring by means of biomarker parameters assessed in different species is a useful tool. It has the advantage of providing a quantitative response as well as valuable information of ecological relevance on the chronic adverse effects caused by water pollution. The aim of this study was to assess the response of biochemical and physiological parameters of Cnesterodon decemmaculatus, a native teleost, simultaneously caught in two sites of Reconquista river, a highly polluted peri-urban river. This study compared the measured parameters with that of specimens of the same species captured in an unpolluted body water, and correlated the detected changes with the physicochemical profile of the water at each site. A comparison was made of selected parameters of gill, brain and liver and of somatic indices of fish collected from polluted and reference sites. The main parameters whose changes allowed to discriminate between sampling sites were gill (Na(+),K(+))-ATPase, brain acetylcholinesterase (AChE) and liver aminotransaminases activities; tissues' protein content and liver somatic index (LSI) were also sensitive biomarkers in brain and liver, respectively. The results showed that the response of the measured biomarkers allowed for the differentiation of sampling sites according to their water quality and confirmed that Cnesterodon decemmaculatus may be a useful test organism for the biomonitoring of freshwater environments. In addition, the simultaneous measurement of the physicochemical parameters of the water samples showed a good correspondence between the biomarkers responses and the environmental chemical stress conditions.

Infectivity of Chordodes nobilii larvae (Gordiida: Nematomorpha) / Infectividad de las larvas de Chordodes nobilii (Gordiida: Nematomorpha)

AbstractThe gordiids are freshwater representatives of the parasite phylum Nematomorpha that function as a link between aquatic and terrestrial ecosystems. In recent years, different ecotoxicologic studies have been made with the South-American gordiid species, Chordodes nobilii, that have demonstrated the capacity of this group to act as a bioindicator of contamination. Despite the Gordiida's ecologic relevance, further studies are still needed to elucidate different aspects of the biology of the class, and among those, the infective capacity, a parameter that can be evaluated by the infection index mean abundance (IIMA). A knowledge of the intrinsic variability in the infective capacity of C. nobilii would warrant priority in order to establish, the range of acceptable responses for normal or standard conditions in the laboratory, and, to compare the criteria among different assays. The objective of this study was to establish a baseline value for the infective capacity for C. nobilii larvae, under controlled laboratory conditions, by employing the IIMA as the evaluation parameter. To that end, we analyzed the infective capacity of C. nobilii larvae that had hatched from different strings of eggs laid in the laboratory by a total of 12 females. The C. nobilii adults were collected from streams within the Argentina Sauce Grande basin, between 2006 and 2009. Once in the laboratory, after mating, the females were placed in individual containers for oviposition. The egg strings obtained from each female were cut in 3 mm long segments; and when free larvae were observed, the segments (N= 90) were placed together with 30 Aedes aegypti larvae for evaluation of the gordiids' infective capacity. After 72 h, the mosquito larvae were observed by microscopy in order to quantify the C. nobilii larvae in body cavities. The IIMAs were calculated as the total number of C. nobilii larvae present divided by total number of A. aegypti larvae examined. For analysis of the IIMAs obtained, the data were grouped according to the female who made the original ovoposition. Our results enabled the corroboration of an ample range of responses in the infective capacity of this species, a characteristic that would normally be linked to the progenitors originating the hatch. Because this relationship prevents the establishment of a baseline for making comparisons among assays with gordiids, through the IIMA as a response parameter, we recommend expressing the IIMA values in each assay relative to their respective controls. These findings also provide evidence for the greater success in infections by certain members of the progeny over others. Finally, on the basis of the results obtained from this study, we stress the relevance of the use of the IIMA as a decisive aspect to be considered in different studies on the biology of Gordiida. Rev. Biol. Trop. 65 (1): 1-8. Epub 2017 March 01.

ResumenLos gordiidos son representantes dulceacuícolas del Phylum parásito Nematomorpha que actúan como un enlace entre ecosistemas acuáticos y terrestres. En años recientes, diferentes estudios ecotoxicológicos se han desarrollado con una especie sudamericana de gordiido, C. nobilii, que ha demostrado la capacidad de este grupo de actuar como bioindicador de contaminación. A pesar de su evidente importancia ecológica, aún se necesitan realizar estudios para dilucidar distintos aspectos de su biología, entre estos, la capacidad infectiva, un parámetro que puede evaluarse utilizando el Índice de Infección Abundancia Media (IIMA). El conocimiento de la variabilidad intrínseca en la capacidad infectiva de C. nobilii merece prioridad con el objeto de establecer el ámbito de respuesta aceptable para condiciones normales o estándar en el laboratorio, y que permita comparar los resultados entre distintos ensayos. El objetivo de este estudio es establecer la línea de base de la capacidad infectiva del gordiido C. nobilii en condiciones controladas de laboratorio, empleando el IIMA como parámetro de evaluación. Con este fin, se analizó la capacidad infectiva de larvas de C. nobilii que eclosionaron de diferentes cordones de huevos depositados por un total de 12 hembras, mantenidas en laboratorio. Los adultos de C. nobilii fueron recolectados de arroyos de la cuenca argentina Sauce Grande, entre 2006 y 2009. Una vez en el laboratorio, después de la cópula, las hembras se ubicaron en recipientes individuales a la espera de la oviposición. Los cordones de huevos obtenidos de cada hembra se cortaron en segmentos de 3 mm de longitud; y cuando las larvas libres fueron observadas al microscopio, los segmentos (N= 90) fueron ubicados junto con 30 larvas de Aedes aegypti para evaluar la capacidad infectiva del gordiido. Después de 72 h, las larvas del mosquito fueron observadas al microscopio para contabilizar las larvas de C. nobilii en las cavidades corporales. El IIMA fue calculado como el número total de larvas de C. nobilii presentes dividido entre el número total de larvas de A. aegypti examinadas. Para el análisis de los IIMAs obtenidos, los datos fueron agrupados de acuerdo a la hembra que hizo la oviposición. Nuestros resultados permiten corroborar un amplio rango de respuesta en la capacidad infectiva de esta especie, que estaría vinculada al origen de la camada. Debido a que no se pudo establecer una línea de base para realizar comparaciones entre estudios en los gordiidos utilizando el IIMA como parámetro de respuesta, se aconseja relativizar los valores de los IIMAs a sus respectivos controles. Estos resultados también pusieron en evidencia la ventaja en el éxito de infección de algunas progenies sobre las restantes. Finalmente, con base en los resultados obtenidos a partir de este estudio se plantea la importancia del uso del IIMA como punto final a considerar en distintos estudios sobre la biología de los gordiida.

Validation test with embryonic and larval stages of Chordodes nobilii (Gordiida, Nematomorpha): sensitivity to three reference toxicants.

Chordodes nobilii is a parasite whose pre- and postparasitic stages are found in different types of freshwater bodies. Due to the peculiarities of its life cycle, it acts as a link between freshwater bodies and terrestrial ecosystems. There is little toxicological information on the group Gordiida. It is only known that embryos and larvae of C. nobilii are sensitive to glyphosate and malathion at relevant concentrations in the environment. On this basis, the aims of this study were to characterize the sensitivity of the pre-parasitic stages of C. nobilii to three reference toxicants: sodium dodecyl sulfate (SDS), cadmium chloride and potassium dichromate (Cr(6+)), and to validate a previous experimental protocol for ecotoxicological risk assessment. The protocol involved acute exposure of early embryonic stages and larvae to the three toxicants for 96 h and 48 h, respectively. Embryo development was inhibited only by Cr(6+) which presented a IC(50) of 0.71 mg Cr(6+)L(-1). The development of the eggs exposed to SDS and those exposed to cadmium chloride showed no differences as compared to that of controls. However, the infective capacity of larvae derived from the eggs exposed to the three toxicants was lower than that of controls. Larval survival was affected even at the lowest concentration of the three toxicants assayed. In relation to other freshwater organisms, C. nobilii can be characterized as an organism medium to highly sensitive to the toxicants tested.