Microcystin and pyriproxyfen are toxic to early stages of development in Rhamdia quelen: An experimental and modelling study

Developmental toxicity of pyriproxyfen induces changes in the ultrastructure of neural cells and in the process of skull ossification

Some studies relate the use of pyriproxyfen (PPF) in drinking water with damage to embryonic neurodevelopment, including a supposed association with cases of microcephaly. However, the effects on neural cells and skull ossification in embryos remain unclear. This study aims to investigate the effects of PPF on the structure and ultrastructure of brain cells and its influence on the skull ossification process during embryonic development. Chicken embryos, used as an experimental model, were exposed to concentrations of 0.01 and 10 mg/l PPF at E1. The findings demonstrated that PPF led to notable ultrastructural alterations such as reduced cilia and microvilli of ependymal cells and damage to mitochondria, endoplasmic reticulum, Golgi bodies, and cell membranes in neural cells. The frequency of changes and the degree of these cell damage between the forebrain and midbrain were similar. PPF induced a reduction in fox3 transcript levels, specific for differentiation of neurons, and a reduction in the NeuN protein content related to mature neurons and dendritic branches. PPF impacted the ossification process of the skull, as evidenced by the increase in the ossified area and the decrease in inter-bone spacing. In conclusion, this study highlights the ability of PPF to affect neurodevelopmental processes by inducing ultrastructural damage to neural cells, concomitant with a reduction in NeuN and fox3 expression. This detrimental impact coupled with deficiencies in skull ossification can prevent the proper growth and development of the brain.

Pyriproxyfen Contamination in Daphnia magna: Identifying Early Warning Biomarkers

Pyriproxyfen is an insecticide currently employed in numerous countries for the management of agricultural and indoor pests. Several studies indicate that this insecticide has been detected in multiple rivers, with concentrations reaching as high as 99.59 ng/L in the Júcar River in Spain. Therefore, the determination of some biochemical and genetic effects of this insecticide on aquatic organisms could serve as an early warning mechanism to identify potential disruptions in various biomarkers. Based on this, Daphnia magna organisms were exposed to pyriproxyfen sublethal concentrations for 21 days. Some biochemical parameters, including cholesterol, triglycerides, glucose, lactate, and LDH activity, were determined. Additionally, some genetic biomarkers associated with oxidative stress, heat shock proteins, lipid metabolism, hemoglobin, metallothioneins, and vitellogenin synthesis were evaluated in daphnids exposed to the insecticide for 21 days. LDH activity increased significantly in those daphnids exposed to the highest insecticide concentration (14.02 µg/L), while cholesterol levels decreased significantly. In contrast, glucose, total proteins, and triglycerides remained unaffected in D. magna exposed to pyriproxyfen. On the other hand, exposure to the insecticide led to notable alterations in gene expression among individuals. Specifically, genes associated with lipid metabolism and reproduction exhibited a significant reduction in gene expression. Fabd expression was decreased by approximately 20% in exposed daphnids, while vtg expression was suppressed as much as 80% when compared to control values. Furthermore, it was observed that the hgb1 and hgb2 genes, associated with hemoglobin synthesis, exhibited significant overexpression. Notably, the dysfunction observed in both hemoglobin genes was linked to an increase in pigmentation in Daphnia magna during the course of the experiment. These alterations in gene expression could serve as effective indicators of early contamination even at low pesticide concentrations.

Multigenerational effects of the insecticide Pyriproxyfen and recovery in Daphnia magna

In the present study, an ecotoxicological approach to the evaluation of the insecticide Pyriproxifen in the crustacean Daphnia magna was done. Acute toxicity tests (48 h), feeding behavior test (5 h) and chronic toxicity test (21 days) were carried out on a parental daphnid generation (F0). Pyriproxifen D. magna EC50 value in our experimental conditions was 336.47 μg/L. Based on this result, sublethal test concentrations were selected for the feeding study and the F0 chronic experiment. Filtration and ingestion rates of D. magna exposed animals did not show any significant difference respect to control daphnids. However, daphnids from the parental F0 generation when exposed to the insecticide during 21 days showed a decreased in all the reproductive parameters tested (mean total neonates per female, mean brood size, time to first brood, and mean number of broods per female) as well as in the population statistic growth rate (r), although survival was not affected. On the other hand, offspring from F0 females exposed to the highest Pyriproxifen concentration (14.02 μg/L) were separated in two F1 generation experiments. One group was transferred during 21 days to a medium free of toxicant (F1 generation-TC group) while the other group was exposed during 21 days to the same insecticide concentration as their mothers (14.02 μg/L) (F1 generation-TT group). Results from both experiments determined a decreased in most of the reproductive parameters which was higher in the F1-TT group, although some of them were recovered in the F1-TC group. On the other hand, the morphological analysis of the daphnids showed that the coloration pattern was altered in the daphnids exposed to the insecticide, together with a significant size decreased, and neonates from F0 progeny with the same morphological abnormality. Finally, we determined that the insecticide caused the appearance of males among the offspring generated by the F0.

Sublethal effects of the herbicides atrazine and glyphosate at environmentally relevant concentrations on South American catfish (Rhamdia quelen) embryos

The objective of this work was to evaluate the effects following exposure (96 h) of South American catfish (R. quelen) embryos to active ingredients and commercial formulations from atrazine and glyphosate, isolated and in mixtures, at environmentally relevant concentrations. While the survival rates were not affected, sublethal effects were evidenced after exposure. The most frequent deformities were fin damage and axial and thoracic damage. The mixture of active ingredients caused an increase in SOD and GST, differing from the treatment with the mixture of commercial formulations. The activity of AChE was significantly reduced following the treatment with the active ingredient atrazine and in the mixture of active ingredients. In general, herbicide mixtures were responsible for causing more toxic effects to R. quelen embryos. Therefore, these responses showed to be suitable biomarkers of herbicides' exposure, in addition to generating more environmentally relevant baseline data for re-stablishing safety levels of these substances in aquatic bodies.

From molecular endpoints to modeling longer-term effects in fish embryos exposed to the elutriate from Doce River

Sediments represent a major sink and also a main source of contaminants to aquatic environments. An environmental disaster from a mining dam breakage in 2015 in South-East Brazil re-suspended complex mixtures of chemicals deposited in the sediment, spreading contaminants along the Doce River Basin (DRB) major river course. While high levels of contaminants in sediment were well described, toxicological effects in aquatic organisms were poorly investigated. Thus, the effects of these potentially toxic chemicals were assessed in the present study through different endpoints (biochemical to populational levels) in fish embryos of the South-American silver catfish exposed to elutriates from different sites of the DRB. Despite no significant mortality observed, our results showed that exposure to the elutriates, especially those from the closest site to the dam collapse, caused higher deformities rates and DNA damage in the fish embryos than in the control group. Multivariate analysis showed that these sublethal effects may be related to the high levels of metals introduced by mining activities, compromising long-term survival and reproduction success. In addition, it was possible to observe the influence of other sources of pollutants along the river. According to our data, the mathematical model simulated a significant impact on the population density at longer-term exposure, for the sites that showed the most prominent toxicity responses. The fish embryo toxicity test proved to be an effective assay to assess the ecotoxicological effects of the pollutants from a major river contaminated by a mining dam collapse and showed that the survival rate per se was not a suitable endpoint to assess the toxicity of the pollutants. As a consequence, we contributed to shed a light on a potential underestimated impact of pollutants in sediments of the DRB on the native organisms at distinct biological levels of organizations.

Organic and inorganic pollutants in Jordão and Iguaçu rivers southern Brazil impact early phases of Rhamdia quelen and represent a risk for population

The Iguaçu River basin presents high ecological importance due to its expressive endemic ichthyofauna rate, but chemical pollution may threat this biodiversity. Jordão River is one of the main tributaries of Iguaçu River and contribute to this pollution status, since it drains large agricultural areas receiving domestic and industrial effluents before flowing into the Iguaçu River. The objective of the current study was to evaluate the toxic effects of the Iguaçu, Jordão, and the combination of their waters to the embryo-larval phase of R. quelen, investigating the consequences to the population by means of mathematical modelling. R. quelen fertilized eggs were exposed for 96 h to water samples from Iguaçu River upstream (IR), Jordão River (JR), and downstream of both rivers (MR). The analysis of micropollutants in the water showed that JR presented the most complex mixture of substances and elements, followed by IR, while MR showed the lower number of micropollutants detected. Survival rate was not a sensitive endpoint, while the deformity indices were higher in individuals exposed to water from the three studied sites. Superoxide dismutase activity was increased in MR, while non-protein thiol levels were reduced in MR and JR showing the antioxidant mechanism activation. The mathematical modelling revealed that fish exposed to JR would lead to the greater population reduction (46.19%), followed by IR (40.48%) and MR (33.33%). Although the results showed toxicity in all studied sites, the JR site is the most impacted by micropollutants but decrease its toxicity after dilution with Iguaçu River.

Evaluation of DNA Damage, Biomarkers of Oxidative Stress, and Status of Antioxidant Enzymes in Freshwater Fish (Labeo rohita) Exposed to Pyriproxyfen

Pyriproxyfen (PPF) mimics a natural hormone in insects and disrupts their growth. It is a well-known synthetic insecticide and aromatic juvenile hormone analog frequently used in agriculture and vegetable crops to control various insect species. At present, scanty information is available about the possible potential threats of PPF in aquatic organisms. Therefore, in this study, different toxico-pathologic endpoints of PPF like DNA damage, biomarkers of oxidative stress, and status of antioxidant enzymes were determined in Labeo rohita (freshwater fish). In our study, 60 active, free from any external obvious ailments, same size, age, and body mass were randomly allocated to four glass aquaria (T0-T3) separately containing 100 L water. The fish present in groups T1, T2, and T3 were administered PPF dissolved in water 300, 600, and 900 μg/L for 30 days. Different tissues including the blood and visceral organs were obtained from each fish on days 10, 20, and 30 of the experiment. Results on various morphological and nuclear changes in red blood cells of PPF-exposed Labeo rohita fish including pear-shaped erythrocytes, spherocytes, red blood cells with a blebbed nucleus, micronucleus, and nuclear remnants were significantly increased. Our results on genotoxicity (comet assay) recorded significantly (P ≤ 0.05) increased DNA damage in various tissues of insecticide-exposed fish. The results on oxidative stress profile (reactive oxygen species and thiobarbituric acid reactive substances) and antioxidant enzymes (reduced glutathione superoxide dismutase, peroxidase, and catalase) in multiple tissues of Labeo rohita fish concluded significantly (P ≤ 0.05) higher quantity of biomarkers of oxidative stress and lower concentrations of different antioxidant enzymes in treated fish. Hence, the findings of our experimental research determine that PPF could induce adverse toxic impacts on multiple tissues of Labeo rohita fish.

Does exposure to environmental 2,4-dichlorophenoxyacetic acid concentrations increase mortality rate in animals? A meta-analytic review

The 2,4-dichlorophenoxyacetic acid (2,4-D) is an auxinic herbicide widely used in agriculture that is effective in controlling weeds. It is directly applied to the soil, to ponds or sprayed onto crops; thus, it can progressively accumulate in environmental compartments and affect non-target organisms. The aim of the present meta-analytic review is to investigate the toxic effects of 2,4-D, based on a compilation of results from different studies, which were synthesized to form a statistically reliable conclusion about the lethal effect of potentially ecological concentrations of 2,4-D in several animal species. The search was carried out in the Web of Science and Scopus databases. After the selection process was over, 87 datasets were generated and analyzed. The overall effect has indicated significant increase in the mortality rate recorded for animals exposed to environmental concentrations of 2,4-D compared to the control in the experiment (unexposed animals). The segregation of animals into taxonomic categories has shown that fish and birds presented higher mortality rates after exposure to the investigated substance. The present meta-analysis indicated larval and adult animals were susceptible among the ontogenetic development stages. Juvenile individuals exposed to different 2,4-D concentrations did not show significant difference in comparison to the control. Organisms exposed to 2,4-D immersion were the most impacted compared to those exposed by oral, spray and contact. Animals subjected to commercial formulation presented higher mortality rate than the analytical standard. Thus, 2,4-D can, in fact, increase mortality rate in animals, but it depends on species sensitivity, life stage and exposure route. This is the first meta-analytical study evaluating the mortality rate after 2,4-D exposure in several animal species.

Use of High-Performance Liquid Chromatography-Mass Spectrometry of Adipose Tissue for Detection of Bioaccumulation of Pyriproxyfen in Adults of Lithobates catesbeianus

The aims of the study were: (i) evaluate the efficacy of using amphibian adipose tissue as a valid biomarker of water contaminated by pyriproxyfen; and (ii) verify the use of Lithobates catesbeianus in laboratory experiments as a potential bioindicator for bioaccumulation of pesticide in adipose tissue from amphibians. Adult frogs were exposed to different dilutions (0.002 g/L and 0.02 g/L) of Sumilarv® (pyriproxyfen) over 50 days. The average results of the fortified sample were 108%, indicating that the test method was effective. Adult frogs exposed to the standard dose recommended by the World Health Organization (WHO) showed bioaccumulation of pyriproxyfen in adipose tissue significantly higher than control animals. Lithobates catesbeianus proved to be an effective bioindicator and the adipose tissue was an efficient biomarker to bioaccumulation of pyriproxyfen. We conclude that high-performance liquid chromatography-mass spectrometry was effective measuring pyriproxyfen bioaccumulation in adult amphibians.

Pyriproxyfen exposure induces DNA damage, cell proliferation impairments and apoptosis in the brain vesicles layers of chicken embryos

Larvicide pyriproxyfen (PPF), used in drinking water reservoirs to control Aedes mosquitoes, has already been shown as a possible cause of congenital anomalies in the central nervous system. However, the neurotoxic effects of PPF on the development of vertebrate embryos are still underexplored. Thus, the aim of this study was to investigate the effects of PPF on the morphometric parameters of the head and brain, as well as on the cell layers of the forebrain and midbrain, using embryos of Gallus domesticus as a model. Two sublethal PPF concentrations (0.01 mg/L and 10 mg/L), as defined by a survival curve, were tested. Analysis of the biometry of embryos showed significant reduction in body and brain mass and also in measurements of the head and brain. A reduction in cell layer thickness of the forebrain and midbrain was observed, accompanied by a reduction in the numerical density of cells per area. Changes in brain and head sizes and in the thickness of the cell layers of the forebrain and midbrain were significant at 10 mg/L PPF. Notably, PPF caused DNA doublestrand breaks and induced apoptosis in embryos exposed to 10 mg/L, which were accompanied by a reduction in cell proliferation. Regarding neuronal and glial differentiation, no changes were observed in the number of neurons and glial cells on the analyzed layers. Furthermore, PPF did not impact the head ossification process. These findings reveal that PPF is a strong stressor for neurodevelopment, causing damage to the cell architecture of brain vesicles.

Effects of harmful algal blooms on stress levels and immune functioning in wetland-associated songbirds and reptiles

Harmful algal blooms (HABs), caused primarily by nutrient input from agricultural runoff, are a threat to freshwater systems worldwide, and are further predicted to increase in size, frequency, and intensity due to climate change. HABs occur annually in the Western Basin of Lake Erie (Ohio, USA), and these blooms become toxic when dominated by cyanobacteria that produce the liver toxin microcystin. Although we are making substantial inroads toward understanding how microcystin affects human health, less is known about effects of microcystin on wildlife exposed to HABs. Wetland-associated songbirds (barn swallows, Hirundo rustica, and red-winged blackbirds, Agelaius phoeniceus) and reptiles (Northern watersnakes, Nerodia sipedon, and painted turtles, Chrysemys picta) were sampled from wetlands exposed to chronically high microcystin levels due to a prolonged HAB event, and from unexposed, control wetlands. Physiological stress levels and several measures of immune functioning were compared between the HAB-exposed and control populations. Physiological stress levels, measured as heterophil:lymphocyte ratios, were higher in barn swallows, red-winged blackbirds, and Northern watersnakes exposed to a chronic HAB compared to unexposed, control individuals, but painted turtles did not differ in physiological stress levels between HAB-exposed and control individuals. Neither barn swallows nor red-winged blackbirds differed in immune functioning between populations, but HAB-exposed watersnakes had higher bactericidal capacity than control snakes, and HAB-exposed painted turtles had lower bactericidal capacity than control turtles. These results suggest that even when HABs do not cause direct mortality of exposed wildlife, they can potentially act as a physiological stressor across several taxa, and furthermore may compromise immune functioning in some species.

Post hatching stages of tropical catfish Rhamdia quelen (Quoy and Gaimard, 1824) are affected by combined toxic metals exposure with risk to population

Toxic metals and silver nanoparticles (AgNPs) are of great importance as pollutants and their frequent use increases the risk of exposure to biota, but few studies have described co-toxic effects in aquatic organisms. In fish, the method using early stages of development are interesting parameters to validate ecotoxicological studies, and more recently, the use of mathematical models has substantially increased the efficiency of the method. Post hatching stages of native catfish Rhamdia quelen were exposed to single or combined mixtures of toxic metals (Mn, Pb, Hg or AgNPs) in order to study its effects. Fertilized eggs were exposed for 24, 48, 72, and 96 h, where hatching and survival rates, malformation frequency, and neuromast structure damages were evaluated. The results showed alterations in hatching rate after single and combined exposure to metals, but mixtures showed effects more severe comparatively with the single exposures. A similar result including a time-dependent effect was observed in survival rates and incidence of deformities. Overall, embryos and larvae were sensitive to toxic metals exposure while the mathematical modeling suggested a population reduction size including risk of local extinction.

Pyriproxyfen induces intracellular calcium overload and alters antioxidant defenses in Danio rerio testis that may influence ongoing spermatogenesis

We investigated the in vitro effects of pyriproxyfen on ionic balance in the testis of the zebrafish by measuring ⁴⁵Ca²⁺ influx. In vivo pyriproxyfen treatment was carried out to study oxidative stress, and conduct morphological analysis of the testis and liver. Whole testes were incubated in vitro with/without pyriproxyfen (10^-12, 10^-9 or 10^-6 M; 30 min) and ⁴⁵Ca²⁺ influx determined. To study pyriproxyfen's mechanism of action, inhibitors/activators of ionic channels or pumps/exchangers, protein kinase inhibitors or a calcium chelator were added 15 min before the addition of ⁴⁵Ca²⁺ and pyriproxyfen. We evaluated the in vivo effects of 7 day exposure to waterborne pyriproxyfen (10^-9 M) on reactive oxygen species (ROS) formation, lipid peroxidation, and reduced glutathione content (GSH), glutathione S-transferase (GST), superoxide dismutase (SOD), catalase (CAT) and γ-glutamyltransferase (GGT) activity. Morphological analyses of the testis and liver were carried out after in vivo exposure of D. rerio to pyriproxyfen. Pyriproxyfen increased ⁴⁵Ca²⁺ influx by opening the voltage-dependent T-type channels (T-type VDCC), inhibiting sarco/endoplasmic reticulum ⁴⁵Ca²⁺-ATPase (SERCA) and the NCX exchanger (forward mode) and by mobilizing calcium from stores. The involvement of potassium channels and protein kinase C (PKC) was also demonstrated in pyriproxyfen-induced intracellular calcium elevation. In vivo pyriproxyfen treatment of D. rerio increased lipid peroxidation, decreased GSH content and increased GST activity in testes, in addition to increasing the number and size of spermatogonia cysts and inducing hepatocyte basophilia and dilation of blood vessels in the liver. The toxicity of pyriproxyfen is mediated by calcium overload, increased lipid peroxidation, and a diminished antioxidant capacity in the testis, due to GSH depletion, and altered spermatogenesis. The development of high basophilia in the liver suggests that pyriproxyfen may have estrogenic activity, possibly acting as an endocrine-disruptor. These findings indicate that these alterations may contribute to pyriproxyfen toxicity and spermatogenesis disruption.

Bacillus spp. metabolites are effective in eradicating Aedes aegypti (Diptera: Culicidae) larvae with low toxicity to non-target species

The growing spread of dengue, chikungunya and Zika viruses demand the development of new and environmentally safe control methods for their vector, the mosquito Aedes aegypti. This study aims to find novel larvicidal agents from mutualistic (endophytic and rhizospheric) or edaphic bacteria that have no action against non-target organisms. Eleven out of the 254 bacterial strains tested were able to kill Ae. aegypti larvae. Larvicidal activity did not depend on presence of cells, since culture supernatants or crude lipopeptide extracts (CLEs) killed the larvae. Bacillus safensis BacI67 and Bacillus paranthracis C21 supernatants were the best performing supernatants, displaying the lowest lethal concentrations (LC50 = 31.11 µL/mL and 45.84 µL/mL, respectively). Bacillus velezensis B64a and Bacillus velezensis B15 produced the best performing CLEs (LC50 = 0.11 mg/mL and 0.12 mg/mL, respectively). Mass spectrometry analysis of CLEs detected a mixture of surfactins, iturins, and fengycins. The samples tested were weakly- or non-toxic to mammalian cells (RAW 264.7 macrophages and VERO cells) and non-target organisms (Caenorhabditis elegans, Galleria mellonella, Scenedesmus obliquus, and Tetrahymena pyriformis) - especially B. velezensis B15 CLE. The biosynthetic gene clusters related to secondary metabolism identified by whole genome sequencing of the four best performing bacteria strains revealed clusters for bacteriocin, beta-lactone, lanthipeptide, non-ribosomal peptide synthetases, polyketide synthases (PKS), siderophores, T3PKS, type 1 PKS-like, terpenes, thiopeptides, and trans-AT-PKS. Purification of lipopeptides may clarify the mechanisms by which these extracts kill Ae. aegypti larvae.

Pyriproxyfen induced impairment of reproductive endocrine homeostasis and gonadal histopathology in zebrafish (Danio rerio) by altered expression of hypothalamus-pituitary-gonadal (HPG) axis genes

Pyriproxyfen (PPF), a broad-spectrum insecticide known to cause reproductive and endocrine disruption in invertebrates, while the data is scarce in aquatic vertebrates. The goal of this study is to investigate the impact of PPF on reproductive endocrine system of male and female zebrafish along hypothalamus-pituitary-gonadal (HPG) axis. In brain, PPF caused significant alteration in the transcripts of erα, lhβ, and cyp19b genes in male and fshβ, lhβ, and cyp19b genes in female zebrafish. The downstream genes of steroidogenic pathway like, star, 3βhsd, 17βhsd, and cyp19a expression were significantly altered in gonad of both sexes. Subsequent changes in circulatory steroid hormone levels lead to imbalance in hormone homeostasis as revealed from estradiol/testosterone (E₂/T) ratio. Further, the vitellogenin transcript level was enhanced in hepatic tissues and their blood plasma content was increased in male (16.21%) and declined in female (21.69%). PPF also induced histopathological changes in gonads such as, reduction of mature spermatocytes in male and vitellogenic oocytes in female zebrafish. The altered E₂/T ratio and gonadal histopathology were supported by the altered transcript levels of HPG axis genes. Overall, these findings provide new insights of PPF in zebrafish reproductive system and highlights for further investigations on its potential risks in aquatic environment.

Harmful Algal Bloom Toxicity in Lithobates catesbeiana Tadpoles

Harmful algal blooms (HAB) have become a major health concern worldwide, not just to humans that consume and recreate on contaminated waters, but also to the fauna that inhabit the environments surrounding affected areas. HABs contain heterotrophic bacteria, cyanobacterial lipopolysaccharide, and cyanobacterial toxins such as microcystins, that can cause severe toxicity in many aquatic species as well as bioaccumulation within various organs. Thus, the possibility of trophic transference of this toxin through the food chain has potentially important health implications for other organisms in the related food web. While some species have developed adaptions to attenuate the toxic effects of HAB toxins, there are still numerous species that remain vulnerable, including Lithobates catesbeiana (American bullfrog) tadpoles. In the current study we demonstrate that acute, short-term exposure of tadpoles to HAB toxins containing 1 µg/L (1 nmol/L) of total microcystins for only 7 days results in significant liver and intestinal toxicity within tadpoles. Exposed tadpoles had increased intestinal diameter, decreased intestinal fold heights, and a constant number of intestinal folds, indicating pathological intestinal distension, similar to what is seen in various disease processes, such as toxic megacolon. HAB-toxin-exposed tadpoles also demonstrated hepatocyte hypertrophy with increased hepatocyte binucleation consistent with carcinogenic and oxidative processes within the liver. Both livers and intestines of HAB-toxin-exposed tadpoles demonstrated significant increases in protein carbonylation consistent with oxidative stress and damage. These findings demonstrate that short-term exposure to HAB toxins, including microcystins, can have significant adverse effects in amphibian populations. This acute, short-term toxicity highlights the need to evaluate the influence HAB toxins may have on other vulnerable species within the food web and how those may ultimately also impact human health.

Fate and ecotoxicological effects of pyriproxyfen in aquatic ecosystems

Pyriproxyfen is an insect growth regulator acting as larvicide against a large spectrum of public health insect pests, especially dipterans. It is also widely used in agriculture and horticulture for the control of many insect species. Disrupting the endocrine system by mimicking the activity of the juvenile hormone, pyriproxyfen interferes with metamorphosis in insects and prevents them from reaching maturity and reproducing. Because the aquatic ecosystems can be directly or indirectly contaminated by pyriproxyfen, the goal of this study was to establish the aquatic ecotoxicological profile of pyriproxyfen and to identify the gaps that need to be filled. Pyriproxyfen is photodegraded quickly in water. In the absence of organic matter, its persistence in aerobic water media is also limited especially with high temperature and sunlight. Analysis of the laboratory and in situ results for more than 60 aquatic algae, plants, invertebrates, and vertebrates shows that the toxicity of pyriproxyfen is highly variable including within a same taxonomical group. Abiotic and biotic factors can highly influence the toxicity of the molecule. Pyriproxyfen disrupts the development of numerous species and adversely impacts various physiological events. It can also disturb the behavior of the organisms such as their predatory and swimming performances. Although some experimental studies focus on the environmental fate of pyriproxyfen metabolites, those dealing with their aquatic ecotoxicity assessment are scarce. In the same way, the limited number of studies dealing with the search of pyriproxyfen residues in lake, river, and other natural aquatic media does not include the identification of the metabolites.

Low concentration of 2,4,6-tribromophenol (TBP) represents a risk to South American silver catfish Ramdia quelen (Quoy and Gaimard, 1824) population

The 2,4,6-tribromophenol (TBP) is an environmental persistent pollutant widely used as flame retardant, antimicrobial and insecticide agent in wood preservation and plastic production. Currently, TBP is found in environmental compartments such as soil, freshwater, groundwater, sewage sludge and domestic dust, but the effects to biota and the risk of exposure to aquatic vertebrates are still scarce. In the present study, Rhamdia quelen fish embryos (8 h post-fertilization - hpf) were exposed to 0.3 and 3.0 μg L^-1 of TBP until 96 hpf. Biochemical biomarkers, hatching, survival and larvae/embryo malformations were evaluated after exposure. Additionally, a mathematical model was proposed to evaluate the effects along further generations. The results showed that TBP decreased the survival level but did not cause significant difference in the hatching rates. After 72 and 96 hpf, individuals from the highest tested concentration group showed more severe malformations than individuals from control and the lower concentrations groups. The deformities were concentrated on the embryos facial region where the sensorial structures related to fish behavior are present. The biochemical biomarkers revealed both oxidative stress and neurotoxicity signs after exposure to the contaminant, while the application of the mathematical model showed a decrease of population in both tested TBP concentrations. In conclusion, the current results demonstrated that TBP is toxic to R. quelen embryos and represents a risk to population after early life stage exposure.

Nociceptive-like behavior and analgesia in silver catfish (Rhamdia quelen)

Fish are useful animal models in research and have been employed in developing new pharmacological approaches. This study aimed to establish the use of silver catfish (Rhamdia quelen) as an animal model to evaluate antinociceptive activity. Initially, different concentrations of acetic acid (2.5-20%), formalin 1% (1-10 μL), menthol 0.5% (1-10 μL) or vehicle were injected in the lips to establish which concentration of each sample promotes nociceptive-like behavior in various parameters. The effect of morphine (0.5-10 mg/kg) on locomotion parameters was also evaluated for antinociceptive concentration determination. Morphine was administered intramuscularly immediately prior to algogen administration. The inhibition was evaluated with the antagonist naloxone (5 mg/kg), which was administered in the same way. Recording time varied according to the algogen used in each test and locomotor activity was evaluated by ANY-maze® software. Acid acetic at 15%, 10 μL of 1% formalin, and 1 μL of 0.5% menthol were chosen since they promoted nociceptive-like behavior in several parameters. Morphine (5 mg/kg) reversed the algogen-induced nociceptive-like behavior and naloxone inhibited this effect. Therefore, the proposed experimental model demonstrated specificity for nociception, since the reversion of the nociceptive-like behavior for a compound with well-described analgesic activity was observed. This new pharmacological model contributes to evaluating compounds with analgesic potential and developing new analgesic drugs, in addition to being a promising alternative to use with rodents.