Bioconcentration and toxicological impacts of fipronil and 2,4-D commercial formulations (single and in mixture) in the tropical fish, Danio rerio

The insecticide fipronil and the herbicide 2,4-D are the most applied pesticides in sugarcane crops leading to aquatic contamination. The whole-body bioconcentration of fipronil and 2,4-D, single and in mixture, was evaluated in Danio rerio after 96-h exposure. The activities of catalase (CAT) and glutathione S-transferase(GST) in whole body and in the gills and the acetylcholinesterase (AChE) in muscle were determined. The gill histopathology and the morphology of the pavement (PVC) and the mitochondria-rich(MRC) cells at gill surface were analyzed. Bioconcentration occurred after exposure to fipronil (2.69 L kg^-1) and 2,4-D (1.73 L kg^-1) single and in mixture of fipronil (3.10 L kg^-1) and 2,4-D (1.27 L kg^-1). Whole-body CAT activity was unchanged, and its activity decreased in the gills after exposure to fipronil and increased after exposure to 2,4-D and mixture. GST and AChE increased after single exposure to each pesticide and mixture of both. Fish exposed to mixture increased the MRC fractional area (MRCFA) which suggested possible ionic regulation disturbance and reduced the microridge of the PVC surface. Synergistic interactions occurred in the CAT activity and MRCFA after exposure to mixture of pesticides. The results indicate that the recommended application dose of fipronil and 2,4-D, single or in mixture, for sugarcane crops affects this fish species altering its homeostasis.

Whole-body bioconcentration and biochemical and morphological responses of gills of the neotropical fish Prochilodus lineatus exposed to 2,4-dichlorophenoxyacetic acid or fipronil individually or in a mixture

The herbicide 2,4-dichlorophenoxyacetic acid (2,4-D) and the insecticide fipronil have been used widely in agriculture and detected in aquatic ecosystems, where they threaten wildlife. This study evaluated the whole-body bioconcentration and the biochemical and morphological changes in the gills of the neotropical fish Prochilodus lineatus exposed for 96 h to 2,4-D or fipronil as single compounds or as a mixture (2,4-D + fipronil). Fish exposed to either compound alone bioconcentrated 2,4-D (77 ± 23 ng g ^- 1 fish dry mass) and fipronil (789 ± 178 ng g ^- 1 fish dry mass). Fish exposed to 2,4-D + fipronil bioconcentrated fipronil (683 ± 73 ng g ^- 1 fish dry mass) but not 2,4-D. In the gills, catalase (CAT) and glutathione-S-transferase (GST) activities and the lipid peroxidation (LPO) level increased after exposure to 2,4-D. GST activity increased after exposure to fipronil. Conversely, no changes occurred in CAT and GST activities and LPO upon exposure to 2,4-D + fipronil. Histopathological changes such as hyperplasia, cellular hypertrophy, epithelial lifting, and vascular congestion were frequent in the gills of fish exposed to 2,4-D or fipronil individually or 2,4-D + fipronil. The mitochondria-rich cell (MRC) density increased on gill surface in fish exposed to fipronil or 2,4-D + fipronil. Only exposure to 2,4-D alone induced oxidative stress in the gills. Most morphological changes showed defense responses against the pesticides; however, hypertrophy and the change in MRC indicated compensatory responses to maintain the gill osmoregulatory function. The 2,4-D + fipronil mixture showed antagonistic interaction, except for the MRC fractional area at gill surface, which showed synergistic interaction. This is the first report showing antagonistic interaction of 2,4-D and fipronil in the gills after exposing fish to the mixture of both pesticides. The biochemical and morphological changes in gills endanger the gill functions, a phenomenon that implies an energy cost for fish.

Environmentally-induced osmoregulation in Neotropical freshwater stingrays (Myliobatiformes: Potamotrygoninae) after controlling for phylogeny

The osmotic physiology of freshwater stingrays was investigated in fifteen species from white (WW), black (BW), and clearwater (CW) rivers of Brazilian hydrographic basins. Regardless of phylogeny, potamotrygonids collected in the BW (Negro, Jutai, Nhamunda, and Manacapuru rivers), and CW (Tapajos, Parana, Mutum, Demeni, and Branco rivers) exhibited lower levels of osmolytes and plasma osmolality than those from WW (Amazon estuary, Solimoes, and Tarauaca rivers). However, the gill and kidney Na⁺/K⁺-ATPase activities were higher in the potamotrygonid species from BW and CW than those from WW. These results may be related to the ability of the potamotrygonids to achieve high ion uptake from ion-poor waters, such as those of BW and/or CW. Additionally, the high kidney Na⁺/K⁺-ATPase activity may help to minimize ion loss and generate diluted urine. Thus, diffusional losses of salts are balanced by uptake of ions in the gill, and reabsorption by the kidney. The physiological traits showed a weak phylogenetic signal, which indicates a strong evolutionary convergence. Multivariate analyses revealed that variations in physiological traits has a significant association with the type of water, as well as its physical and chemical characteristics such as electric conductivity and pH. Therefore, the South American Neotropical freshwater stingrays adjust their osmoregulatory mechanisms according to the environment in which they live.

Biochemical and morphological biomarker responses in the gills of a Neotropical fish exposed to a new flavonoid metal-insecticide

The flavonoid metal-insecticide [Mg(hesp)₂(phen)], denominated MgHP, has high potential for controlling agricultural pests. If applied in large scale, it may reach aquatic ecosystems and be harmful to the biota. This study evaluated the effects of MgHP in the gills of the Neotropical fish, Prochilodus lineatus by determining the activity of superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx) and glutathione s-transferase (GST), and the levels of glutathione (GSH) and lipid peroxidation (LPO) after 24 and 96 h exposure to 0, 1, 10, 100 and 1000 μg L^-1. The histopathological changes with emphases to mitochondria-rich cells (MRC) were evaluated as well. After 24 h exposure the enzyme activities and the GSH and LPO levels were unchanged however, after 96 h exposure to high MgHP concentration (1000 μg L^-1), the GST activity and GSH levels increased. Oxidative stress measured as LPO levels did not occur after MgHP exposure in both periods. Gill tissue alterations increased after MgHP exposure to 10, 100 and 1000 μg L^-1. Cellular atrophy, pillar cells changes, filament epithelium hyperplasia and hypertrophy, lamellar epithelium hyperplasia were the most frequent histopathology. MRC in the filament epithelium decreased after exposure to 24 h and increased after 96 h indicating possible transitory osmo-ionic disruption. P. lineatus exhibited high tolerance to MgHP. The increased GST activity and GSH levels after 96 h exposure suggested possible MgHP accumulation and concentration- and time-dependent response. Histopathology in the gills of exposed fish occurred at high MgHP concentrations. These results suggested that the MgHP into water, at high concentrations, affect the gills by changing GST activity, GSH levels and histology being useful biomarkers for MgHP water contamination.

Histological and molecular changes in gill and liver of fish (Astyanax lacustris Lütken, 1875) exposed to water from the Doce basin after the rupture of a mining tailings dam in Mariana, MG, Brazil

The effects of the rupture of a mining tailings dam were investigated using the gills and liver of Astyanax lacustris as a proxy for environmental quality. The fish were exposed for seven days to water sampled forming four groups: upstream of the dam rupture (P1), and 22 km (P2); 48 km (P3); and 70 km (P4) downstream from the dam rupture in the Doce River basin. The control group received dechlorinated tap water. The dissolved concentrations of metals were determined by Inductively Coupled Plasma Mass Spectrometry (ICP-MS). We evaluated the histology of the gills and liver, as well as, immunohistochemistry for HSP70 and Na⁺/K⁺ ATPase (NKA) in the gills, and for P-gp in liver. In all sites we observed a mix of metals, with higher concentrations of Mn, Cd, As, and Cu/Cr in P1, P2, P3, and P4, respectively. All treatments groups showed histological changes in gills and liver, with the highest amount of these alterations found in the P2 group. Disorganization of the secondary lamellae, epithelial lifting, and mitochondria-rich cells (MRC) were observed in the gills. The parenchyma of the liver was rather disorganized, and hepatocytes and nuclei showed hypertrophy, vacuolization and cytoplasmic degeneration. A higher immunoreaction of HSP70 in P2 when compared with the other groups and lower labeling of HSP70 in the P4 was registered. In P2 and P3, NKA-positive cells were observed with hypertrophy and disorganization. Morphometric analyses of the liver revealed that all treatment groups presented a lower immunolabeling of P-gp when compared with the control group. Thus, the experimental approach revealed that the water from Doce basin can promote histological alterations in fish's liver and gills, as well as modulation of disruption of ionic balance, cellular responses to stress, and cell detoxification pathways.

Osmoregulatory disturbance in Neotropical fish exposed to the crude extracts of the cyanobacterium, Radiocystis fernandoi

Blooms of cyanobacteria, a common event in eutrophic environments, result in the release of potentially toxic substances into the water. The cyanobacterium Radiocystis fernandoi produces microcystin (MC) and other peptides that may disturb homeostasis. This study evaluated the effect of intraperitoneal injections containing the crude extract (CE) of R. fernandoi strain R28 on the gills and kidneys of neotropical fish, Piaractus mesopotamicus, 3, 6 and 24 h post-injection. CE contained MC-RR, MC-YR and minor other oligopeptides. Plasma ions and the activities of the enzymes PP1 and PP2A, Na⁺/K⁺-ATPase (NKA), H⁺-ATPase (HA) and carbonic anhydrase (CA) were determined and morphological changes in both the gills and kidneys were characterized. Compared to controls, the concentration of Na⁺ within the plasma of P. mesopotamicus decreased after treatment with CE 3 h post treatment and increased after 24 h; the concentration of K⁺ decreased after 6 h. The activity of the endogenous PP1 and PP2A was unchanged in the gills and was inhibited in the kidneys 6 h after i.p. injection. In the gills, NKA activity increased after 3 h and decreased 6 h post i.p. exposure. Further, NKA activity did not differ from the controls 24-h post injection. In the kidneys, NKA, HA and CA activities were unaffected by treatment. The mitochondria-rich cell (MRC) density in the gills decreased after 3 h in the filament and 3 and 6 h in the lamellae and was restored to the control levels 24 h post-exposure. Filament epithelial hyperplasia and hypertrophy, lamellar atrophy and rupture of the lamellar epithelium were the most common effects of treatment in the gills. No histopathological changes occurred in the kidneys. This study demonstrates that a single dose of toxic CE from R. fernandoi can cause a transitory ion imbalance in P. mesopotamicus which is related to the changes in MRC levels and NKA activity. Ionic balance was recovered 24 h post i.p. injection, however, morphological changes that occurred in the gills took a longer amount of time to return to normal. To conclude, the effects of components contained within the CE of R. fernandoi may be harmful to P. mesopotamicus. In particular, the recovery of ionic regulation depends on MRC responses and histopathological changes produced by CE may affect gas exchange and other gill functions.

Functional and evolutionary perspectives on gill structures of an obligate air-breathing, aquatic snail

Ampullariids are freshwater gastropods bearing a gill and a lung, thus showing different degrees of amphibiousness. In particular, Pomacea canaliculata (Caenogastropoda, Ampullariidae) is an obligate air-breather that relies mainly or solely on the lung for dwelling in poorly oxygenated water, for avoiding predators, while burying in the mud during aestivation, and for oviposition above water level. In this paper, we studied the morphological peculiarities of the gill in this species. We found (1) the gill and lung vasculature and innervation are intimately related, allowing alternation between water and air respiration; (2) the gill epithelium has features typical of a transporting rather than a respiratory epithelium; and (3) the gill has resident granulocytes within intraepithelial spaces that may serve a role for immune defence. Thus, the role in oxygen uptake may be less significant than the roles in ionic/osmotic regulation and immunity. Also, our results provide a morphological background to understand the dependence on aerial respiration of Pomacea canaliculata. Finally, we consider these findings from a functional perspective in the light of the evolution of amphibiousness in the Ampullariidae, and discuss that master regulators may explain the phenotypic convergence of gill structures amongst this molluscan species and those in other phyla.

Immunolocalization of calcium sensing and transport proteins in the murine endolymphatic sac indicates calciostatic functions within the inner ear

An exceptionally low calcium (Ca²⁺) concentration in the inner ear endolymph ([Ca²⁺]_endolymph) is crucial for proper auditory and vestibular function. The endolymphatic sac (ES) is believed to critically contribute to the maintenance of this low [Ca²⁺]_endolymph. Here, we investigated the immunohistochemical localization of proteins that are presumably involved in the sensing and transport of extracellular Ca²⁺ in the murine ES epithelium. Light microscopic and fluorescence immunolabeling in paraffin-embedded murine ES tissue sections (male C57BL/6 mice, 6–8 weeks old) demonstrated the presence of the calcium-sensing receptor CaSR, transient receptor potential cation channel subtypes TRPV5 and TRPV6, sarco/endoplasmic reticulum Ca²⁺-ATPases SERCA1 and SERCA2, Na⁺/Ca²⁺ exchanger NCX2, and plasma membrane Ca²⁺ ATPases PMCA1 and PMCA4 in ES epithelial cells. These proteins exhibited (i) membranous (apical or basolateral) or cytoplasmic localization patterns, (ii) a proximal-to-distal labeling gradient within the ES, and (iii) different distribution patterns among ES epithelial cell types (mitochondria-rich cells (MRCs) and ribosome-rich cells (RRCs)). Notably, in the inner ear membranous labyrinth, CaSR was exclusively localized in MRCs, suggesting a unique role of the ES epithelium in CaSR-mediated sensing and control of [Ca²⁺]_endolymph. Structural loss of the distal ES, which is consistently observed in Meniere’s disease, may therefore critically disturb [Ca²⁺]_endolymph and contribute to the pathogenesis of Meniere’s disease.

Ion transport its regulation in the endolymphatic sac: suggestions for clinical aspects of Meniere's disease

Ion transport and its regulation in the endolymphatic sac (ES) are reviewed on the basis of recent lines of evidence. The morphological and physiological findings demonstrate that epithelial cells in the intermediate portion of the ES are more functional in ion transport than those in the other portions. Several ion channels, ion transporters, ion exchangers, and so on have been reported to be present in epithelial cells of ES intermediate portion. An imaging study has shown that mitochondria-rich cells in the ES intermediate portion have a higher activity of Na⁺, K⁺-ATPase and a higher Na⁺ permeability than other type of cells, implying that molecules related to Na⁺ transport, such as epithelial sodium channel (ENaC), Na⁺–K⁺–2Cl⁻ cotransporter 2 (NKCC2) and thiazide-sensitive Na⁺–Cl⁻ cotransporter (NCC), may be present in mitochondria-rich cells. Accumulated lines of evidence suggests that Na⁺ transport is most important in the ES, and that mitochondria-rich cells play crucial roles in Na⁺ transport in the ES. Several lines of evidence support the hypothesis that aldosterone may regulate Na⁺ transport in ES, resulting in endolymph volume regulation. The presence of molecules related to acid/base transport, such as H⁺-ATPase, Na⁺–H⁺ exchanger (NHE), pendrin (SLC26A4), Cl⁻–HCO₃⁻ exchanger (SLC4A2), and carbonic anhydrase in ES epithelial cells, suggests that acid/base transport is another important one in the ES. Recent basic and clinical studies suggest that aldosterone may be involved in the effect of salt-reduced diet treatment in Meniere’s disease.

Development of gas exchange and ion regulation in two species of air-breathing fish, Betta splendens and Macropodus opercularis

Aquatic air-breathing anabantoids, a group of fish species characterized by the presence of a labyrinth organ and some gills, exhibit morphological variations. This study aimed to examine whether unequal gill growth begins during the early stages and described the sequence of the early gill developmental events in Betta splendens and Macropodus opercularis. To determine when the ion regulatory and gas exchange abilities first appear in the gills, mitochondria-rich cells (MRCs) and neuroepithelial cells (NECs) were examined in young B. splendens. To evaluate the relative importance of the gills and the labyrinth organ under different levels of oxygen uptake stress, the levels of carbonic anhydrase II (CAII) and Na(+)/K(+)-ATPase (NKA) protein expressions in 2 gills and the labyrinth organ were examined in M. opercularis. We found that the first 3 gills developed earlier than the 4th gill in both species, an indication that the morphological variation begins early in life. In B. splendens, the MRCs and NECs clearly appeared in the first 3 gills at 4 dph and were first found in the 4th gill until 11 dph. The oxygen-sensing ability of the gills was concordant with the ionoregulatory function. In M. opercularis, the hypoxic group had a significantly higher air-breathing frequency. CAII protein expression was higher in the labyrinth organ in the hypoxic group. The gills exhibited increased NKA protein expression in the hypoxic and restricted groups, respectively. Functional plasticity in CAII and NKA protein expressions was found between the gills and the labyrinth organ in adult M. opercularis.

Effects of salinity on metabolic rate and branchial expression of genes involved in ion transport and metabolism in Mozambique tilapia (Oreochromis mossambicus)

This study investigated the effects of two rearing salinities, and acute salinity transfer, on the energetic costs of osmoregulation and the expression of metabolic and osmoregulatory genes in the gill of Mozambique tilapia. Using automated, intermittent-flow respirometry, measured standard metabolic rates (SMRs) of tilapia reared in seawater (SW, 130 mg O₂ kg⁻¹ h⁻¹) were greater than those reared in fresh water (FW, 103 mg O₂ kg⁻¹ h⁻¹), when normalized to a common mass of 0.05 kg and at 25±1°C. Transfer from FW to 75% SW increased SMR within 18h, to levels similar to SW-reared fish, while transfer from SW to FW decreased SMR to levels similar to FW-reared fish. Branchial gene expression of Na⁺-K⁺-2Cl⁻ cotransporter (NKCC), an indicator of SW-type mitochondria-rich (MR) cells, was positively correlated with SMR, while Na⁺-Cl⁻ cotransporter (NCC), an indicator of FW-type MR cells, was negatively correlated. Principal Components Analysis also revealed that branchial expression of cytochrome c oxidase subunit IV (COX-IV), glycogen phosphorylase (GP), and a putative mitochondrial biogenesis regulator in fish, peroxisome proliferator-activated receptor γ coactivator 1α (PGC-1α), were correlated with a higher SMR, plasma osmolality, and environmental salinity, while expression of glycogen synthase (GS), PGC-1β, and nuclear respiratory factor 1 (NRF-1) had negative correlations. These results suggest that the energetic costs of osmoregulation are higher in SW than in FW, which may be related to the salinity-dependent differences in osmoregulatory mechanisms found in the gills of Mozambique tilapia.