Gill Respiration Research Articles

Histopathological assessment of Atlantic salmon exposed to calcium oxide particles: a controlled clinical study

Particulate calcium oxide (CaO) has been successfully used for the control of sea urchin and starfish populations. Recent studies have proven its efficacy in killing planktonic copepods, making it a promising and cheap option for salmon louse control in the Atlantic salmon (Salmo salar) farming industry. Additionally, preliminary laboratory tests demonstrated that exposure to 0.2 g/L–0.6 g/L of fine CaO particles induced significant mortality of salmon louse (Lepeophtheirus salmonis) in the planktonic stages. The present study investigated the effects of water treatment with fine CaO particles [0.2 g/L or 127.4 g/m2; 0.1 mm–0.3 mm], conducted twice a week for three consecutive weeks at 5°C and 12°C on Atlantic salmon post-smolt in a flow-through system. The study compared mortality rates and histopathology of skin, eyes, gills, and intestines between treated and untreated control salmon. The results indicated that CaO exposure did not induce fish mortality or histopathological damages in the skin, eyes, or intestines. Although there were no significant effects of CaO exposure on gill inflammation or hyperplasia, the exposure did increase the occurrence of gill vascular injuries and necrosis in small portions of the tissue (< 10% of the respiratory gill tissue in most of the samples) by 60% and 35%, respectively. The effect was not modulated by temperature or time. The results indicate that the CaO treatment protocol used in this study is not lethal to Atlantic salmon and is safe for most analyzed tissues. Nonetheless, the induction of vascular damage and necrosis in the gill, albeit in small tissue portions, emphasizes the need for further research. It is crucial to develop a protocol that avoids such lesions, ensuring the secure application of CaO as an antiparasitic treatment in salmon aquaculture.

Neurotoxic pesticides change respiratory parameters in early gill-breathing, but not in skin-breathing life-stages of zebrafish (Danio rerio)

Neurotoxic compounds can interfere with active gill ventilation in fish, which might lead to premature death in adult fish, but not in skin-breathing embryos of zebrafish, since these exclusively rely on passive diffusion across the skin. Regarding lethality, this respiratory failure syndrome (RFS) has been discussed as one of the main reasons for the higher sensitivity of adult fish in the acute fish toxicity test (AFT), if compared to embryos in the fish embryo toxicity test (FET). To further elucidate the relationship between the onset of gill respiration and death by a neurotoxic mode of action, a comparative study into oxygen consumption (MO2), breathing frequency (fv) and amplitude (fampl) was performed with 4 d old skin-breathing and 12 d old early gill-breathing zebrafish. Neurotoxic model substances with an LC50 FET/AFT ratio of > 10 were used: chlorpyrifos, permethrin, aldicarb, ziram, and fluoxetine. Exposure to hypoxia served as a positive control, whereas aniline was tested as an example of a narcotic substance interfering non-specifically with gill membranes. In 12 d old larvae, all substances caused an increase in MO2, fv and partly fampl, whereas effects were minor in 4 d old embryos. An increase of fv in 4 d old embryos following exposure to chlorpyrifos, aldicarb and hypoxia could not be correlated with an increased MO2 and might be attributed either to (1) to the successfully postponed decrease of arterial partial pressure of oxygen (PO2) through support of skin respiration by increased fv, (2) to an unspecific stimulation of the sphincter muscles at the base of the gill filaments, or (3) to the establishment of oxygen sensing for later stages. In gill-breathing 12 d old zebrafish, a concentration-dependent increase of fv was detected for aniline and chlorpyrifos, whereas for aldicarb, fluoxetine and permethrin, a decline of fv at higher substance concentrations was measured, most likely due to the onset of paralysis and/or fatigue of the gill filament sphincter muscles. Since alterations of fv serve to postpone the decrease in arterial PO2 and MO2 increased with decreasing fv, the respiratory failure syndrome could clearly be demonstrated in 12 d old zebrafish larvae. Passive respiration across the skin in zebrafish embryos could thus be confirmed as a probable reason for the lower sensitivity of early life-stages to neurotoxicants. Integration of respiratory markers into existing testing protocols with non-protected developmental stages such as embryos might help to not underestimate the toxicity of early life-stages of fish.

Slippery hydrogel surface on PTFE hollow fiber membranes for sustainable emulsion separation.

Establishing an efficient and sustainable membrane module is of great significance for practical oil/water emulsion separation. Superwetting membranes have been extensively studied but cannot meet long lasting separation owing to inevitable membrane fouling. Herein, we constructed a hydrogel-mediated slippery surface on polytetrafluoroethylene (PTFE) hollow fibers and then designed a flexible and swing hollow fiber membrane module inspired by fish gill respiration, which achieved sustainable emulsion separation. A vinyl silane-crosslinked polyvinylpyrrolidone (PVP) hydrogel was interpenetrated with nano-fibrils of the PTFE hollow fibers, thus facilitating fast water permeance while resisting oil intrusion. Liquid-like polydimethylsiloxane (PDMS) brushes were then grafted to promote oil aggregation-release from the membrane surface. Owing to the heterogeneous surface and gill-like structure, the designed PTFE hollow fiber membrane module could separate emulsion in a long-term filtration process, maintaining a high water permeability of 500 L m-2 h-1 bar-1 with a separation efficiency of over 99.9% for 5000 min. This novel technique shows its great potential to realize practical emulsion separation by solving the persistent problem of membrane fouling and permeance decay.

Suppression of hydrofoil unsteady cavitation by periodic jets based on fish gill respiration

Cavitation is a phase change phenomenon that occurs between the liquid and vapour phases inside a homogeneous liquid or at the interface between a solid and a liquid, and the generation, collapse and shedding of cavitation are the sources of undesirable characteristics of fluid machinery. A periodic jet scheme based on the principle of bionics is designed and applied to a Clark-Y hydrofoil with a chord length of 70 mm to suppress the cavitation of fluid machinery under high-speed flow conditions. Different schemes are numerically simulated using large eddy simulation combined with the Zwart–Gerber–Belamri cavitation model to numerically simulate the different schemes. The results show that adding periodic jet to the hydrofoil can reduce the cavitation of the hydrofoil without losing the lift resistance of the hydrofoil, and the cavitation volume is 47%–52% of the original hydrofoil.

Allometric Growth Patterns and Ontogenetic Development during Early Larval Stages of Schizothorax waltoni Regan and Percocypris retrodorslis in Southwest China

Due to a sharp decline in resources, Schizothorax waltoni Regan and Percocypris retrodorslis have been listed as wildlife under second-class protection in China. Under culture conditions, the early development and allometric growth patterns of S. waltoni and P. retrodorslis were researched from the hatching stage to 60 DPHs (days post-hatching), and a sampling of ten to fifteen larvae was made every day, followed by measurements with Axio Vision 4.8 software (Carl Zeiss AG, Jena, Germany). Morphological indicators included the anal fin length, the body depth, the body depth at the anus level, the caudal fin length, the dorsal fin length, the eye diameter, the head length, the head depth, the pectoral fin length, the tail length, the trunk length, the snout length, the total length, and the ventral fin length. Based on the morphology development of S. waltoni Regan and P. retrodorslis, four periods of larval growth were identified: pre-flexion larvae at 0–14 DPHs and 0–16 DPHs; flexion larvae at 14–23 DPHs and 16–26 DPHs, post-flexion larvae at 23–50 DPHs and 26–52 DPHs, and the juvenile stage. In newly hatched larvae, most organs and body parts were not differentiated, and they successively developed within 26 DPHs. The depletion of the yolk sac was observed at 23 DPHs and 25 DPHs. Allometric growth mainly occurs in the head and tail regions, indicating that body parts related to feeding and swimming behaviors were more important than the other parts. In addition, the growth pattern shows that the development of organs gives priority to the functions of gill respiration, sensation, exogenous feeding, and swimming. The inflection points of body part growth patterns only appeared before 40 DAH, so future studies should concentrate focus on developing the best feeding from the first feeding to 40 DAH. These outcomes were discussed with regard to the ontogeny of the functional morphology in relation to ecology and aquaculture. It is expected that this research can provide valuable perspectives in species conservation.

Functional threshold responses of benthic macroinvertebrates to environmental stressors in reservoirs

Reservoirs are aquatic ecosystems created by humans to supply water needs. They can impair aquatic diversity due to the lack of connectivity, reduced water volume, and pressures exerted by surrounding human activities. These changes are expected to produce abrupt fluctuations in the reservoirs' environment, thus influencing the structure and functioning of aquatic communities. Therefore, this study aimed to understand the impact of a range of environmental stressors in reservoirs on benthic macroinvertebrates by analyzing their functional threshold response. Biological data were collected in six reservoirs from the semi-arid region of Northeast Brazil, as case study. A total of 37.874 benthic macroinvertebrates belonging to 35 taxa were collected. Nevertheless, almost 90% of this abundance belonged to three species alone, considered generalists, with multivoltine reproduction and from the gatherer-collectors feeding group. Increases in environmental stressors such as salinity, nitrate, ammonia, and dissolved solids led to the selection of macroinvertebrates with specific traits (e.g., protected body, gill respiration, and large body size). These functional traits showed differences in their threshold response depending on the stressors and are indicators of the effects of these stressors on the reservoirs. Some of the potential sensitive traits (with a negative threshold response to the stressor) could also associate with other stressors, demonstrating that tolerance of benthic macroinvertebrates is defined by a set of functional characteristics. Overall, the increase in stressor’ gradients selected functionally tolerant organisms with high resistance capacity, but these were represented by dominant species. This resulted in low diversity in the reservoirs, which may compromise ecosystem functioning, and raises concerns about adequate management of the systems.

Disclosing the bioaccumulation and biomagnification behaviors of emerging per/polyfluoroalkyl substances in aquatic food web based on field investigation and model simulation

Emerging poly/perfluoroalkyl substances (PFASs) have been widely detected in the environment, but their bioaccumulation and biomagnification behaviors are not well understood. We collected surface water, sediment, and various aquatic organisms from Lake Taihu, China. Several emerging PFASs, such as fluorotelomer sulfonates (FTSs), hexafluoropropylene oxides (HFPOs), and chlorinated polyfluoroalkyl ether sulfonic acids (Cl-PFESAs) were frequently detected in water and sediment samples. The concentrations of HFPO trimer acid (HFPO-TA), 4,8-dioxa-3 H-per-fluorononanoate, and FTSs were remarkably higher than those reported previously, indicating that their application is increasing in Taihu Basin. These emerging PFASs displayed higher sediment/water partitioning coefficients (log Koc) than the corresponding perfluoroalkyl acids (PFAAs) with the same perfluorinated carbon chain length. HFPOs and Cl-PFESAs were more labile to deposit in fish livers than perfluorooctanoic and perfluorooctane sulfonic acids, respectively. Both field investigations and model simulations indicated that HFPO-TA and Cl-PFESAs, as well as the hydrogen-substituted analogs of 6:2 Cl-PFESA (6:2 H-PFESA), were biomagnified along the aquatic food chain. The bioaccumulation model simulation revealed that the accumulation of these emerging PFASs in fish was mainly through dietary intake, whereas gill respiration and fecal excretion facilitated their elimination. Metabolic transformation might also contribute to their elimination relative to the legacy ones.

The onset of active gill respiration in post-embryonic zebrafish (Danio rerio) larvae triggers an increased sensitivity to neurotoxic compounds.

Originally designed as a general alternative to acute fish toxicity testing (AFT), the fish embryo toxicity test (FET) has become subject to concerns with respect to neurotoxic substances. Whereas oxygen uptake in the fish embryo primarily occurs via diffusion across the skin, juvenile and adult fish rely on active ventilation of the gills. As a consequence, substances including, e.g., neurotoxicants which prevent appropriate ventilation of gills ("respiratory failure syndrome") might lead to suffocation in juvenile and adult fish, but not in skin-breathing embryos. To investigate if this respiratory failure syndrome might play a role for the higher sensitivity of juvenile and adult fish to neurotoxicants, a modified acute toxicity test using post-embryonic, early gill-breathing life-stages of zebrafish was developed with chlorpyrifos, permethrin, lindane, aldicarb, ziram and aniline as test substances. Additionally, a comparative study into bioaccumulation of lipophilic substances with logKow > 3.5 and swimbladder deflation as potential side effects of the respiratory failure syndrome was performed with 4 d old skin-breathing and 12 d old gill-breathing zebrafish. With respect to acute toxicity, post-embryonic 12 d larvae proved to be more sensitive than both embryos (FET) and adult zebrafish (AFT) to all test substances except for permethrin. Accumulation of chlorpyrifos, lindane and permethrin was 1.3- to 5-fold higher in 4 d old than in 12 d old zebrafish, suggesting that (intermediate) storage of substances in the yolk might reduce bioavailability and prevent metabolization, which could be a further reason for lower toxicity in 4 d than in 12 d old zebrafish. Whereas ziram and aniline showed no significant effect on the swimbladder, zebrafish exposed to chlorpyrifos, lindane and permethrin showed significantly deflated swimbladders in 12 d old larvae; in the case of aldicarb, there was a significant hyperinflation in 4 d old larvae. Swimbladder deflation in post-embryonic 12 d zebrafish larvae might be hypothesized as a reason for a lack of internal oxygen supplies during the respiratory failure syndrome, whereas in 4 d old embryos cholinergic hyperinflation of the swimbladder dominates over other effects. Regarding acute lethality, the study provides further evidence that the switch from transcutaneous to branchial respiration in post-embryonic zebrafish life-stages might be the reason for the higher sensitivity of juvenile and adult fish to neurotoxic substances.

Simulation modelling the structure related bioaccumulation and biomagnification of per- and polyfluoroalkyl substances in aquatic food web

Until now, there is no bioaccumulation model to predict bioaccumulation of polyfluoroalkyl substances (PFASs) in aquatic organisms due to their unique amphiphilic properties. For the first time, protein contents instead of lipid contents of organisms were used in bioaccumulation models to predict the concentrations and reveal the accumulation mechanisms of PFASs in various aquatic organisms, based on the available data. Comparison between the modeled and measured results indicated the models were promising to predict the PFAS concentrations in the fishes at different trophic levels very well, as well as their bioaccumulation factors (BAF) and trophic magnification factors (TMF) of PFASs in fish. Both water and sediment are important exposure sources of PFASs in aquatic organisms. As the two main uptake pathways, the contribution of gill respiratory decreases while that of dietary intake increases with the chain length of PFASs increasing. Fecal excretion and gill respiration are the main pathways for fish to eliminate PFASs, and their relative contributions increase and decrease respectively with chain length. The short-chain (C6–C8) perfluoroalkyl acids (PFAAs) are greatly eliminated via gill respiratory quickly, leading to their very low BAFs. As the carbon chain length increases, dietary intake becomes dominant in the uptake, while elimination is mainly through fecal excretion with relatively low rates, especially in the fishes with high protein contents. For the very long chain (C12–C16) PFASs, they are very difficult to excrete with a low total elimination rate constant (ke = 0.463–0.743 d−1), thus leading to their high BAFs and TMFs. The high intake rate but low elimination rate, as well as the high water and sediment concentrations together contribute to the highest accumulated concentration perfluorooctane sulfonic acid in the fish of Taihu Lake.

A novel fish behavior: “Floating” of Paramisgurnus dabryanus loaches

Unusual behavior has been noted in Paramisgurnus dabryanus loaches, which have been seen to float on the water, both on aquafarms and laboratories. Animal behavior usually reflects adaptation to the environment, but this “floating” behavior undoubtedly increases the risk of being predated. In order to understand the ecological significance, we first studied the basic characteristics of this behavior. The floating loaches showed five typical characteristics: (1) They floated more at night than during the day, (2) They mainly floated for a short time (< 30 s), (3) The gill respiration frequency decreased significantly (P < 0.05), (4) The proportion of floating fish gradually increased with water temperature (P < 0.05), (5) Juvenile P.dabryanus floated for the first time approximately 14 dph, which coincided with the period when the intestine tract penetrated through and they began to breathe with it.

Functional responses of Odonata larvae to human disturbances in neotropical savanna headwater streams

Headwater streams are facing increasing disturbances from human pressures worldwide, thus better knowledge about bioindicators, particularly aquatic insect responses to various pressures and stressors, are urgently needed. Multiple trait-based approaches consider species attributes filtered by the environment, allowing them to persist in ecosystems under environmental pressures. Because this approach has been minimally explored in Odonata larvae, we aimed to understand how anthropogenic stressors structure Odonata larval assemblages in neotropical savanna streams by using multiple trait-based approaches. We hypothesized that a set of stressors--such as reduced substrate heterogeneity, poor water quality, natural land cover converted to pasture and agriculture, and reduced local riparian canopy cover--select Odonata functional traits. We collected 3209 Odonata larvae from 186 neotropical savanna headwater stream sites and used 39 environmental variables and seven traits in 23 categories related to their functional roles in Odonata genera. To assess associations between trait categories and environmental variables, we applied RLQ and fourth-corner statistical analyses. We found strong relationships between environmental variables and sets of Odonata biological traits that were separated into two main groups. Zygoptera genera (Perilestes, Allopodagrion, Heliocharis, Argia, Epipleoneura, Mnesarete/Hetaerina, Psaironeura) have elongated body shapes, caudal lamellae respiration, conforming thermoregulation, and endophytic oviposition. Such traits favor assemblages in conditions similar to reference streams, including denser riparian vegetation, good water quality, and diverse flows and substrate. Therefore, they are more sensitive to changes in those conditions. On the other hand, Anisoptera genera (Gomphoides, Archaeogomphus, Macrothemis, Brechmorhoga, Gynothemis, Phyllocycla) have cylindrical body shapes, internal gill respiration, endothermic thermoregulation, and burrowing behavior. Those traits facilitate their survival in intermediate or disturbed stream sites, characterized by riparian deforestation, increased erosion and siltation, and higher levels of total dissolved solids and conductivity. Therefore, using Odonata larval traits can be a valuable tool for assessing and monitoring anthropogenic impacts on neotropical savanna streams.

Comparative assessment of macroinvertebrate communities within three Afromontane headwater streams influenced by different land use patterns

Headwater streams in Afromontane ecoregions harbour locally adapted aquatic communities. However, across many regions in Africa, these ecosystems and their unique aquatic biodiversity have been severely impacted by unsustainable land use practices. We tested the hypothesis that land use disturbances were the primary drivers of community dynamics by comparing spatial and temporal dynamics together with trait-environment relationships of macroinvertebrate communities in three headwater streams influenced by different land use practices. The three headwater streams were distinguished based on high conductivity, total dissolved solids and alkaline pH in the agriculture-disturbed stream, and low temperature in a stream whose riparian zone was invaded by non-native vegetation compared to a near-natural stream. Macroinvertebrate taxonomic diversity was, nevertheless, comparable among these three streams. Constrained canonical ordination revealed that seasonality was a major driver of macroinvertebrate dynamics that was reflected mostly by the abundances of six macroinvertebrate taxa (Baetis, Dicentroptelum, Afronurus, Tricorythus, Simulium and Cheumatopsyche), whereas land use contributed a small but significant difference. Trait-environment relationships reflected seasonal changes that included the importance of benthic substratum in winter, the occurrence of collector-gatherer invertebrates in spring and aerial breathing traits in summer. Land use-related traits were, nevertheless, reflected by gill respiration and grazer feeding traits represented by Afronurus in the near-natural stream, predator traits represented by Aeshna and Lestes in the invaded stream, and aerial respiration represented by Enithares, Orectogyrus and Rhagovelia in the agriculture-disturbed stream. Our results suggest that environmental variability associated with seasonality probably played a deterministic role within which land use disturbances operated. Overall, our study suggest that importance of using multiple metrics to unpack the patterns associated with land use disturbances in headwater streams.

Vapor exposure to Δ9-tetrahydrocannabinol (THC) slows locomotion of the Maine lobster (Homarus americanus)

RationaleDespite a long history of use in synaptic physiology, the lobster has been a neglected model for behavioral pharmacology. A restaurateur proposed that exposing lobster to cannabis smoke reduces anxiety and pain during the cooking process. It is unknown if lobster gill respiration in air would result in significant Δ9-tetrahydrocannabinol (THC) uptake and whether this would have any detectable behavioral effects. ObjectiveThe primary goal was to determine tissue THC levels in the lobster after exposure to THC vapor. Secondary goals were to determine if THC vapor altered locomotor behavior or nociception. MethodsTissue samples were collected (including muscle, brain and hemolymph) from Homarus americanus (N = 3 per group) following 30 or 60 min of exposure to vapor generated by an e-cigarette device using THC (100 mg/mL in a propylene glycol vehicle). Separate experiments assessed locomotor behavior and hot water nociceptive responses following THC vapor exposure. ResultsTHC vapor produced duration-related THC levels in all tissues examined. Locomotor activity was decreased (distance, speed, time-mobile) by 30 min inhalation of THC. Lobsters exhibit a temperature-dependent withdrawal response to immersion of tail, antennae or claws in warm water; this is novel evidence of thermal nociception for this species. THC exposure for 60 min had only marginal effect on nociception under the conditions assessed. ConclusionsVapor exposure of lobsters, using an e-cigarette based model, produces dose-dependent THC levels in all tissues and reduces locomotor activity. Hot water nociception was temperature dependent, but only minimal anti-nociceptive effect of THC exposure was confirmed.

Effects of different types of land-use on taxonomic and functional diversity of benthic macroinvertebrates in a subtropical river network.

Expansion of agricultural and urban areas and intensification of catchment land-use increasingly affect different facets of biodiversity in aquatic communities. However, understanding the responses of taxonomic and functional diversity to specific conversion from natural forest to agriculture and urban land-use remains limited, especially in subtropical streams where biomonitoring programs and using functional traits are still under development. Here, we conducted research in a subtropical stream network to examine the responses of macroinvertebrate taxonomic and functional diversity to different types of land-use in central China. Our results showed that medium body size, univoltine, gill respiration, and slow seasonal development were much higher in natural forest sites, while certain traits related to strong resilience and resistance (e.g., small body size, fast seasonal development, bi-or multivoltine, abundant occurrence in drift, sprawler) dominated in high-intensity agriculture and urbanization sites. We further found that land-use compromised water quality (e.g., increases in total phosphate, conductivity and water temperature) and habitat conditions (e.g., high proportion of sand and silt, gravel, and channel width) accounted for the changes in trait composition based on a combination of RLQ and fourth-corner analysis. Moreover, natural forest sites presented relatively high values of functional richness than other land-use, demonstrating the importance of natural forest maintenance to promote high levels of functional diversity. However, taxonomic diversity indexes showed higher sensitivity to distinguish different types of land-use compared to functional diversity measures. Even so, given that certain trait categories showed significant relationships with specific local environmental stressors, trait-based approaches can provide reliable evidence to diagnose the cause of impairment and complement the results of the taxonomic-based approaches. Our findings support the idea that taxonomic and functional approaches should be integrated in river restoration and land-use management.

Effect of hypoxia and air-breathing restricted on respiratory physiology of air-breathing loach (Paramisgurnus dabryanus).

This aim of this study was to determine the respiratory physiology response in the gill and gut of Paramisgurnus dabryanus under different breathing treatment patterns. The experimental design included the following three conditions: a control group without any stress treatments, an inhibited group with intestinal respiration inhibited, and an air-exposed group with gill respiration inhibited. The results indicated that the total static metabolic rate in the air-exposed group (188.92 ± 13.67 mg h-1 kg-1) was much higher than that of the other group after 7 days, decreased significantly after the first day of recovery (81.64 ± 7.85 mg h-1 kg-1). The air metabolic rate in the air-exposed group increased significantly after 7 days (P < 0.05). There was no significant difference among the groups. Histological observation on the gill and hindgut of P. dabryanus showed that the gill filament area of inhibited group became larger, while the gill structure of air exposed group showed some damage. The number of capillariesin the hindgut mucosal epithelial in air-exposed group showed a rapidly increase (P < 0.05). Likewise, the gas diffusion distance (1.24 ± 0.36 μm) became significantly shorter (P < 0.05). Lactate dehydrogenase activity of gill in the air-exposed group (846.68 ± 88.78 U mg-1 protein) significantly increased after 7 days whereas succinate dehydrogenase (1.02 ± 0.21 U mg-1 protein) and Na+/K+ ATPase (0.57 ± 0.20 U mg-1 protein) activity decreased significantly (P < 0.05). However, there was no significant change in the hindgut. After recovery, there was no significant difference in lactate dehydrogenase, succinate dehydrogenase, and Na+/K+ ATPase activity in the gill or hindgut in groups. P. dabryanus had a high viability in air-exposed condition. When recovery occurred under normoxic conditions, the physical levels of respiration returned back to the normal level quickly.

Nitric oxide mediates metabolic functions in the bivalve Arctica islandica under hypoxia.

The free radical nitric oxide (NO) is a powerful metabolic regulator in vertebrates and invertebrates. At cellular concentrations in the nanomolar range, and simultaneously reduced internal oxygen partial pressures (pO2), NO completely inhibits cytochrome-c-oxidase (CytOx) activity and hence mitochondrial- and whole-tissue respiration. The infaunal clam Arctica islandica regulates pO2 of hemolymph and mantle cavity water to mean values of <5 kPa, even in a completely oxygen-saturated environment of 21 kPa. These low internal pO2 values support a longer NO lifespan and NO accumulation in the body fluids and can thus trigger a depression of metabolic rate in the clams. Measurable amounts of NO formation were detected in hemocyte cells (~110 pmol NO 100−1 hemocytes h-1 at 6 kPa), which was not prevented in the presence of the NO synthase inhibitor L-NAME, and in the gill filaments of A. islandica. Adding a NO donor to intact gills and tissue homogenate significantly inhibited gill respiration and CytOx activity below 10 kPa. Meanwhile, the addition of the NO-oxidation product nitrite did not affect metabolic rates. The high nitrite levels found in the hemolymph of experimental mussels under anoxia do not indicate cellular NO production, but could be an indication of nitrate reduction by facultative anaerobic bacteria associated with tissue and/or hemolymph biofilms. Our results suggest that NO plays an important role in the initiation of metabolic depression during self-induced burrowing and shell closure of A. islandica. Furthermore, NO appears to reduce mitochondrial oxygen radical formation during surfacing and cellular reoxygenation after prolonged periods of hypoxia and anoxia.

The potential respiratory surfaces of a fish living in a historically polluted river

Abstract The acquisition of oxygen is fundamental for maintaining metabolic activity in fish, and most species obtain oxygen through aquatic gill respiration. Throughout evolution, different fish lineages have evolved secondary routes to obtain oxygen from atmospheric air, and the spinycheek sleeper, Eleotris pisonis, may be one example of such bimodal respiration. Gill structure and the top epithelium of the head of E. pisonis from the Subaé River (Santo Amaro, Bahia, Brazil) were evaluated morphometrically. The gills showed histopathologies, especially proliferation, which was prevalent on 35.6% of the filaments and on 13.7% of the lamellae, probably increasing the water-blood diffusion barrier of the lamellae to 5.48 ± 1.32 μm, similar to the air-blood diffusion distance of the skin (5.77 ± 1.72 μm). Quantitative morphometric analysis of histopathologies and diffusion distances could be considered as biomarkers, and also suggest the presence of cutaneous respiration as a possible strategy for aerial oxygen acquisition.

A new black fly species of the subgenus Gomphostilbia (Simulium: Simuliidae: Diptera) from India

Abstract Simulium (Gomphostilbia) agasthyamalaiense sp. nov. is described based on adults, pupae and mature larvae from a medium-flowing stream of Southern Western Ghats, India. This new species is placed in the Simulium batoense species-group of the subgenus Gomphostilbia Enderlein. This new species is characterized in the female by a scutum with three brownish-black longitudinal vittae and the hind basitarsus 5.7 times as long as wide; in the female by the large facets of upper eye with 20 vertical columns and 19 horizontal rows; in the pupa the respiratory gill with medium-long common basal stalk; and in the larva arrowhead-shaped postgenal cleft. Taxonomic notes are provided for this new species and it can be distinguished from closely related species of S. (G.) peteri. Keys are constructed to distinguish this species from ten species of the batoense species-group recorded in India. www.zoobank.org/urn:lsid:zoobank.org:pub:1D1CFEE5-A762-4F68-9EAE-9E31133146C0

Hypoxically Induced Nitric Oxide: Potential Role as a Vasodilator in Mytilus edulis Gills.

Intertidal Mytilus edulis experience rapid transgression to hypoxia when they close their valves during low tide. This induces a physiological stress response aiming to stabilize tissue perfusion against declining oxygen partial pressure in shell water. We hypothesized that nitric oxide (NO) accumulation supports blood vessel opening in hypoxia and used live imaging techniques to measure NO and superoxide anion () formation in hypoxia-exposed gill filaments. Thirty minutes of moderate (7 kPa pO2) and severe hypoxia (1 kPa pO2) caused 1.6- and 2.4-fold increase, respectively, of NO accumulation in the endothelial muscle cells of the hemolymphatic vessels of the gill filaments. This led to a dilatation of blood vessel diameter by 43% (7 kPa) and 56% (1 kPa), which facilitates blood flow. Experiments in which we applied the chemical NO-donor Spermine NONOate (concentrations ranging from 1 to 6 mM) under normoxic conditions corroborate the dilatational effect of NO on the blood vessel. The formation of within the filament epithelial cells increased 1.5 (7 kPa) and 2-fold (1 kPa) upon treatment. Biochemical analysis of mitochondrial electron transport complexes in hypoxia-exposed gill tissue indicates decreased activity of complexes I and III in both hypoxic conditions; whereas complex IV (cytochrome-c oxidase) activity increased at 7 kPa and decreased at 1 kPa compared to normoxic exposure conditions. This corresponds to the pattern of pO2-dependent gill respiration rates recorded in ex-vivo experiments. Severe hypoxia (1 kPa) appears to have a stabilizing effect on NO accumulation in gill cells, since less O2 is available for NO oxidation to nitrite/nitrate. Hypoxia thus supports the NO dependent inhibition of complex IV activity, a mechanism that could fine tune mitochondrial respiration to the local O2 availability in a tissue. Our study highlights a basal function of NO in improving perfusion of hypoxic invertebrate tissues, which could be a key mechanism of tolerance toward environmental O2 variations.

A new species of Simulium (Gomphostilbia) (Diptera: Simuliidae)from South India.

Simulium (Gomphostilbia) kumbakkaraiense sp. n. is described based on adults, pupae and mature larvae from Kumbakkarai stream, in the Palani Hills of Western Ghats, South India. This new species is placed in the Simulium batoense species-group of the subgenus Gomphostilbia Enderlein. This new species is characterized by a scutum with three brownish-black longitudinal vittae and hind basitarsus in the female 5.3 times as long as wide, and in male the large facets of the upper eye in 13 vertical columns and 14 horizontal rows, the respiratory gill with short common basal in the pupa and postgenal cleft arrow-head-shaped in the larva. Taxonomic notes are provided to distinguish this new species from related species. [Zoobank register: http://zoobank.org/urn:lsid:zoobank.org:act:C575FB25-B6B2-414B-AE11-0468A1871DFA].