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Aaskov ML, Jensen RJ, Skov PV, Wood CM, Wang T, Malte H, Bayley M. Arapaima gigas maintains gas exchange separation in severe aquatic hypoxia but does not suffer branchial oxygen loss. J Exp Biol 2022; 225:274291. [PMID: 35132994 DOI: 10.1242/jeb.243672] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/19/2021] [Accepted: 02/02/2022] [Indexed: 11/20/2022]
Abstract
One of the most air-reliant obligate air-breathing fish is the South American Arapaima gigas, with substantially reduced gills impeding gas diffusion, thought to be a result of recurring aquatic hypoxia in its habitat. In normoxic water, A. gigas is reported to satisfy 70-80% of its O2 requirement from the air while excreting 60-90% of its CO2 to the water. If this pattern of gas exchange were to continue in severely hypoxic water, O2 loss at the gills would be expected. We hypothesized therefore that partitioning of CO2 would shift to the air phase in severe aquatic hypoxia eliminating the risk of branchial O2 loss. By adapting a respirometer designed to measure aquatic MO2/MCO2 we were able to run intermittent closed respirometry on both water and air phase for both of these gasses as well as sample water for N-waste measurements (ammonia-N, urea-N) so as to calculate metabolic fuel utilization. In contrast to our prediction, we found that partitioning of CO2 excretion changed little between normoxia and severe hypoxia (83% vs 77% aquatic excretion respectively) and at the same time there was no evidence of branchial O2 loss in hypoxia. This indicates that A. gigas can utilize distinct transfer pathways for O2 and CO2. Routine and standard MO2, N-waste excretion, and metabolic fuel utilization did not change with water oxygenation. Metabolism was fueled mostly by protein oxidation (53%) while carbohydrates and lipids accounted for 27% and 20% respectively.
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Affiliation(s)
- Magnus L Aaskov
- Zoophysiology, Department of Biology, Aarhus University, Aarhus, Denmark
| | - Rasmus J Jensen
- Zoophysiology, Department of Biology, Aarhus University, Aarhus, Denmark
| | - Peter Vilhelm Skov
- Technical University of Denmark, DTU Aqua, Section for Aquaculture, Hirtshals, Denmark
| | - Chris M Wood
- Department of Zoology, University of British Columbia, Vancouver, BC V6T 1Z4, Canada
| | - Tobias Wang
- Zoophysiology, Department of Biology, Aarhus University, Aarhus, Denmark
| | - Hans Malte
- Zoophysiology, Department of Biology, Aarhus University, Aarhus, Denmark
| | - Mark Bayley
- Zoophysiology, Department of Biology, Aarhus University, Aarhus, Denmark
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2
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Frommel AY, Kwan GT, Prime KJ, Tresguerres M, Lauridsen H, Val AL, Gonçalves LU, Brauner CJ. Changes in gill and air-breathing organ characteristics during the transition from water- to air-breathing in juvenile Arapaima gigas. JOURNAL OF EXPERIMENTAL ZOOLOGY PART 2021; 335:801-813. [PMID: 33819380 DOI: 10.1002/jez.2456] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/29/2020] [Revised: 02/10/2021] [Accepted: 02/25/2021] [Indexed: 01/01/2023]
Abstract
The obligate air-breathing Amazonian fish, Arapaima gigas, hatch as water-breathing larvae but with development, they modify their swim bladder to an air-breathing organ (ABO) while reducing their gill filaments to avoid oxygen loss. Here, we show that significant changes already take place between 4 weeks (1.6 g) and 11 weeks (5 g) post hatch, with a reduction in gill lamellar surface area, increase in gill diffusion distance, and proliferation of the parenchyma in the ABO. By using a variety of methods, we quantified the surface area and diffusion distances of the gills and skin, and the swim bladder volume and anatomical complexity from hatch to 11-week-old juveniles. In addition, we identified the presence of two ionocyte types in the gills and show how these change with development. Until 1.6 g, A. gigas possess only the H+ -excreting/Na+ -absorbing type, while 5-g fish and adults have an additional ionocyte which likely absorbs H+ and Cl- and excretes HCO3 - . The ionocyte density on the gill filaments increased with age and is likely a compensatory mechanism for maintaining ion transport while reducing gill surface area. In the transition from water- to air-breathing, A. gigas likely employs a trimodal respiration utilizing gills, skin, and ABO and thus avoid a respiratory-ion regulatory compromise at the gills.
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Affiliation(s)
- Andrea Y Frommel
- Department of Zoology, University of British Columbia, Vancouver, British Columbia, Canada.,Institute of Oceans and Fisheries, University of British Columbia, Vancouver, British Columbia, Canada
| | - Garfield T Kwan
- Marine Biology Research Division, Scripps Institution of Oceanography, University of California San Diego, La Jolla, California, USA
| | - Kaelan J Prime
- Marine Biology Research Division, Scripps Institution of Oceanography, University of California San Diego, La Jolla, California, USA
| | - Martin Tresguerres
- Marine Biology Research Division, Scripps Institution of Oceanography, University of California San Diego, La Jolla, California, USA
| | - Henrik Lauridsen
- Department of Clinical Medicine (Comparative Medicine Lab), Aarhus University, Aarhus, Denmark
| | - Adalberto L Val
- Brazilian National Institute for Research of the Amazon, Manaus, Amazonas, Brazil
| | - Ligia U Gonçalves
- Brazilian National Institute for Research of the Amazon, Manaus, Amazonas, Brazil
| | - Colin J Brauner
- Department of Zoology, University of British Columbia, Vancouver, British Columbia, Canada
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3
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Ma X, Shang M, Su B, Wiley A, Bangs M, Alston V, Simora RM, Nguyen MT, Backenstose NJC, Moss AG, Duong TY, Wang X, Dunham RA. Comparative Transcriptome Analysis During the Seven Developmental Stages of Channel Catfish ( Ictalurus punctatus) and Tra Catfish ( Pangasianodon hypophthalmus) Provides Novel Insights for Terrestrial Adaptation. Front Genet 2021; 11:608325. [PMID: 33552125 PMCID: PMC7859520 DOI: 10.3389/fgene.2020.608325] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/20/2020] [Accepted: 12/17/2020] [Indexed: 11/25/2022] Open
Abstract
Tra catfish (Pangasianodon hypophthalmus), also known as striped catfish, is a facultative air-breather that uses its swim bladder as an air-breathing organ (ABO). A related species in the same order (Siluriformes), channel catfish (Ictalurus punctatus), does not possess an ABO and thus cannot breathe in the air. Tra and channel catfish serve as great comparative models for investigating possible genetic underpinnings of aquatic to land transitions, as well as for understanding genes that are crucial for the development of the swim bladder and the function of air-breathing in tra catfish. In this study, hypoxia challenge and microtomy experiments collectively revealed critical time points for the development of the air-breathing function and swim bladder in tra catfish. Seven developmental stages in tra catfish were selected for RNA-seq analysis based on their transition to a stage that could live at 0 ppm oxygen. More than 587 million sequencing clean reads were generated, and a total of 21,448 unique genes were detected. A comparative genomic analysis between channel catfish and tra catfish revealed 76 genes that were present in tra catfish, but absent from channel catfish. In order to further narrow down the list of these candidate genes, gene expression analysis was performed for these tra catfish-specific genes. Fourteen genes were inferred to be important for air-breathing. Of these, HRG, GRP, and CX3CL1 were identified to be the most likely genes related to air-breathing ability in tra catfish. This study provides a foundational data resource for functional genomic studies in air-breathing function in tra catfish and sheds light on the adaptation of aquatic organisms to the terrestrial environment.
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Affiliation(s)
- Xiaoli Ma
- School of Fisheries, Aquaculture and Aquatic Sciences, Auburn University, Auburn, AL, United States.,Alabama Agricultural Experiment Station, Auburn, AL, United States
| | - Mei Shang
- School of Fisheries, Aquaculture and Aquatic Sciences, Auburn University, Auburn, AL, United States.,Alabama Agricultural Experiment Station, Auburn, AL, United States
| | - Baofeng Su
- School of Fisheries, Aquaculture and Aquatic Sciences, Auburn University, Auburn, AL, United States.,Alabama Agricultural Experiment Station, Auburn, AL, United States
| | - Anne Wiley
- Department of Anatomy, Physiology and Pharmacology, Auburn University, Auburn, AL, United States
| | - Max Bangs
- School of Fisheries, Aquaculture and Aquatic Sciences, Auburn University, Auburn, AL, United States.,Alabama Agricultural Experiment Station, Auburn, AL, United States.,Department of Biological Science, Florida State University, Tallahassee, FL, United States
| | - Veronica Alston
- School of Fisheries, Aquaculture and Aquatic Sciences, Auburn University, Auburn, AL, United States.,Alabama Agricultural Experiment Station, Auburn, AL, United States
| | - Rhoda Mae Simora
- School of Fisheries, Aquaculture and Aquatic Sciences, Auburn University, Auburn, AL, United States.,Alabama Agricultural Experiment Station, Auburn, AL, United States.,College of Fisheries and Ocean Sciences, University of the Philippines Visayas, Miagao, Philippines
| | - Mai Thi Nguyen
- College of Aquaculture and Fisheries, Can Tho University, Can Tho, Vietnam
| | - Nathan J C Backenstose
- School of Fisheries, Aquaculture and Aquatic Sciences, Auburn University, Auburn, AL, United States.,Alabama Agricultural Experiment Station, Auburn, AL, United States.,Department of Biological Sciences, University at Buffalo, Buffalo, NY, United States
| | - Anthony G Moss
- Alabama Agricultural Experiment Station, Auburn, AL, United States.,Department of Biological Sciences, Auburn University, Auburn, AL, United States
| | - Thuy-Yen Duong
- College of Aquaculture and Fisheries, Can Tho University, Can Tho, Vietnam
| | - Xu Wang
- Alabama Agricultural Experiment Station, Auburn, AL, United States.,Department of Pathobiology, Auburn University, Auburn, AL, United States.,HudsonAlpha Institute for Biotechnology, Huntsville, AL, United States
| | - Rex A Dunham
- School of Fisheries, Aquaculture and Aquatic Sciences, Auburn University, Auburn, AL, United States.,Alabama Agricultural Experiment Station, Auburn, AL, United States
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4
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Fiedler S, Wünnemann H, Hofmann I, Theobalt N, Feuchtinger A, Walch A, Schwaiger J, Wanke R, Blutke A. A practical guide to unbiased quantitative morphological analyses of the gills of rainbow trout (Oncorhynchus mykiss) in ecotoxicological studies. PLoS One 2020; 15:e0243462. [PMID: 33296424 PMCID: PMC7725368 DOI: 10.1371/journal.pone.0243462] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2020] [Accepted: 11/21/2020] [Indexed: 12/28/2022] Open
Abstract
Rainbow trout (Oncorhynchus mykiss) are frequently used as experimental animals in ecotoxicological studies, in which they are experimentally exposed to defined concentrations of test substances, such as heavy metals, pesticides, or pharmaceuticals. Following exposure to a broad variety of aquatic pollutants, early morphologically detectable toxic effects often manifest in alterations of the gills. Suitable methods for an accurate and unbiased quantitative characterization of the type and the extent of morphological gill alterations are therefore essential prerequisites for recognition, objective evaluation and comparison of the severity of gill lesions. The aim of the present guidelines is to provide practicable, standardized and detailed protocols for the application of unbiased quantitative stereological analyses of relevant morphological parameters of the gills of rainbow trout. These gill parameters inter alia include the total volume of the primary and secondary gill lamellae, the surface area of the secondary gill lamellae epithelium (i.e., the respiratory surface) and the thickness of the diffusion barrier. The featured protocols are adapted to fish of frequently used body size classes (300-2000 g). They include well-established, conventional sampling methods, probes and test systems for unbiased quantitative stereological analyses of light- and electron microscopic 2-D gill sections, as well as the application of modern 3-D light sheet fluorescence microscopy (LSFM) of optically cleared gill samples as an innovative, fast and efficient quantitative morphological analysis approach. The methods shown here provide a basis for standardized and representative state-of-the-art quantitative morphological analyses of trout gills, ensuring the unbiasedness and reproducibility, as well as the intra- and inter-study comparability of analyses results. Their broad implementation will therefore significantly contribute to the reliable identification of no observed effect concentration (NOEC) limits in ecotoxicological studies and, moreover, to limit the number of experimental animals by reduction of unnecessary repetition of experiments.
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Affiliation(s)
- Sonja Fiedler
- Institute of Veterinary Pathology at the Center for Clinical Veterinary Medicine, Ludwig-Maximilians-Universität München, Munich, Germany
| | - Hannah Wünnemann
- Unit 73 Aquatic Ecotoxicology, Microbial Ecology, Bavarian Environment Agency, Wielenbach, Germany
| | - Isabel Hofmann
- Institute of Veterinary Pathology at the Center for Clinical Veterinary Medicine, Ludwig-Maximilians-Universität München, Munich, Germany
| | - Natalie Theobalt
- Institute of Veterinary Pathology at the Center for Clinical Veterinary Medicine, Ludwig-Maximilians-Universität München, Munich, Germany
| | - Annette Feuchtinger
- Research Unit Analytical Pathology, Helmholtz Zentrum München, Neuherberg, Germany
| | - Axel Walch
- Research Unit Analytical Pathology, Helmholtz Zentrum München, Neuherberg, Germany
| | - Julia Schwaiger
- Unit 73 Aquatic Ecotoxicology, Microbial Ecology, Bavarian Environment Agency, Wielenbach, Germany
| | - Rüdiger Wanke
- Institute of Veterinary Pathology at the Center for Clinical Veterinary Medicine, Ludwig-Maximilians-Universität München, Munich, Germany
| | - Andreas Blutke
- Research Unit Analytical Pathology, Helmholtz Zentrum München, Neuherberg, Germany
- * E-mail:
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Gam LTH, Thanh Huong DT, Tuong DD, Phuong NT, Jensen FB, Wang T, Bayley M. Effects of temperature on acid-base regulation, gill ventilation and air breathing in the clown knifefish, Chitala ornata. J Exp Biol 2020; 223:jeb216481. [PMID: 32001546 DOI: 10.1242/jeb.216481] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/11/2019] [Accepted: 01/23/2020] [Indexed: 11/20/2022]
Abstract
Chitala ornata is a facultative air-breathing fish, which at low temperatures shows an arterial PCO2 (PaCO2 ) level only slightly elevated above that of water breathers. By holding fish with in-dwelling catheters at temperatures from 25 to 36°C and measuring blood gasses, we show that this animal follows the ubiquitous poikilotherm pattern of reducing arterial pH with increasing temperature. Surprisingly, the temperature increase caused an elevation of PaCO2 from 5 to 12 mmHg while the plasma bicarbonate concentration remained constant at around 8 mmol l-1 The temperature increase also gave rise to a larger fractional increase in air breathing than in gill ventilation frequency. These findings suggest that air breathing, and hence the partitioning of gas exchange, is to some extent regulated by acid-base status in air-breathing fish and that these bimodal breathers will be increasingly likely to adopt respiratory pH control as temperature rises, providing an interesting avenue for future research.
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Affiliation(s)
- Le Thi Hong Gam
- College of Aquaculture and Fisheries, Can Tho University, Can Tho City, Vietnam
| | - Do Thi Thanh Huong
- College of Aquaculture and Fisheries, Can Tho University, Can Tho City, Vietnam
| | - Dang Diem Tuong
- College of Aquaculture and Fisheries, Can Tho University, Can Tho City, Vietnam
| | - Nguyen Thanh Phuong
- College of Aquaculture and Fisheries, Can Tho University, Can Tho City, Vietnam
| | - Frank Bo Jensen
- Department of Biology, University of Southern Denmark, 5230 Odense, Denmark
| | - Tobias Wang
- Zoophysiology, Department of Bioscience, Aarhus University, 8000 Aarhus, Denmark
- Aarhus Institute of Advanced Studies, 8000 Aarhus C, Denmark
| | - Mark Bayley
- Zoophysiology, Department of Bioscience, Aarhus University, 8000 Aarhus, Denmark
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6
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Turko AJ, Maini P, Wright PA, Standen EM. Gill remodelling during terrestrial acclimation in the amphibious fish Polypterus senegalus. J Morphol 2019; 280:329-338. [PMID: 30707482 DOI: 10.1002/jmor.20946] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/22/2018] [Revised: 12/12/2018] [Accepted: 12/19/2018] [Indexed: 12/19/2022]
Abstract
Fishes are effectively weightless in water due to the buoyant support of the environment, but amphibious fishes must cope with increased effective weight when on land. Delicate structures such as gills are especially vulnerable to collapse and loss of surface area out of water. We tested the 'structural support' hypothesis that amphibious Polypterus senegalus solve this problem using phenotypically plastic changes that provide mechanical support and increase stiffness at the level of the gill lamellae, the filaments, and the whole arches. After 7 d in terrestrial conditions, enlargement of an inter-lamellar cell mass filled the water channels between gill lamellae, possibly to provide structural support and/or reduce evaporative water loss. Similar gill remodelling has been described in several other actinopterygian fishes, suggesting this may be an ancestral trait. There was no change in the mechanical properties or collagen composition of filaments or arches after 7 days out of water, but 8 months of terrestrial acclimation caused a reduction in gill arch length and mineralized bone volume. Thus, rather than increasing the size and stiffness of the gill skeleton, P. senegalus may instead reduce investment in supportive gill tissue while on land. These results are strikingly similar to the evolutionary trend of gill loss that occurred during the tetrapod invasion of land, raising the possibility that genetic assimilation of gill plasticity was an underlying mechanism.
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Affiliation(s)
- Andy J Turko
- Department of Integrative Biology, University of Guelph, Guelph, Ontario, Canada
| | - Priyam Maini
- Department of Biology, University of Ottawa, Ottawa, Ontario, Canada
| | - Patricia A Wright
- Department of Integrative Biology, University of Guelph, Guelph, Ontario, Canada
| | - Emily M Standen
- Department of Biology, University of Ottawa, Ottawa, Ontario, Canada
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7
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Bayley M, Damsgaard C, Thomsen M, Malte H, Wang T. Learning to Air-Breathe: The First Steps. Physiology (Bethesda) 2019; 34:14-29. [DOI: 10.1152/physiol.00028.2018] [Citation(s) in RCA: 33] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023] Open
Abstract
Air-breathing in vertebrates has evolved many times among the bony fish while in water. Its appearance has had a fundamental impact on the regulation of ventilation and acid-base status. We review the physico-chemical constraints imposed by water and air, place the extant air-breathing fish into this framework, and show how that the advantages of combining control of ventilation and acid-base status are only available to the most obligate of air-breathing fish, thus highlighting promising avenues for research.
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Affiliation(s)
- Mark Bayley
- Section for Zoophysiology, Department of Bioscience, Aarhus University, Aarhus, Denmark
| | - Christian Damsgaard
- Department of Zoology, University of British Columbia, Vancouver, British Columbia, Canada
| | - Mikkel Thomsen
- Section for Zoophysiology, Department of Bioscience, Aarhus University, Aarhus, Denmark
| | - Hans Malte
- Section for Zoophysiology, Department of Bioscience, Aarhus University, Aarhus, Denmark
| | - Tobias Wang
- Section for Zoophysiology, Department of Bioscience, Aarhus University, Aarhus, Denmark
- Aarhus Institute of Advanced Sciences, Aarhus University, Aarhus, Denmark
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8
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Mbanga B, van Dyk C, Maina JN. Morphometric and morphological study of the respiratory organs of the bimodally-breathing African sharptooth catfish (Clarias gariepinus): Burchell (1822). ZOOLOGY 2018; 130:6-18. [PMID: 30502840 DOI: 10.1016/j.zool.2018.07.005] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/07/2018] [Revised: 07/17/2018] [Accepted: 07/19/2018] [Indexed: 12/01/2022]
Abstract
The respiratory organs of the African sharptooth catfish, Clarias gariepinus, were studied to broaden existing understanding of the adaptive stratagems that have evolved for air-breathing in fish. The gills were well-developed and the air-breathing organs (ABOs) comprised labyrinthine organs (LOs), suprabranchial chamber membranes (SBCMs) and gill fans (GFns). Respectively, the gills and the LOs had the highest mass-specific respiratory surface areas of 133.7 and 141.9 mm2 per gram and among the ABOs, with a harmonic mean thickness of the blood-barrier (BGB) of 0.39 μm, the LOs had the thinnest BGB followed by the GFns (0.48 μm) and the SBCMs (0.49 μm): the water-blood barrier of the gills was relatively much thicker (7.93 μm). Vindicating why C. gariepinus is an obligate air-breather, the total mass-specific morphometric (anatomical) diffusing capacity of the ABOs for O2 per unit body weight (W) (Dto2/W) comprised 90.5% of the mean total value for all the respiratory organs. Compared with the East African catfish, Clarias mossambicus, the Dto2/W of the ABOs of C. gariepinus was 5.7 times greater. The difference between the two species of fish may be explained by the physicochemical differences of the aquatic habitats they occupy: the former occupies a seasonal river which dries up during the summer months leaving shallow pools of water in which the O2 concentrations are very low and CO2 very high while the later populates a highly eutrophic dam where the O2 levels greatly fluctuate seasonally.
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Affiliation(s)
- Blandine Mbanga
- Department of Zoology, University of Johannesburg, Auckland Park Campus 2006, Kingsway, Johannesburg, South Africa
| | - Cobus van Dyk
- Department of Zoology, University of Johannesburg, Auckland Park Campus 2006, Kingsway, Johannesburg, South Africa
| | - John N Maina
- Department of Zoology, University of Johannesburg, Auckland Park Campus 2006, Kingsway, Johannesburg, South Africa.
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Gam LTH, Jensen FB, Huong DTT, Phuong NT, Bayley M. The effects of elevated environmental CO 2 on nitrite uptake in the air-breathing clown knifefish, Chitala ornata. AQUATIC TOXICOLOGY (AMSTERDAM, NETHERLANDS) 2018; 196:124-131. [PMID: 29367072 DOI: 10.1016/j.aquatox.2018.01.011] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/30/2017] [Revised: 01/09/2018] [Accepted: 01/13/2018] [Indexed: 06/07/2023]
Abstract
Nitrite and carbon dioxide are common environmental contaminants in the intensive aquaculture ponds used to farm clown knifefish (Chitala ornata) in the Mekong delta, Vietnam. Here we tested the hypothesis that hypercapnia reduces nitrite uptake across the gills, because pH regulation will reduce chloride uptake and hence nitrite uptake as the two ions compete for the same transport route via the branchial HCO3-/Cl- exchanger. Fish fitted with arterial catheters were exposed to normocapnic/normoxic water (control), nitrite (1 mM), hypercapnia (21 mmHg CO2), or combined hypercapnia (acclimated hypercapnia) and nitrite for 96 h. Blood was sampled to measure acid-base status, haemoglobin derivatives and plasma ions. Plasma nitrite increased for 48 h, but levels stayed below the exposure concentration, and subsequently decreased as a result of nitrite detoxification to nitrate. The total uptake of nitrite (evaluated as [NO2-] + [NO3-]) was significantly decreased in hypercapnia, in accordance with the hypothesis. Methemoglobin and nitrosylhemoglobin levels were similarly lower during hypercapnic compared to normocapnic nitrite exposure. The respiratory acidosis induced by hypercapnia was half-compensated by bicarbonate accumulation in 96 h, which was mainly chloride-mediated (i.e. reduced Cl- influx via the branchial HCO3-/Cl- exchanger). Plasma osmolality and main ions (Na+, Cl-) were significantly decreased by hypercapnia and by nitrite exposure, consistent with inhibition of active transport. We conclude that hypercapnia induces a long-lasting, and mainly chloride-mediated acid-base regulation that reduces the uptake of nitrite across the gills.
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Affiliation(s)
- Le Thi Hong Gam
- College of Aquaculture and Fisheries, Can Tho University, Can Tho City, Viet Nam
| | - Frank Bo Jensen
- Department of Biology, University of Southern Denmark, Odense, Denmark
| | - Do Thi Thanh Huong
- College of Aquaculture and Fisheries, Can Tho University, Can Tho City, Viet Nam
| | - Nguyen Thanh Phuong
- College of Aquaculture and Fisheries, Can Tho University, Can Tho City, Viet Nam
| | - Mark Bayley
- Zoophysiology, Department of Bioscience, Aarhus University, Building 1131 C.F. Møllers Allé 3, DK-8000 Aarhus C., Denmark.
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