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Aaskov ML, Nelson D, Lauridsen H, Huong DTT, Ishimatsu A, Crossley DA, Malte H, Bayley M. Do air-breathing fish suffer branchial oxygen loss in hypoxic water? Proc Biol Sci 2023; 290:20231353. [PMID: 37700647 PMCID: PMC10498054 DOI: 10.1098/rspb.2023.1353] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/16/2023] [Accepted: 08/18/2023] [Indexed: 09/14/2023] Open
Abstract
In hypoxia, air-breathing fish obtain O2 from the air but continue to excrete CO2 into the water. Consequently, it is believed that some O2 obtained by air-breathing is lost at the gills in hypoxic water. Pangasionodon hypophthalmus is an air-breathing catfish with very large gills from the Mekong River basin where it is cultured in hypoxic ponds. To understand how P. hypophthalmus can maintain high growth in hypoxia with the presumed O2 loss, we quantified respiratory gas exchange in air and water. In severe hypoxia (PO2: ≈ 1.5 mmHg), it lost a mere 4.9% of its aerial O2 uptake, while maintaining aquatic CO2 excretion at 91% of the total. Further, even small elevations in water PO2 rapidly reduced this minor loss. Charting the cardiovascular bauplan across the branchial basket showed four ventral aortas leaving the bulbus arteriosus, with the first and second gill arches draining into the dorsal aorta while the third and fourth gill arches drain into the coeliacomesenteric artery supplying the gut and the highly trabeculated respiratory swim-bladder. Substantial flow changes across these two arterial systems from normoxic to hypoxic water were not found. We conclude that the proposed branchial oxygen loss in air-breathing fish is likely only a minor inefficiency.
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Affiliation(s)
- Magnus L. Aaskov
- Division of Zoophysiology, Department of Biology, Aarhus University, 8000C Aarhus, Denmark
| | - Derek Nelson
- Department of Biological Sciences, University of North Texas, 1155 Union Circle, Denton, TX 76203, USA
| | - Henrik Lauridsen
- Comparative Medicine Lab, Department of Clinical Medicine, Aarhus, Denmark
| | - Do Thi Thanh Huong
- College of Aquaculture and Fisheries, Can Tho University, Can Tho, Vietnam
| | - Atsushi Ishimatsu
- Institute for East China Sea Research, Nagasaki University, Nagasaki, Japan
| | - Dane A. Crossley
- Department of Biological Sciences, University of North Texas, 1155 Union Circle, Denton, TX 76203, USA
| | - Hans Malte
- Division of Zoophysiology, Department of Biology, Aarhus University, 8000C Aarhus, Denmark
| | - Mark Bayley
- Division of Zoophysiology, Department of Biology, Aarhus University, 8000C Aarhus, Denmark
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Vieira LS, Vaz DFB, Netto-Ferreira AL. Ontogeny of the swim bladder of the Plainfin Midshipman, Porichthys notatus (Percomorphacea: Batrachoidiformes). ZOOLOGY 2023; 159:126102. [PMID: 37364349 DOI: 10.1016/j.zool.2023.126102] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2022] [Revised: 06/09/2023] [Accepted: 06/14/2023] [Indexed: 06/28/2023]
Abstract
The batracoidid Plainfin Midshipmen Porichthys notatus Girard has been extensively studied due to the sound production abilities and specializations of its swim bladder. The present study describes three-dimensional variations of the morphology of the swim bladder and sonic muscles of P. notatus during its post-hatch larval development, with the use of three-dimensional computed tomography. This study also includes descriptions of the relative position of the swim bladder to other visceral organs. The swim bladder, digestive tract, and liver were already present in the smallest examined specimens (5.9 mm; newly hatched larvae) along with the yolk sac. In the smallest specimens, the digestive tract is straight, but from 7.1 mm TL, the digestive tract forms the first intestinal loops, and at 25.5 mm TL, a second intestinal loop. In smallest specimens, the swim bladder is oval, but at 7.1 mm TL, the anterior margin starts invaginating, forming a pair of anterior lobes. The first appearance of the intrinsic sonic muscles in swim bladder occurs at 13.1 mm TL. Additionally, we provide comparisons between the shape of the swim bladder of P. notatus and other species. The shape of the swim bladder of P. notatus and other members of Porichthyinae have an ovoid posterior region with two anterior lobes and differs from the cordiform or semiconected/bilobed the swim bladders observed in the other Batrachoididae.
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Affiliation(s)
- Lorena S Vieira
- Laboratório de Ictiologia, Departamento de Zoologia, Universidade Federal do Rio Grande do Sul., Av. Bento Gonçalves 9500, Porto Alegre, RS, Brazil.
| | - Diego F B Vaz
- Museum of Comparative Zoology, Harvard University, 26 Oxford Street, Cambridge, MA 02138, United States; Guam Ecosystems Collaboratorium Biorepository, Guam EPSCoR, University of Guam. 303 University Drive, UOG Station, Mangilao, Guam 96923, United States
| | - Andre L Netto-Ferreira
- Laboratório de Ictiologia, Departamento de Zoologia, Universidade Federal do Rio Grande do Sul., Av. Bento Gonçalves 9500, Porto Alegre, RS, Brazil
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The Alimentary Tract of African Bony-Tongue, Heterotis niloticus (Cuvier, 1829): Morphology Study. Animals (Basel) 2022; 12:ani12121565. [PMID: 35739901 PMCID: PMC9219464 DOI: 10.3390/ani12121565] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/2022] [Revised: 06/06/2022] [Accepted: 06/15/2022] [Indexed: 11/21/2022] Open
Abstract
Simple Summary Heterotis niloticus is a primitive freshwater teleost. It is a candidate for aquaculture in Africa with a good conversion rate and is used for evolutionary studies for its anatomical similarities with reptiles and birds. H. niloticus is also an endangered species for several reasons, including overexploitation. The purpose of the present study was to investigate, by gross anatomy and light microscope analysis, the morphological structure of the digestive system of the African bony-tongue, from the oropharyngeal cavity to the rectum, including its associated glands. A peculiar feature of this species is the presence of both bone trabeculae and well-defined cartilaginous areas in the process of ossification, in the deeper layers of the tongue. The so-called “African bony- tongue” is due to these characteristics. On both sides of the tongue, two tubular structures covered by numerous taste buds, as well as mucous cells, were found. The presence of well-defined lymphoid tissue in both pyloric ceca and rectum is described for the first time. Further investigations could aim to optimize husbandry and feeding protocols permitting, also, to understand the evolutionary process. Abstract A morphological study of the alimentary tract, from the oropharyngeal cavity to the rectum, including the attached glands, of African bony-tongue, Heterotis niloticus (Cuvier, 1829) was carried out by gross anatomy, and light microscope analysis. This study aimed to give a deeper knowledge of the alimentary tract morphological features of this species of commercial interest. H. niloticus is distinguished by individual morphological characteristics showing a digestive tract similar to that of reptiles and birds. Within the oropharyngeal cavity, two tubular structures with digitiform ends are arranged on both lateral sides of the triangular tongue. The oropharyngeal cavity connects the stomach by a short esophagus. This latter is adapted to mechanical trituration, and it is divided into a pars glandularis and a thick-walled pars muscularis. The gizzard flows into the anterior intestine and two blind pyloric appendages, which exhibit specific functions, including immune defense for the presence of secondary lymphoid organs. The anterior intestine continues with the middle and posterior tracts up into the rectum. According to the histological observations, all regions of the alimentary tract have common structural features, typical of hollow organs, with differences in the mucosa structure that reflects the different functions of the apparatus, from mouth to anus. Within this study, we provided the first basis for future studies on optimizing rearing conditions, feed conversion ratio, and the digestive capacity, improving the growth performance of this species, and ensuring its conservation.
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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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Wood CM, Pelster B, Braz-Mota S, Val AL. Gills versus kidney for ionoregulation in the obligate air-breathing Arapaima gigas, a fish with a kidney in its air-breathing organ. J Exp Biol 2020; 223:jeb232694. [PMID: 32895323 DOI: 10.1242/jeb.232694] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/04/2020] [Accepted: 08/19/2020] [Indexed: 12/19/2022]
Abstract
In Arapaima gigas, an obligate air-breather endemic to ion-poor Amazonian waters, a large complex kidney runs through the air-breathing organ (ABO). Previous indirect evidence suggested that the kidney, relative to the small gills, may be exceptionally important in ionoregulation and nitrogen (N) waste excretion, with support of kidney function by direct O2 supply from the airspace. We tested these ideas by continuous urine collection and gill flux measurements in ∼700 g fish. ATPase activities were many-fold greater in kidney than gills. In normoxia, gill Na+ influx and efflux were in balance, with net losses of Cl- and K+ Urine flow rate (UFR, ∼11 ml kg-1 h-1) and urinary ions (< 0.2 mmol l-1) were exceptional, with [urine]:[plasma] ratios of 0.02-0.002 for K+, Na+, and Cl-, indicating strong reabsorption with negligible urinary ion losses. Urinary [ammonia] was very high (10 mmol l-1, [urine]:[plasma] ∼17) indicating strong secretion. The kidney accounted for 21-24% of N excretion, with ammonia dominating (95%) over urea-N through both routes. High urinary [ammonia] was coupled to high urinary [HCO3-]. Aerial hypoxia (15.3 kPa) and aerial hyperoxia (>40.9 kPa) had no effects on UFR, but both inhibited branchial Na+ influx, revealing novel aspects of the osmorespiratory compromise. Aquatic hypoxia (4.1 kPa), but not aquatic hyperoxia (>40.9 kPa), inhibited gill Na+ influx, UFR and branchial and urinary ammonia excretion. We conclude that the kidney is more important than gills in ionoregulation, and is significant in N excretion. Although not definitive, our results do not indicate direct O2 supply from the ABO for kidney function.
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Affiliation(s)
- Chris M Wood
- Department of Zoology, University of British Columbia, Vancouver, BC, Canada V6T 1Z4
- Department of Biology, McMaster University, Hamilton, ON, Canada L8S 4K1
| | - Bernd Pelster
- Institute of Zoology, University of Innsbruck, Innsbruck A-6020, Austria
- Center for Molecular Biosciences, University Innsbruck, Innsbruck A-6020, Austria
| | - Susana Braz-Mota
- Laboratory of Ecophysiology and Molecular Evolution, Brazilian National Institute for Research of the Amazon, Manaus 69080-971, Brazil
| | - Adalberto L Val
- Laboratory of Ecophysiology and Molecular Evolution, Brazilian National Institute for Research of the Amazon, Manaus 69080-971, Brazil
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