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In hypoxia, air-breathing fish obtain O2from the air but continue to excrete CO2into the water. Consequently, it is believed that some O2obtained by air-breathing is lost at the gills in hypoxic water.Pangasionodon hypophthalmusis an air-breathing catfish with very large gills from the Mekong River basin where it is cultured in hypoxic ponds. To understand howP. hypophthalmuscan maintain high growth in hypoxia with the presumed O2loss, 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 O2uptake, while maintaining aquatic CO2excretion at 91% of the total. Further, even small elevations in water PO2rapidly 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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Functional Morphology of the Urohyal Shunt for Symmetrical and Asymmetrical Ventilation in the Flatfish, Isopsetta isolepis
Abstract Flatfishes are benthic fishes that are well known for their ability to bury in the sediment, making the transition from above to below the sediment in a matter of seconds. Laterally flattened bodies allow flatfishes to lay flush against the substrate, a behavior facilitated by having an asymmetrical neurocranium with two eyes on one side of the head. Despite neurocranial asymmetry, their gill chambers are highly symmetrical. Additionally, most flatfishes have a uniquely shaped urohyal bone that forms passageway for water to travel ventrally between the “eyed-side” and “blind-side” gill chambers. Our study examines whether the kinematics and pressures generated by the gill chambers are also symmetrical during breathing above and below the sediment and during rapid burial in sediment. We studied Isopsetta isolepis individuals using sonomicrometry crystals to measure the changes in positions of the opercle bones relative to the urohyal and pressure transducers to record gill chamber pressures during burial. We conclude I. isolepis exhibit both symmetrical and asymmetrical breathing above and below the sediment. Pressures and movements were highly asymmetrical during burial jetting. We observed motions that indicate that the urohyal is an active shunt to allow passage of water between the eyed to the blind-side gill chambers.
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- PAR ID:
- 10410274
- Date Published:
- Journal Name:
- Integrative and Comparative Biology
- Volume:
- 62
- Issue:
- 4
- ISSN:
- 1540-7063
- Page Range / eLocation ID:
- 897 to 907
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
-
Accepted Manuscript
- Journal Article:
- https://doi.org/10.1093/icb/icac126
