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Published on: August 16, 2018
Evolutionary aspects of intestinal bicarbonate secretion in fish
Josi R Taylor1, Martin Grosell
1RSMAS, University of Miami, Miami, FL 33149, USA. jtaylor@rsmas.miami.edu
Summary
Marine fish, including sharks and sturgeon, use intestinal bicarbonate secretion to manage salt balance and osmoregulation when drinking seawater. This vital process helps maintain hydromineral homeostasis across diverse fish species.
Area of Science:
- Comparative physiology
- Fish osmoregulation
- Marine biology
Background:
- Marine fish drink seawater to meet hydration needs.
- Intestinal ion and water transport are crucial for osmoregulation.
- Bicarbonate (HCO3-) secretion plays a role in marine teleost osmoregulation.
Purpose of the Study:
- To compare intestinal bicarbonate secretion across different fish groups.
- To investigate the role of Cl-/HCO3- exchange in chondrichthyan and chondrostean fishes.
- To determine if intestinal bicarbonate secretion is a conserved osmoregulatory mechanism in fish.
Main Methods:
- Comparative analysis of intestinal fluid composition in Gulf toadfish, Siberian sturgeon, and bamboo shark.
- Measurement of luminal ion concentrations under hyperosmotic conditions.
- Analysis of published data for cyclostome Lampetra fluviatilis.
Main Results:
- All tested species exhibited a 10-fold increase in luminal HCO3- concentrations compared to plasma levels.
- HCO3- was concentrated up to 50 times ambient seawater levels due to intestinal secretion.
- Reduced luminal Cl- suggests Cl-/HCO3- exchange is active in sturgeon and sharks.
- Sturgeon precipitated gut carbonates, a mechanism for reducing osmolality and maintaining calcium homeostasis.
Conclusions:
- Intestinal HCO3- secretion is a conserved osmoregulatory strategy across teleost, chondrostean, and chondrichthyan fishes.
- Intestinal Cl-/HCO3- exchange is integral to hydromineral balance in all fish drinking seawater.
- This mechanism likely extends to cyclostomes and potentially other marine animals.
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