The osmorespiratory compromise in the fish gill

Area of Science:

• Physiology
• Comparative Biology
• Aquatic Respiration

Background:

• August Krogh's discoveries highlighted fish gill functions in gas exchange and osmo/iono-regulation.
• The osmorespiratory compromise describes a trade-off between these two gill functions.
• This concept is now understood to be more complex than initially proposed.

Purpose of the Study:

• To explore the complexity of the osmorespiratory compromise in fish gills.
• To detail the mechanisms fish use to dynamically regulate this compromise.
• To understand how these mechanisms facilitate decoupling of ion/water fluxes from oxygen uptake.

Main Methods:

• Review of known mechanisms for altering gill functional surface area and diffusion distance.
• Identification of blood flow pathway reorganization strategies.
• Analysis of reversible gill remodeling processes.

Main Results:

• At least six mechanisms exist to modify gill structure and function.
• These include blood flow redistribution and reversible gill remodeling (e.g., cell proliferation).
• These mechanisms allow dynamic regulation, decoupling ion/water fluxes from oxygen uptake during exercise and hypoxia.

Conclusions:

• Fish gills possess sophisticated mechanisms to manage the osmorespiratory compromise.
• Hypoxia-tolerant species can reduce ion/water fluxes even during hyperventilation.
• The intensified osmorespiratory conflict in marine fish warrants further investigation.