Does ammonia trigger hyperventilation in the elasmobranch, Squalus acanthias suckleyi?

Area of Science:

• Marine Biology
• Comparative Physiology
• Environmental Toxicology

Background:

• Ammonia is a metabolic waste product that can be toxic at elevated levels.
• Fish possess various mechanisms to excrete ammonia, but its physiological effects are not fully understood.
• The spiny dogfish (Squalus acanthias) is a relevant model for studying fish respiratory physiology.

Purpose of the Study:

• To investigate the ventilatory responses of spiny dogfish to internal and environmental ammonia.
• To determine the relationship between plasma ammonia levels and ventilation parameters.
• To differentiate the effects of internal versus environmental ammonia exposure on fish respiration.

Main Methods:

• Spiny dogfish were subjected to intravenous injections of ammonia solutions (NH4HCO3, (NH4)2SO4) and sodium salt controls.
• Ventilatory frequency and amplitude were measured using arterial catheters.
• Arterial blood gases (PaCO2), pHa, and plasma total ammonia concentration ([TAmm]a) were analyzed.
• Sharks were also exposed to high environmental ammonia concentrations (NH4HCO3).

Main Results:

• Intravenous ammonia injection significantly increased plasma ammonia concentration, leading to increased ventilation amplitude and, to a lesser extent, frequency.
• Ammonium sulfate ((NH4)2SO4) caused a greater increase in ventilation amplitude than ammonium bicarbonate (NH4HCO3).
• Environmental ammonia exposure did not affect ventilation until plasma ammonia levels rose, at which point ventilation amplitude increased.

Conclusions:

• Internal ammonia directly stimulates ventilation in spiny dogfish, primarily affecting stroke volume (amplitude).
• Ventilation frequency is more influenced by changes in blood pH rather than ammonia levels.
• Environmental ammonia must be absorbed into the bloodstream to elicit a ventilatory response in this species.