Respiration
Ventilation rate
Individual-level metric of respiratory effort
What the evidence says
During active ventilation, salmon generate water flow across the gills through coordinated mouth and opercular pumping.
Ventilation rate generally increases with metabolic demand, but can be confounded by ram ventilation.
Ram ventilation is an alternative respiration strategy utilized when swimming or current speeds push sufficient water over the gills without need for active pumping. Instead, the mouth is held open during ram ventilation.
How to score the indicator
Scoring guidelines
- Ventilation rate (mouth or operculum) is the frequency of open/close movement cycles.
- For each individual in the video footage, the number of open/close movement cycles is counted for as long as the mouth or operculum are clearly visible.
- Ventilation rate is calculated as the number of open/close cycles observed divided by the duration of observation.
- Observation duration should be a minimum of 5 seconds.
- Accuracy of group-level estimates will improve with larger sample sizes, ideally 30 or more fish.
Video library
Interpretation
- Mouth and opercula movement are strongly and directly correlated.
Modulating factors
Body size ▼ Decreases frequency
Ventilation frequency decreases with increasing body size.
Dissolved oxygen ▼ Decreases frequency
Greater dissolved oxygen availability reduces the need for ventilation across all size classes.
Salinity ◆ No effect
No discernable change in ventilation frequency with salinity.
Current speed ▲ Increases frequency
Only a minor increase in ventilation rate in 160g fish between 0.25 and 2.2 body lengths per second with high (> 90%) dissolved oxygen saturation. 
Acute stressor (flashing) ▲ Increases frequency
Acute stressors, such as flashing light, increase ventilation frequency.
What remains unknown
How the point of onset of ram ventilation varies with body size and current speed (relative and absolute)
How does maximum ventilation rate vary with body size? Temperature?