Method for obtaining reliable R-waves in fish electrocardiograms by utilizing conductivity of seawater

Area of Science:

• Aquatic biology
• Bioelectrical signal analysis
• Fish ecophysiology

Background:

• Managing farmed fish health and understanding wild fish ecophysiology requires effective bioelectric signal measurement.
• A previous method used a single internal electrode and a seawater external electrode but struggled to reliably detect R-waves in fish electrocardiograms (ECGs).

Purpose of the Study:

• To investigate optimizing the internal electrode placement for reliable R-wave detection in fish ECGs.
• To explore the feasibility of simultaneously measuring ECGs from multiple fish using the improved method.

Main Methods:

• Experimentally determined optimal insertion points for a specialized internal electrode in four fish species (approx. 10 cm length).
• Evaluated the ability to capture fish ECGs with R-waves by adjusting internal electrode position relative to the heart.
• Assessed simultaneous ECG measurement of multiple fish using a single common external electrode.

Main Results:

• Reliable R-waves were observed in fish ECGs when the internal electrode was inserted near the heart across different species.
• Simultaneous ECGs with detectable R-waves were successfully recorded from three fish using a single common external electrode.
• The optimized method demonstrated a reduction in the total number of bioelectrodes required for multi-fish ECG measurements.

Conclusions:

• Optimizing internal electrode placement near the heart is crucial for obtaining reliable fish ECG R-waves using the novel method.
• The technique shows promise for simultaneous multi-fish ECG monitoring, offering advantages in electrode reduction.
• This advancement supports improved fish health management and ecophysiological research.