Continuous video-based observation of locomotor activity in wild-caught river lamprey Lampetra fluviatilis

The study evaluated whether continuous operator-free video monitoring can characterize individual 24-h locomotor activity profiles in wild-caught Lampetra fluviatilis. We used continuous operator-free video monitoring to characterize locomotor activity in four wild-caught river lampreys from Orzega River. Individuals differed in total length, from 3.4 to 11.6 cm, and were recorded individually and continuously under low illumination (<1 lx) for 69 h. Locomotor activity was estimated as normalized hourly activity. Although total active time differed among individuals, locomotor activity was generally concentrated during the operational evening–morning interval (20:25–08:25, GMT +3). Significant interdaily consistency of hourly locomotor activity profiles was detected in three of four individuals, and cosinor analysis supported a 24-h rhythmic component, with acrophases occurring within the evening–morning interval in all individuals. Temporal overlap, defined as simultaneous activity of two or more independently housed lampreys, was highest from late evening to early morning. These preliminary individual-level observations of four wild-caught individuals under the field-station conditions are consistent with previous studies reporting predominantly nocturnal or low-light-associated locomotor activity in lampreys. The study suggests that continuous operator-free video monitoring can provide individual-level information when only a few wild-caught lampreys are available, which may be relevant for low-disturbance studies of freshwater populations.