Effects of Cadmium on Locomotor Activity Rhythms of the Amphipod Gammarus aequicauda

Gammarus aequicauda exhibited 90.2±0.4% of its total daily activity at night under a light-to-dark cycle.

• The amphipod G. aequicauda maintained a strict nocturnal rhythm, confirming its behavioral pattern under a 12:12 light cycle.
• Circadian rhythms persisted for 10 days in constant darkness, with a mean periodicity of 24.32 hours, indicating endogenous control.
• Exposure to sublethal concentrations of cadmium (Cd) did not alter the nocturnal activity patterns of G. aequicauda.
• Significant decreases in swimming activity during the night were observed at Cd concentrations of 0.24 and 0.28 mg l(-1).
• Locomotor activity bioassays with G. aequicauda may serve as sensitive indicators of Cd contamination.
• Sensitivity and tolerance to Cd in short-term bioassays may be influenced by the timing of the tests.

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