The influence of bulk and trace metals on the circadian rhythm of heart rates in freshwater crayfish, Astacus astacus

The freshwater crayfish Astacus astacus is a nocturnal species known to express circadian rhythmicity in heart rate. With the aid of a Computer Aided Physiological MONitoring (CAPMON) system, the influence of potential hazards, such as trace metals, on the expression of circadian rhythmicity in heart rate was investigated. Effects of variations in salinity on circadian rhythmicity in heart rate were also investigated, since heart rates are known to be affected by such changes in some estuarine crustaceans. The influence of Hg2+, Cu2+ and NaCl on light driven (12:12 h, light:dark regime) circadian rhythmicity in heart rate was examined. Exposure to 0.1 mg Hg l−1 invariably increased heart rate by increasing heart rate during day time. This eventually resulted first in loss of rhythmicity and ultimately in death. The response to 8.0 mg Cu l−1 seemed more complex with great inter-individual variation, involving increases as well as decreases in both day and night time heart rates. An increase in salinity from 0.09 m NaCl to 24.0 m NaCl seemed to decrease the expression of circadian rhythmicity in heart rate, primarily because heart rates remained low during the night. From the present experiments it appears that the presence of trace and bulk metals in the surrounding media influences the expression of circadian rhythmicity of heart rates in the crayfish A. astacus.