An Automated Interpulse Duration Assessment system (AIDA) is described which permits detection of irregularities in cardiac rhythms in selected invertebrates. The sensitivity of AIDA was demonstrated by its ability to detect handling stress in mussels (Mytilus edulis) that was not evident when measuring heart rate alone. Changes in cardiac activity patterns of crabs (Carcinus maenas) held in the laboratory for up to 10 wk was also examined using the new technique. The frequency distribution of interpulse duration changed significantly as the nutritional state changed. Potential applications of the AIDA system are discussed.

A computerised system for non-invasive monitoring of heart and ventilation rates and the time intervals between heart beats and between breaths was developed and used to investigate cardio-respiratory changes in rainbow trout exposed to hypoxia and to combined hypoxia and hypercapnia. Upon exposure to hypoxia and hypoxia-hypercapnia the arterial O2 tension decreased from about 90 mmHg to about 30 mmHg. Acid-base changes were small in hypoxia whereas exposure to combined hypoxia-hypercapnia caused a large extracellular respiratory acidosis. This acidosis was completely compensated within 24h by accumulation of bicarbonate in plasma to concentrations twice the normoxic values. The ventilation rate was increased to higher values in hypoxic-hypercapnic trout than in hypoxic trout. In contrast to previous reports, the heart rate increased in hypoxia. On top of the tachycardia response to hypoxia, the heart rate was governed by circadian rhythms, with higher heart rates during the day than during the night. The time interval between heart beats varied considerably in normoxic fish. Hypoxia strongly reduced this variability, which may originate in a reduced cholinergic tone to the heart. The width of the frequency distribution of the time intervals between breaths was not affected by hypoxia. The degree of cardio-respiratory synchronization was low in both normoxic and in hypoxic and hypoxic-hypercapnic trout.

A computer-aided monitoring system is described which permits continuous long-term recording of cardiac and respiratory activity together with locomotor activity in selected aquatic organisms. Four macroinvertebrates can be studied simultaneously using the apparatus described. However, with additional hardware (respirometry chambers, valves, oxygen electrodes and infra-red sensors), the system can readily be expanded for use with 20 or more organisms using a single computer (PC). Data are acquired using non-invasive sensors thereby subjecting test organisms to minimal stress. Examples of the type of data that have been obtained during the first 2000 h of operation are provided.

The transfer of information about distance and direction from a dancing honeybee to follower bees can be studied by means of a mechanical model of a dancing bee. The model simulates the oscillating air flows around a dancing bee. The bees are recruited by the model and follow its instructions on where to fly. The model is used for investigating the role of individual dance parameters in the transfer of information.

1.1. A computer-aided physiological monitoring system (CAPMON) is described which permits long-term, continuous recording of cardiac activity in selected crustaceans and molluscs.2.2. Infra-red phototransducers used with the system are simple to attach and allow non-invasive measurement of physiological function, thereby minimising disturbance to the test organism.3.3. Applications of the CAPMON system in pollution studies and in clinical settings with Man, are discussed.