Development of a feeding behavioural bioassay using the freshwater amphipod Gammarus pulex and the Multispecies Freshwater Biomonitor

The present study reports the development of a feeding behavioural bioassay using the Multispecies Freshwater Biomonitor (MFB). This device is based on the quadruple impedance conversion technique to record online different behaviours of animals. Animal movements in the water generate specific frequencies, and the MFB can estimate the percentage of time producing each frequency (from 0.5 to 8.5 Hz) by means of a stepwise discrete Fourier transformation. Two feeding behavioural bioassays were conducted in order to know the frequencies related to feeding behaviour of the freshwater amphipod Gammarus pulex. The first bioassay assessed the effects of food presence in the amphipod behaviour. The second bioassay assessed the effects of cadmium on the feeding activity (measured as leaf weight loss) and behaviour (swimming, ventilation, and feeding recorded through the MFB) of G. pulex in order to check the suitability of the developed method. The results of the first bioassay showed that the frequencies ranging from 3.0 to 4.5 Hz were highly correlated with feeding activity, especially 3.5 and 4.0 Hz. In the second bioassay, we found that cadmium reduced feeding and ventilation behaviours. Our study showed that the MFB can be used to record the feeding behaviour of G. pulex exposed to toxicants. The developed feeding behavioural bioassay allows an accurate and automatic assessment of several endpoints, including feeding, swimming and ventilation. However, the study of the complex behaviour of G. pulex using the MFB needs further research, since some behaviours seem to generate similar frequencies.