An experimental aquarium for observing the schooling behaviour of Antarctic krill (Euphausia superba)

Schooling behaviour of Antarctic krill was induced repeatedly over a period of one year in the Australian Antarctic Division research aquarium. The details of the laboratory setup suitable for krill to school are described. Light intensity and food condition were found to affect krill swimming patterns and schooling behaviour. Krill swam in polarised groups and responded as a group to objects that produced sharp contrasts but not to less distinct objects. Schools broke up when they encountered dense phytoplankton patches, and aggregated more tightly when kept with a white featureless background. The diel nature of school formation was observed under simulated natural light conditions with stronger and tighter schools during daytime and no obvious schooling behaviour during night. These behavioural patterns are further discussed in terms of their costs and benefits of feeding and predation risk, in conjunction with the diel vertical migration behaviour of krill.