| Summary: | The behaviour of planktonic animals remains poorly understood due to the difficulty of observing them in situ without influencing their behaviour. Here we review experiments on the behavioural responses of Northern krill, Meganyctiphanes norvegica (and related organisms), in isolation in laboratory-based aquaria. The value of this approach lies in the close observation that is possible; the downside is the uncertainty as to how well the observed behaviour relates to the natural behaviour of the subject animal. We discuss studies of swimming and swarming, and the responses of krill to light. We consider techniques involving automatic recordings that avoid, to some extent, making subjective decisions on behaviour. The effects of isolation of such a gregarious animal and of exposure to unnaturally high light levels are also considered. We conclude that such experiments can be of great value as long as these limiting factors are addressed.
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