Schooling behavior of Antarctic krill (Euphausia superba) in laboratory aquaria: Reactions to chemical and visual stimuli

Antarctic krill,Euphausia superba, often exhibit abnormal behavior in laboratory aquaria, usually hovering in a stationary position, unresponsive to most external stimuli. In the austral summer of 1985–1986 at Palmer Station on Anvers Island, Antarctica, we provided laboratory conditions which inducedE. superba to school in large aquaria. Captive krill swam horizontally and exhibited the full spectrum of behaviors normally displayed while schooling at sea. Schooling krill avoided visually contrasting stimuli, with avoidance distances correlated with stimulus size. Schools responded in qualitatively different ways to presentations of food, chemical compounds, and abrupt increases in light intensity. We describe the conditions necessary for aquarium schooling and discuss the importance of an appropriate social environment for displays of escape, avoidance, and feeding behaviors and of positional preference within the school.