Abstract We used broad, shallow and deep, narrow aquarium tanks to examine the behavioural responses of Antarctic krill to photosynthetically active radiation (PAR) and ultraviolet (UV) radiation. Groups of animals were exposed to different levels of radiation and to gradients of radiation and their mean position in the tanks were recorded photographically. Results from the horizontal tank (length 2.4 m) showed that krill moved from areas of high levels (7 W m −2) of UVA exposure (320–400 nm) to areas of low exposure (0.1 W m −2), differing in irradiance by two orders of magnitude. In addition, a similar reaction was observed in krill exposed to a PAR gradient of similar magnitude (30–5 W m −2). There was no observed reaction to UVB wavelengths (280–320 nm). Krill in the vertical tank (height 1.5 m) remained evenly distributed throughout the tank when exposed to both high and low levels of PAR. Additional exposure to UVA wavelengths from the surface caused krill to increase their depth in the tank significantly, to areas of lower irradiance. Addition of UVB radiation had no effect on the mean depth of krill in the tank. The implications of these findings are that krill may avoid regions of high UVA or PAR and consequently would reduce their exposure to UVB and therefore the risk of UVB-induced damage, such as disruption to DNA.