The development of cannibalism of northern pike(Esox lucius)larvae was studied under controlled conditions. Pike larvae were reared in six glass, 50–1 aquaria at three stocking densities: 440, 2 200 and 4 400 larvae per aquarium. Fish were fedad libitumwithArtemianauplii and sieved Zooplankton. After 4, 8 or 12 days of rearing, pike larvae were anaesthetised and measured for total length (TL) and body weight (BW). Lowest survival and fish size were noted at the highest stocking density. The frequency of all cannibalistic attacks decreased in the order: highest > middle > lowest density; the frequency of successful attacks (expressed as the number of injured sibling fish) decreased, however, in opposite order.