The word “krill” comes from the Norwegian language and means “whale food”. There are over 80 known krill species. In this review I will concentrate on the most common one which is Euphausia superba. Krill in the Euphausiidae family are shrimp like crustaceans that swarm in dense shoals. Krill swarms may be as dense as 10,000 animals per cubic meter of water and can stretch for kilometres. Individuals range in length from 8-70 mm, weigh up to two grams and can live for up to six years. The krill species in the Euphausiidae family are bioluminescent which means that they can produce a strong blue-green light that is probably used for communication to help them congregate the spawn. Like other crustaceans, krill have a hard calcified exoskeleton which is divided into three segments (see fig.1): the cephalon, thorax and abdomen. The head and thorax are fused into a cephalothorax. Generally the head has five segments, the thorax has eight and the tail has six. Usually each segment has a pair of appendages, but occasionally variations occur. (Campbell, 2006)