Food for aquarium fish and invertebrates. The copepod (Calanus finmarchicus) belongs to the Calanoid copepod family and, with its high content of O3 fatty acids and protein, is an essential energy source in the North Atlantic. The small, dried, and partially defatted crabs, approximately 2–3 mm in size, are a delicacy for fish and an indispensable plankton substitute for corals with both large and small polyps.