More than two thirds of the world's surface is covered by sea and 60 per cent of that lies between depths of 2,000 metres and 5,000 metres.
In these adverse conditions of cold temperatures, darkness and high pressures lives an active community of animals. The rattail (Coryphaenoides armatus) is a large and abundant member of this community and may be up a metre long and 5 kilogrammes in weight. In the North Atlantic Basin rattails are widespread at depths of 2,100 to 5,440 metres and descend towards deeper water as they grow.
Parasites can be utilised as 'biological tags' to track fish movements. The rattail harbours parasitic worms, which pass through a series of unrelated hosts in their life cycle. The different distributions of these host species mean that this fish cannot acquire a given parasite infection throughout the whole of its range. It may acquire a parasite and carry it to a region where the intermediate host does not occur. The parasite then acts as a 'tag', indicating the past movements of the individual fish. This technique has particular value in deeper waters, where standard tagging and recapture methods are precluded by the impossibility of bringing the trawled fish to the surface alive. The percentage occurrence of a parasitic flatworm in the rattail at various depths in the deep sea off the southwestern coast of Ireland (not to scale) is shown above.
Illustrations
For further information contact:
Dr. Rod Bray,
The Natural History Museum,
Cromwell Road, London, SW7 5BD, UK
Tel: +44 (0) 171 938 9492 Fax: +44 (0) 171 938 8754
E-mail: Rod Bray rab@nhm.ac.uk
