Parasites as indicators of the movements of deep-sea fish
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 and 5,000
metres.
In these adverse conditions of cold temperatures, darkness and high pressures lives an active community of animals. The rat-tail (Coryphaenoides armatus) is a large and abundant member of this community and may be up to a metre long and 5 kg 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.
Graph of host-parasite distributions with depth.
Parasites can be utilised as 'biological tags' to track fish movements. The rat-tail 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.
For further information contact: Rod Bray