Abstract

We know o f many examples of the danger of introducing foreign organisms into areas where man has already caused unbalanced conditions in nature. Very few countries allow unrestricted introduction of plants, fruit, insects, etc. This fear is indeed valid and is supported by numerous cases of crop pests and irreparable damage to major natural resources. The uncontrolled transfer of crayfish may not only introduce new crayfish parasites which can seriously harm other animals, including man, but crayfish may also be vectors for fish parasites such as viruses. Thirdly, harmless commensals or parasites on the crayfish may become aggressive to that same crayfish or to other animals in the new environment. Finally, the new crayfish might become a pest itself. It should also be remembered that the damage to an organism by a new parasite is a damage to the balance in the environment, to predators of the organisms, to its food, etc. It is our responsibility as specialists to warn political and fishery officials of the risks in relation to the benefits, and they must rely on our judgment.

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