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Large scale introductions of fish species into areas outside their native range is a comparatively recent phenomenon. Some transfers of fish nay be considered ancient, in that they date from the middle ages in Europe but the majority of such movements date from the end of the last century. The detrimental effects of some introductions soon became apparent, but until recently were insufficient to cause widespread concern. However, with the development and spread of aqua-culture and an increasing public awareness of the environment fears of the impacts of introductions of fish species have grown. This lead the International Council for the Exploration of the Sea (ICES) to form a Working Group on the introduction and Transfer of Marine Organisms which formulated a Code of Practice which was adopted by ICES in 1973. The International Consultation on Fishery Resources Allocation (Vichy, France, 1980) and the Eleventh Session of the European Inland Fisheries Advisory Commission (EIFAC) held during 1980 both recommended that the procedures for introducing fish species into freshwaters be reviewed. As a result EIFAC adopted a Code of Practice based on the ICES model at its Fourteenth Session (Bordeaux, France, 1987). All other FAO Regional Fishery Bodies dealing with inland waters have also expressed their concern about introductions at their sessions and are currently investigating the relevance of the ICES/EIFAC Code to their own situations.

The development of the Codes of Practice also involved the framing of definitions relating to the Code which are followed in this volume:

Introduced species (Includes both non-indigenous and exotic species): Any species intentionally or accidentally transported and released by man into an environment outside its present range.

Transferred species (includes transplanted species): Any species intentionally or accidentally transported and released within its present range.

Transfers are usually intended to support stressed populations, introduce genetic diversity into a stock or to reestablish a species whose stocks have failed locally. Introductions are intended to insert a totally new element into the fauna.

One reservation is made with respect to these definitions in that a species is considered to have been introduced to a country once it has crossed national boundaries. This means that species are included in the listing if they are transported into a country as part of current commercial practice for food or ornament and not for stocking into natural environments. Experience has shown that even such species may have impacts through the release of pathogens or through escape.

This volume deals primarily with international introductions and generally excludes the many more introductions made between river basins within national territories. It is recognized that this distinction does not appear consistent ecologically because movements of species say from the Eastern to the Western drainages of the Soviet Union or the United States may be far more significant than an introduction from Netherlands to Germany. This limitation of scope may be justified however, in that the number of intranational introductions is so large as to defy the kind of listing made in this document. Furthermore passage over political frontiers poses problems of planning and legislation that differ in complexity from those facing a single nation seeking to regulate movements of species within its own frontiers.

The development of Codes of Practice and protocols for considering and carrying out introductions has been accompanied by the collection of data on the introductions that have actually been carried out. This information has been collected not only from literature but also in response to requests for information circulated to member countries of FAO. These replies resulted in the publication of a Register of International Transfers of Inland Fish Species (Welcomme, 1981) and additions and corrections to that document are included in the present volume which now presents a synthesis of information provided by scientists and fishery administrators from 140 countries. The nature of much of the information contributed makes direct referencing of many of the entries difficult and for those wishing to deepen their knowledge of this topic more complete bibliographies exist, e.g. Rosenthal (1978).

A database such as this can never be complete and much information is still lacking in several areas. For instance, the listing of introductions into the OSSR is far from complete and many invertebrate introductions, such as those of the Mysidaceae, into the waters of the USA and USSR to enhance fish food production, are not included. It is intended that the database be updated and to this end it would be greatly appreciated if all readers communicate any additional information relating to transfers of Inland aquatic species to: R.L. Welcomme, Senior Fishery Resources Officer, FAO, Via delle Terme di Caracalla, 00100 Rome.

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