Reptilia < Fishes > Migration in the sea — oceanodromous species
Migration in freshwater — potamodromous species
Migration between fresh- and saltwater — diadromous species

4.3.4 — Pisces

You fish people are very skilful in getting these fish into cans. Cannot you be just as skilful in getting these fish to be raised over a dam? (Comment on a public hearing on a proposal for the first dam, on the mainstream of the Columbia River, 1924; from McCully 1998, p. 41)

Though less well known and popular, fishes ("Pisces") follow birds in second place with respect to the number of migratory species. The old Linnean class of "pisces" has been substituted in modern zoology by clearly separable groups, each of which has a distinct position within Chordates. Nevertheless, they are still summarised within GROMS under the common Linnean designation of fishes ("Pisces") for practical reasons. A comprehensive database exists for fish (FishBase: Froese & Pauly 2000 FishBase is available online and as CD-ROM, and lists all known fish species, based on the catalogue of Eschmeyer (1990). The migratory status for the better-known species has been assessed according to major reviews and handbooks in cooperation with R. Froese, using FishBase 1999 (Froese & Pauly 1999). The result was integrated into both databases. In addition, GROMS contains the FishBase species code, which allows easy connection to the online version of FishBase ( The species code facilitates update, and recent changes of the latest version (Froese & Pauly 2000) were easily integrated into GROMS.

Our categorisation of fish migration behaviour follows McDowall (1988), and has been summarised in chapter 2. We differentiate between migrations entirely within freshwater (potamodromous and limnodromous), marine environments (oceanodromous), or between sea- and freshwater (diadromous). This differentiation is now well-established among fish biologists, but certainly does not cover the entire complexity of the phenomenon. Most fish migrations take place to find a suitable spawning area, others are for obtaining food or avoiding predation. Some fish migrate seasonally to take advantage of favourable climatic conditions. There are two types of return migrations: a to-and-from migration, by retracing the journey, and a loop or circular migration (Baker 1978). There might even be combinations, such as certain races of the Pacific salmon (Oncorhynchus tshawytscha). They descend their natal stream, migrate circularly within the ocean, and then as adults move up the home stream in an opposite direction (McKeown 1984). This means that periodicity of migration differs between individuals and the species: There might be an annual fish migration, but individuals might need several years or even their entire life to complete the cycle. As for other migratory species, these detailed patterns often vary among distinct stocks. An adequate record of these complexities within the database would require very precise maps with timecodes for different stocks and age classes, and a corresponding extension of the geo-database model.

At present, only sturgeons (Acipenseridae) have been mapped (Figures 84, 85). These maps are based on distribution data compiled by the German government (Federal Republic of Germany 1999).
A major set of distribution maps for economically important marine species was published in the FAO "Atlas of the living resources of the seas" (FAO 1981). It includes both diadromous and oceanodromous species, and contains detailed maps of the bathymetric and seasonal distribution of stocks.
Reliable information on a recent edition of the atlas could not be obtained, but we suppose that the data are available in digital format, at least for government agencies and official bodies.

For the time being, we had to concentrate on the identification and rough classification of migratory fish species. Even so, considerable knowledge gaps were detected for fish migrations in tropical river systems. Some excellent case studies highlight the importance of this phenomenon (for the Amazon: Barthem & Goulding 1997), but comprehensive reviews are not available. The biblio-graphy is widely scattered, and an assessment of migratory status for tropical fishes had to be postponed to the next phase of the GROMS.

The summary statistics for the major migration categories and their threat status are given in Table 4.9.

Tab. 4.9: Migratory status, threat and CMS status of fishes (total of migrants: 874). The following Red List categories are summarised as "Threatened": (CR) Critically Endangered, (EN) Endangered, (VU) Vulnerable.

Note the high proportion of endangered anadromous species. Anadromous and potamodromous sturgeon species (Acipenseridae) are listed in CMS Appendix II, the whale shark (Rhincodon typus) is the only oceanodromous species listed by CMS, and the giant catfish (Pangasianodon gigas), a potamodromous migrant from South East Asia, is the only fish species listed in CMS Appendix I.

Tab. 4.9: Wanderstatus, Gefährdung und CMS-Status der Fische (Gesamtzahl der wandernden Arten: 874). Die folgenden Kategorien der Roten Liste werden als "Bedroht" zusammengefaßt: Vom Aussterben
bedroht (CR), Stark gefährdet (EN), Gefährdet (VU).

Beachten Sie die verhältnismäßig hohe Anzahl
gefährdeter anadromer Arten. Anadrome und potanadrome Stör-Arten (Acipenseridae) sind im Anhang II der Bonner Konvention gelistet, der Walhai (Rhincodon typus) ist die einzige oceanodrome Art, die von den Anhängen der Bonner Konvention erfaßt wird. Der Riesenwels (Pangasianodon gigas), ein potamodromer Wanderer aus Südostasien, wird als einzige Fischart auf Anhang I der Bonner Konvention geführt.

Migration Species Threatened Percent Extinct Data deficient CMS listed
amphidromous 69 8 12% 1 7  
anadromous 140 20 14%   14 12
catadromous 65 1 2%   1  
limnodromous 10 1 10%   1  
potamodromous 89 15 17%   6 7
oceanodromous 501 18 4%   4 1

According to the International Red List 2000, there are 801 threatened fish species, which is approximately 3% of the ~25,000 fish species. But for freshwater species, this percentage doubles to 6% (600 of ~10,000 freshwater species), indicating the manifold threats to freshwater ecosystems. The percentage is even higher for freshwater migrants (limnodromous: 10%, potamodromous: 17%), as well as for species using freshwater for spawning (amphidromous: 12%, anadromous: 14%). These numbers clearly reflect the disastrous destruction of spawning grounds for migrants by dam construction (see section 4.2).

The International Red List 2000 lists 81 extinct fish species (0.5%), which is higher than among
migratory fish species, where "only" 1 species, the New Zealand grayling, has gone definitely extinct (0.1%). However, there are two stocks of anadromous sturgeons listed as extinct: the Adriatic Sea population of the giant sturgeon (Huso huso), and the Aral Sea stock of the barbel sea sturgeon. Note that there is a considerable number of species listed as "Data Deficient" by the International Red List 2000 (Hilton-Taylor 2000).

Reptilia < Fishes > Migration in the sea — oceanodromous species
Migration in freshwater — potamodromous species
Migration between fresh- and saltwater — diadromous species

This document should be quoted as part of the publication "Riede, K. (2001): The Global Register of Migratory Species ­ Database, GIS Maps and Threat Analysis. Münster (Landwirtschaftsverlag), 400 pp." + CD

 by Klaus Riede