Aquaculture animals means fish, aquatic crustaceans and molluscs (including shell-fish / mussels) at any stage of development (incl. gametes, eggs, semen), even those from the wild intended for a farm.
Different conditions apply to import up to 5 aquaculture animals as pets:

Bringing pets to Switzerland

For ornamental fishes not considered as pet animals see

Ornamental fish, crustaceans and molluscs from third countries

CAVE:
Imports of all species that could threaten the native fauna are prohibited. They are listed in annex 3 of the "Verordnung zum Bundesgesetz über die Fischerei" , see Federal law and ordonnances regarding fishery (in German).

Regulations - permit

All information included in the following documents has to be studied with attention and all requirements to be met – it will help avoiding troubles at the point of entry (customs):

General rules for imports from third countries (version of January 1st. 2008)
Last modification: 14.01.2008 | Size: 36 kb | Type: PDF

Import and transit of live animals from third countries
Last modification: 01.07.2008 | Size: 42 kb | Type: PDF

Border veterinary checks

Supplementary specific requirements on importing aquaculture animals from third countries:

Importing aquaculture animals from third countries
Last modification: 04.07.2007 | Size: 31 kb | Type: PDF

Einfuhrgesuch für lebende Fische, Fischeier und Fischsamen sowie Süsswasserkrebse (94/42b) (in German)
Last modification: 13.08.2007 | Size: 65 kb | Type: PDF

Zusammenfassung der fischereirechtlichen Bestimmungen (in German)
Last modification: 15.01.2007 | Size: 24 kb | Type: PDF

Details, approved countries of origin and models of the prescribed veterinary certificates

Please read with attention the exact animal health requirements depending on the country of origin and the intended use (e.g. farming, restocking, further processing before human consumption) - laws on fisheries see above.