Hello!
I am not from Basel, but I read some aquaristics forums yesterday (my husband wants aquarium...) I think people from Basel recommend: Zoo Hohl (Allschwil - near Basel), Zoo Fasler (Muttenz - near Basel), Zoo Goldfisch (Güterstrasse, Basel), Zoo Tropic (Burgfelderplatz, Basel) (
http://www.zoo-tropic.ch/), Fressnapf (
http://www.fressnapf.ch/filialen.html?kanton=basel), Qualipet (
http://www.qualipet.ch/?seite=standorte&ids=10) and I think there is also one Zoo-shop somewhere near Bahnhof in Basel.
I hope this helps