Animal Protection Act regarding fish
IMPORTANT! To calculate the minimum volumes for aquariums, multiply the current body length of the fish by the corresponding number of litres and the number of fish for each size class. The minimum volume in litres is the sum of the products for each size class. For a correct calculation of your fish population, we recommend the VZFS calculator (page in German).
https://www.vzfs.ch/de/fischbesatzrechner