I stopped labelling tanks and had a Sheet on the wall. Each tank was numbered and the fish names where on the wall with their prices and a little information about them and the tank they were in.I was being hypothetical
And speaking from what I have seen in the past when visiting pet shops that have fish and seeing the poor blighter having to label the aquariums (for ID and pricing) and struggling to get the generic names (and pen names etc) of fish not just onto the label but spelt correctly too