I've just been looking online for the last half hour or so at the tea brands who had cards in with the tea. Brooke Bond, PG Tips and Tetley were the main ones it seems, how widespread these went worldwide god only knows. Funnily enough there were a few examples of the types of collections they had and one which caught my eye were freshwater fish.
You can buy complete sets on line of these old cards apparently. Some sets are quite cheap too, maybe it was just selected limited edition sets that command the high prices I don't know. I feel an urge now to press forward and see if I can get a complete freshwater fish album and maybe frame it on the wall in my fish room, watch this space, lol.