A prawn penny is an item released with Aquariums. It is a possible reward from opening a prawn ball (25% chance). It is a temporary item that lasts for 25 fish, and it increases the chance of finding a golden fish egg. The length can be doubled by unlocking the Tier 3 Prawn Perks at the Prawnbroker.
Pennies and pounds may be activated up to a total of 1000 charges. If you attempt to activate any bringing you over the maximum, you get a message "You cannot add that many charges at this time (X/1000 charges)." X is the number of charges you currently have.
Prawn penny and pound charges are consumed whenever a fish with an associated golden fish egg is caught, even if that fish egg is already found and cannot be obtained again.