The Fish Emporium sells various things for your Virtual Tank. There are 8 slots total, with one dedicated to tank backdrops and another dedicated to Virtual Tank Upgrades. The mermaid restocks each day, so you can only buy the 1 thing showing in that slot each day (it doesn't get replaced the same day). Slots A-D are more or less constant..
Slot A
A plain guppy costs 25 shells. You can buy 1 each day. These guppies will never be eaten by anything else. Try naming one Santa .
Slot B
A plain Carnivore costs 100 shells. They eat guppies from the "Feed" button in the Virtual Tank. They won't eat anything store-bought.
Slot C
A colorful guppy is extra special, so it costs 500 shells. Why is it special? Because it's so pretty. The colors vary from day to day. It eats the same amount of food and gives you the same number of shells as a regular guppy, it's just prettier.
Slot D
Similarly, a colorful Carnivore costs 1,000 shells. The colors vary from day-to-day. Same food, same shells as the plain carnivore.
Slot E
A semi-rare fish
Slot F
A fish with special properties
Upgrade Slot
The virtual tank upgrades, followed by a fish with special properties.
Backdrop Slot
Various backdrops can be purchased for 15,000 shells..