Tapfish is basically Farmville, except you grow fish in a virtual aquarium instead of crops on a virtual farm.
The idea is simple: you have tanks where you purchase and breed different fish, tropical, exotic, and more. You buy fish eggs to "hatch" into fish, and you then feed them periodically, keep the tank clean, and occasionally breed some interesting hybrids. There are two currencies: fish coins, and fish bucks. Clearly some fishies cost more than others. Some fish can even run a profit if you grow them, so basically the idea is to start with the starter fish and breed your way to specials and exotic fish. (And you can have multiple tanks)
Different fish mature at different rates. Some may even take a several days to mature. At least nobody can steal your fish here.
Animation is rather minimal, and the fish is a bit small to be interesting. Still, the fun of "breeding" different fish to make hybrids and a bit of virtual pet thrown in makes for an interesting occasional diversion.
You can also use micro-transactions to buy more fishbucks and fishcoins, or use the various "trial offers" to get more fishmoney. It's an interesting incentive to push you to get more stuff. They study the reward schedule very well. It can be quite addictive.
Supplemental information: after longer play, the evilness of the app starts to come out. You are encouraged to clean and "love" other people's fish as well, and that earns you fish coins. Nothing wrong with that. So the idea is you form groups of other TapFish player and do a love/clean circle. Eeek.
All of the advanced features (more exotic fish, decorations, etc.) require fishbucks, which can ONLY be obtained by download and trying apps, or pay real $$$ via microtransactions. And without access to more tanks and more advanced fish types, your breeding program will be forever limited and slow. Only 2 species can be bred at one time without pay fishbucks). Breedable species is limited to about half dozen without fishbucks either.
You also need to check your tank every few hours else your fish may die, and require fishbucks to revive (else, flush it virtually).
There are a TON of decorations, all requiring fishbucks or several THOUSAND coins. When typical "profit" from a normal fish is only like 20-30 coins and that takes a day or two to grow up, it's clear you need to pay $$$ to "enjoy" this game.
Rating: Try it