Insaniquarium may not be the most top-of-mind retro title, but it's a fun, casual title with tons of fish. The game is a combination of puzzles and resource management. Players must manage money and food resources to keep the guppies alive.
Bosses come periodically to eat the guppies, so players must fend off the boss and protect as many fish as possible. If you're looking for a retro title you can play in short bursts, Insaniquarium is it.
Buy Insaniquarium on Steam for $4.99.