Fermi Problem Friday

Enrico Fermi was famous for his pioneering work in atomic theory. He won the Nobel Prize for his work on radioactivity with neutrons that subsequently led to the discovery of nuclear fission. Fermi posed a certain type of question, now called a Fermi Problem. The solution of which is impossible to determine an exactly but can be approximated by deductive "thinking outside the box" reasoning.
The classic example is "How many piano tuners are there in Chicago?" While this may seem impossible at first, you can estimate the solution through a series of steps. You can estimate how many people live in Chicago. Then guess what percentage of those people own pianos. Pianos need to be tuned after so many years. Finally putting all together, you can reasonably estimate how many piano tuners there are in Chicago.

Every Friday we hope to pose a new Fermi Problem and get your solutions. Along with your solution, send your reasoning. Feel free to be creative (that's the point).

The Problem:
How many Swedish Fish will fit into a 10 gallon fish tank?
Bonus question: How many can you fit in your mouth at once? Yum!