How many fish can be happy in a 37 gallon tank?

The number of fish that can be happy in a 37 gallon tank depends on several factors, including the size of the fish, their activity level, and their compatibility with each other. It's always better to err on the side of caution and stock the tank with fewer fish rather than overcrowding it.

As a general rule, an aquarium that is 3 feet long, 1 foot wide, and 2 feet high (which holds about 37 gallons of water) can comfortably accommodate:

- A single medium-sized fish, such as a Betta or Gourami, along with a few smaller schooling fish like Neon Tetras or Cardinal Tetras (around 10-12 of them).

- A community of several smaller species of fish, such as Guppies, Platies, or Mollies (around 15-20 of them, depending on the species).

- Several Corydoras catfish species, which are bottom dwellers and help clean the tank (around 6-8 of them).

Remember, these are just rough estimates, and the actual number of fish you can keep in a 37 gallon tank may vary depending on the specific species you choose, their temperaments, and other factors such as filtration and aeration. It's important to research the specific needs of the fish you're considering to make sure they're compatible with each other and with the conditions in your tank.