Fish For Five Gallon Tanks
If you've purchased a tank that's only five gallons, be prepared for a great deal of frustration and 'down the nose' looking as people inform you that it is far too small for a fish. Lots of little tanks are sold under the guise of being goldfish bowls, which they most certainly are not. Goldfish are messy critters that need room. There are however, some very pretty and entertaining fish that you can keep in a five gallon aquarium.
These fish are tropical, so you will need a heater to keep the water temperature in the aquarium steady. Don't be put off by the idea of tropical fish, tropical fish are popular for a reason. They are beautiful to look at and you can fit far more tropical fish in a tank than you can cold water fish.
I have two recommendations for a five gallon tank today, depending on what kind of fish keeper you want to be. If you want to create a delightful little underwater planted paradise for your fish, you can take a five gallon tank, add some peat for plant growth, put some plants in it, cover the peat with a nice grave substrate and put a few neon tetras in the tank. Add a little lighting over the top of the tank and it will be very pretty indeed! You'll need to run a filter to keep neons happy, but a small school of four or five little neon tetras will do very well in a planted tank, and these planted nano tanks as people call them, are very popular in the hobby.
On the other hand, if you can't be bothered with all the expense and maintenance of creating a planted tank, a five gallon is the perfect size for a single fighting fish. Fighting fish do best on their own, and can be kept in either filtered or unfiltered tanks. If you don't filter the tank, you will need to completely clean out the tank and everything in it with hot water at least once a week. If you do choose to filter the tank, occasional water changes are all you'll need to do. I'd personally recommend running a filter if at all possible as it cuts down on the work you have to do and minimizes the stress your fish will feel being yanked out of its tank every week for cleaning.
There you have two suggestions for five gallon tanks that aren't remotely cruel to the fish in them and that will keep your fish and you happy for the duration of their natural lives.