Fish that do not need filters

Although I don't advocate that beginners keep fish without filters, many fish have been kept in ponds and containers without filtration for over 4,000 years. There are many hobbyists who keep natural planted filterless tanks. Many cichlid breeders/importers in Africa use concrete ponds with large (90%) water changes once or more per day. Also true in some Asian facilities. My reef tank is just live rock, live sand and water pumps for circulation. It can and has been done, it just requires GREAT diligence and experience. Again, NOT for the beginning hobbyist!
 
It also depends on the gallons of water you are talking about. Much more manageable with a pond as opposed to a small aquarium or bowl.
 
what about some goldfish (with proper cleaning of course!) is it possible to keep just one goldfish in a fish bowl?
 
My reef tank is just live rock, live sand and water pumps for circulation. It can and has been done, it just requires GREAT diligence and experience. Again, NOT for the beginning hobbyist!

In a reef tank, your live rock and live sand is the filtration system.

From Wiki on the purpose of live rock:
"For the aquarium trade this rock is highly valued not only for the diversity of life it can bring to the closed marine environment, but its function as a superior biological filter that hosts both aerobic and anaerobic nutrifying bacteria required for the nitrogen cycle that processes waste. Live rock becomes the main biological nitrification base or biological filter of a saltwater aquarium."
http://en.wikipedia.org/wiki/Live_rock
 
Dead fish don't need filters!

To keep fish alive in an enclosed system, a filter is needed to remove waste (and maintained). That's why us humans have sewage systems!
 
having a fish without a filter, any fish, is like never flushing your own toilet and trying to live...
 
AquariaCentral.com