What fish can you keep without a filter?

Here's why:

* Waste buildup: Fish produce waste (ammonia, nitrite, and nitrates) that can quickly pollute the water and become toxic if not removed.

* Oxygen depletion: Fish need oxygen to survive, and without a filter, the water can become oxygen-depleted, especially in small tanks.

* Disease: Bacteria and parasites can thrive in dirty water, increasing the risk of your fish getting sick.

There are a few exceptions where you *might* be able to keep fish without a filter for a very short time:

* Very small tanks: Some people keep tiny shrimp or snails in tiny bowls or jars with no filter. This is extremely risky and requires constant water changes to maintain a safe environment.

* "Temporary" setups: If you're transporting fish or setting up a new tank, you can use a small airstone for oxygenation and do very frequent water changes. This should only be for a few days at most.

It's always best to consult with a knowledgeable pet store employee or aquarium expert before setting up any fish tank. They can advise you on the proper filter system for your chosen fish and tank size.