The short answer is no. All fish need a filter to thrive inside their aquariums. They will survive for some time, but you’ll need to do extra water changes and cleaning. The tank’s overall maintenance will be more in-depth and more often rather than if you had a filter to take care of your fish.
Filters go through many different filtration processes. These processes will ensure that you fish and the water remain clean, clear, and healthy. Fish naturally produce toxins that are harmful to them, and, over time, fish waste and leftover food will visibly dirty the tank. Algae will grow on the decor, plants, and the sides as well. A proper filter will ensure that your fish and the tank stay healthy, and the water will be clear. Plus, you’ll only need to clean the filter once in a while instead of deep-cleaning the entire tank more often.