I went to a local pet shop in the area and found three racks full of these "bonsai" fish... People who know me know I do not care if a person is placed in such a small container. People are not my favourite living creature... But to place an animal like this, a fish, in a bowl containing less water than you drink in a can of soda, is just plain cruel.
People doing this defend their position by claiming these fish are not very mobile or active, therefore they are fine. But I disagree. Without being an expert on the subject, it is just plain common sense that this is wrong. A fish is like any system, it has inputs and outputs. Inputs being food and seawater, outputs being detritus (waste food) and ammonia expelled through the gills. Detritus breaks down into ammonia and nitrites, eventually nitrates. Coupled with the ammonia expelled through the gills, these accumulate in the tiny bowls. That means water parameters will go bad quickly, as ammonia and nitrites are toxic to fish. Without daily water changes (possibly more frequently) these fish will be unhealthy and unhappy.
This does not even touch the subject of space. No living creature was ever designed to be confined in a cage. Not even to mention a cage barely twice the length of the fish. There is no swimming room, which will cause the fish to grow abnormally. There are no decorations to provide cover for the fish, and no proper oxygenation as still water gets depleted from oxygen rapidly.
If you want to keep these fish then get them a proper aquarium that will at least maintain their water quality at acceptable levels, and allow them plenty of hiding spots and freedom to swim around, even if they are not active swimmers.
There is obviously an ongoing debate whether you should be caging any animal, such as aquariums, zoos etc. but I believe there are some merits in doing this for both educational reasons and connecting with nature, especially to animals one would never get to see otherwise. But this has to be done in a sustainable manner, and only animals "fit" for a life in captivity should be chosen. I say "fit" because that is a very loose term. For me it means an animal that would not be adversely affected by a life in captivity. For instance, putting elephants, lions, jaguars, birds of prey etc. in a cage are wrong. They need open space. I can kind of accept a park like the Lion Park in South Africa, it is still small enough that you are guaranteed to see the lions but large enough that they have some freedom. A zoo is not the place for a lion. Same with fish - do not keep Angelfish or Morish Idols etc., fish that have low success rates in captivity and that is almost impossible to breed in captivity. Rather keep captive bred clown fish (without the host anemone), fox faces etc. All fish that adapt well to captivity.