The traditional fish bowl is supposed to be filled 2/3 maximum,
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I had a comet goldfish for 9 years in 1/2 gallon bowl and never filled it more than above. No decor no substrate.
The cool thing with Fish bowls and jars, is that you can move the thing at will. And "Peanut" loved to be installed in the sunlight for a while during the day and was happy to be dragged around to follow our activities. And would greet you at each visit you made. I changed his water everyday, 3285 times in his life.
Maybe the jar can be OK for cherry shrimps ? They are good at room temp and have a very light bioload. So a small sponge filter with a weak air pump have good chances to be enough. Since it seems that the less you take care of them the better they go.