Why are there aquariums with eels in front of most Donkis in Japan?

I wonder if there is a historic reason. Not that the shop being named after Don Quixote made much sense in the first place…

Also, is it normal that nobody around me, animal lovers included, seems shocked or even questions that such animals are stuck in tiny aquariums like that?

I feel so sorry for them every time I walk past a Donki (and sorry for the eels too).