Thank you Marcha, for providing a distinction between cold water and tropical fish, and their individual needs. Although, I would never have put dogs (especially senior aged dogs) and fish in the same sentence when pointing out care and maintenance matters....
I am familiar with "Japanese Fighting Fish." I have been told that if males are in the same space, they will "fight." But I do recall their colorful markings, and a murky water environment.
I am leaning more towards the lower maintenance type of fish. I will check out the links you provided, and take it from there.