“If you have an aquarium with fish in it and want to add more, you have to determine if the new fish are compatible with the existing fish. Some fish are more civilized than other fish.”
True. Some fish will kill the others.
I had a 55 gallon aquarium and looking to add some fish. Told the fish store that I had several large angelfish that I had for several years and the African cichlids would leave them alone. Took them all back in the next day after the cichlids decimated the angelfish’s fins. Cost them a pretty penny.