My niger is aggressive. Not terribly but he does snip at other fish. Also kills snails, or else its the small puffter. But the snails are about 5 times the size of the puffer. He is bold to, mine will never swim away, and gets pissed when I put my whole hand into my tank and sometimes attacks it! He is awesome thought, as he has a nice personality. Funniest thing ever is to see him pick up hermits and throw them around.