Two years or so ago, my wife wanted to buy a freshwater puffer, so we went to petsmart to get dwarf puffers. We bought five tiny little 1/2" puffers thinking that they were juvenile figure eight puffers and took them home. They went into a dedicated 6gal bowfront tank of thier own. In less than three days, four of them were dead and one was left swimming around and gloating. I did some research on juvenile figure eight puffers and they said that a larger group of young puffers would do better, so we went back and bought eight more and put all of them in a 20gal tank of thier own. Again, carnage and death - one little puffer was left alive again. Furious, I wanted to take the last one back, but my wife wanted to keep her little pea-sized killer, so back into the 6gal he went and I tried to forget all about him. I actually hoped that he would eventaully die, but alas, he did not. Flash forward about 1 1/2 years later. I got tired of his dark little dingy tank and put him into a heavily planted 5 gal tank in my bedroom that had been the scene of a shrimp disaster and he floated around quite happily, never bothering the five remaining shrimp nor the two oto cats nor the bumblebee goby (I know he is brackish water). Then one day, I bought a fish magazine, and there was an article on pea puffers! Turns out my little devil was not a young figure eight puffer at all - he was a pea puffer! At this point he was part of the family, my 1yr old daughter even called him "Puff'rrr," and when I reduced my collection down to one small 15gal tank, he remained. Last month, I got tired of just seeing him swimming around, seemingly alone, in a beautiful planted tank, I went out and got a half dozen shrimp, and two weeks later a pair of dwarf guaramis. Much to my surprise, he didn't bother any of the new inhabitants. Granted, the guaramis are three times his size. If just goes to show you, compatability is just way to hard to really frame as "it will live with this, but not this..."