There are boviously "personality" or "taste preferences" between members of the same species... I should also note my observations on the method of introduction. I inserted 50 of these sand burrowing "illynaeous" snails, (named somethng else on ebay right now where u can buy 200 for ~$20) my peacock showed no interest in killing, defending or eating the massive invasion... Recently, in my brackish (1.0210) my GS Puffer lives in, occasionally doubles as a feeder tank for ghost shrimp, fiddler crabs, and crayfish. I added over 50 ghost shrimp last week for storage, and in the past the puffer would swim around and kill (not eat yet...) as many ghost shrimps as he could till he tired... but not all, and I should note that I would put about 20 or so in at a time in the past. By morning they would all be gone. This time i put in over 50, and he hasnt killed, or even tempted to kill one... and they have been living in there for almost a week now... It almost seems like the puffer is overwhelmed, or something with the feeders b/c he was sulking around for a day or so.... anyways,... it seems that in my experience thus far, when a large population of a species is added, it reduces the desire of a lone predator to attack... or at least in some scenarios....