Let me break it down for you.
If you get stung by a lion (dwarf) or volitain it will hurt a lot. I know I got tagged by a small volitain while I was working at a lfs once. Definitely not an experience id like to repeat. It literally feels like your hand is on fire...
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Yup, I got tagged with three spines from my red volitan long ago, and he was almost 6".
Burned like mother for about 24 hours and was swollen for few days.
BUT if you are sensitive it can be lethal. We had a customer that got stung in the finger be a black volitan about 4". He had a bad reaction to it, his entire arm up to the shoulder almost doubled in size and he was hospitalized for two days.
Needless to say the next time we saw him his arm was bandaged and swollen and he had the lionfish in a bucket returning it.
also saw my boss at that store get his fingertip shredded by a baby snowflake, it bled for hours.
Having said all that, triggers, some groupers, large tangs, similarly sized and temperament fish would be ok with lions and eels, but they really need at least a 125 to make it work.
One other thing to bear in mind is that as the fish grow and their relative sizes to one another change, so does the aggression and territorial dynamics in the tank.
Basically, a fish that is a good citizen at 3" may be a holy terror at 5" if it thinks it is now big enough to take on the other inhabitants. I have that issue now with a blue fin damsel. It was fine when I first got it, but he has almost doubled in size and is now the second largest in the tank and he is relentlessly tormenting everyone else now.
He
won't be making the move to the bigger tank this week. LOL