I've had my Fire Eel, Squishy for around 2 and a half years now, I got him when he was only 3.5" big, he's actually the reason I started keeping larger fish, I had a betta in a 5 gallon, and saw Squishy at the store, I asked the guy if it would be fine in a 5 gallon, I was told yes. Boy, was I in for a surprise when I got home and found out they can grow up to 40".
1. Squishy grew pretty fast, once I had a proper tank, I grew him with an oscar and a delhezi bichir (the bichir was already 6" or so when I got it), but the oscar was just over an inch and they grew roughly at the same rate (the oscar was a bit faster) for a little while. I would say almost an inch per month for the first 4 months (he would have been about 7 or 8" by then), then for then about 4 months later he hit 10 or 11" After that he slowed down quite a bit after those first 8 or 9 months. Now around 2.5 years old he's almost 20" Which isn't bad, about 3 months ago I bought another one, which I'm growing out with a clown knife fish, a couple bichirs and a lima shovelnose. The new guy seems to be growing a bit slower, feeding it twice a day, a diet of chopped fish, shrimp, mussels, clams, oysters, prawns, and bloodworms.
2. Squishy started hand feeding soon after I brought him home, but he would often stay hidden, burrowed in the sand or behind some plants most of the day. It wasn't until he hit about 7" he actually came out more often and would usually interact with my hands while I was doing water changes and and some times he would bite me. Once he got around 12" he would come up to the tank whenever he saw me, he seemed very enthusiastic when I was near. His head would bob up and down, while he stayed afloat by moving his body in an "S" shape. Now he still does the same thing, it never fails to make me smile. He has almost always been the first one there for feeding time, so he gets first pick of all the food, during my lazy days when I just dump the container in the tank (rather than giving a bit at a time) as I start to put it in the water, he pulls it down and pushes his way in so he can get his favorites before the other fish can. As soon as the tank lid opens he sticks his head out of the water with anticipation of food. I would say out of all the fish I've ever had my fire eel is the most interactive and playful. He does allow me to pet him, I try not to though since their skin can be sensitive. When I do have my hands in the tank he'll often rub up against them. I hate to pick favorites, but I would say he's definitely at the top of the list. Keep in mind though, if you continue hand feeding when it gets larger, they do miss the food every so often and the bites can be a bit rough, he has broken my skin more than a few times. The new guy is not very interactive yet, but I hope that changes soon.
3. Squishy is the biggest in his tank right now, he's lived with rope fish for a bit over a year now, I recently got a couple more about two months ago, they're about 6" long, he hasn't tried to eat them. When he was about 11" I added in a 4 or 5" ornate bichir, and there were never any problems. I also had him with a vampire knife fish that was fairly small, and he was probably 14-16" and again, I still have it, he didn't try to eat it. I've never come home only to find him chomping down a tank mate. I do give him feeders though, usually platies mainly, but the biggest I've given him would be 1.5" goldfish feeders. I think as long as they're wider than their mouth or 1/3 of their length there shouldn't be a problem. Although, I did have a friend that came home to find his 10" fire eel eating his 5" pictus catfish. I think it depends a lot on how much space there is in the tank as well, like I said, when I first got him, he was in a 5 gallon, a few days later I had him in a 30 gallon, once he hit 6 or 7" he was in a 180 gallon, where he is now as well. He'll be moving into a bigger home soon. As well as tank space I think it does also depend on how well fed they are, and the personality of the eel itself, some tend to be more aggressive than others, mine just happens to be very passive, he's been with aggressive tank mates before, but they always left Squishy alone, even the extremely territorial ones would always let him hang out in their section of the tank. I don't think he's ever gotten one scratch from another fish on purpose.
