I do not recommend putting a lionfish with a sargassum. Anything that can fit in either of their mouths will be eaten. i have kept some sargassums for a while and they are very cool, but hard to get to eat. We started them out with live Cyclops or ghost shrimp. Eventually we got them to eat frozen large krill, but we had to put the food on a stick and make it look very life-like. It took a while but eventually it was fun to feed them. I would definately make sure that whatever you put the sargassum with it is much bigger than he is. We were quarantining them and treating them and someone made the mistake of putting 3 gobies in with them while performing the treatment. Needless to say all the gobies were gone within five minutes.