I know that the eel has to be in brackish water im just waiting till my brother gets his tank setup then im probably going to put the puffer fish in that tank too, though the puffer fish didn't match any of the photos on your link, im not even sure its a puffer ( a random women gave it to me and said it was a puffer but didn't know what kind), it looks like one but it hasn't matched any of the pictures. As for the pacu, I intend to keep it, its a baby right now and i know how big they get hence why im waiting to get a bigger tank. Greater sirens don't need land they live just fine being fully aquatic, that being said i do have land in my tank, i guess i never said this but my tank is a paludarium, i siliconed two pieces of glass together to form a box full of gravel on the bottom, a screen over the gravel and soil on top with plants growing. I realize that my stocking of fish is very bad, i didnt plan on having these fish, its just people didnt want them so i took them except the peacock bass that i actually bought. The feeder fish are actually for my tegu, I give her about 2 a week just to keep her hunger satisfied till i get mice the next week. So what fish should i put the greater siren with? and I thank you for warning me.