Hello Mike, welcome to the forum!
Well, there's a couple things worth mentioning here. First "red-eye puffers" can mean a variety of things. Strictly speaking, the name belongs to
Carinotetraodon lorteti. This species is a bit aggressive and nippy, and is normally kept in a single species aquarium. A second species,
Carinotetraodon irrubesco, is sometimes called the red-eye puffer though it is more precisely the red-tailed red-eye puffer. It isn't so aggressive and can be kept (thought not 100% reliably) with fast-moving tankmates such as tetras. Some specimens even of this species turn out to be fin-nippers.
I suppose it is also possible that some of the
Tetraodon species might be sold as red-eye puffers, as some of them have red eyes, but I've not seen this in practise.
So do you know which species you have?
From my experience of
Carinotetraodon irrubesco and South American puffers, I'd consider silver sharks and plecs safe, mollies at risk, and gouramis likely to be at risk. Certain fish are either too slow or too stupid to avoid pufferfish. Others are too fast. Plecs simply return any attacks ten-fold and have the bulk to reinforce their point, so most fish learn to avoid disturbing them!
Anyway, none of these needs brackish (salty) water. In fact, they prefer soft to moderately hard, slightly acidic to neutral, freshwater.
Cheers,
Neale
I have 4 very small red eyed puffer fish which i have mixed with gouramies, plecs, mollie and a couple of silver sharks. I have been told that red eye puffers are usually not too aggressive towards other fish. Is this the case and will they be safe with the fish I have listed in 188litre tank? Also, I understand that these fish can require small amounts of salt as they mature. How much would they require and what sort of salt do I need to buy?
Thanks
Mike