The reason I got into brackish water fish (and ended up writing a book about them) was precisely because fish shops often don't know what they're selling. Around about 1991, I bought a couple of "freshwater puffers" I'd never seen before. Eventually, I found out they were juvenile
Arothron hispidus, a marine species that happens to breed in estuaries and has a high tolerance for freshwater. Over the years, I've collected information about many brackish water fish species sometimes sold either as freshwater fish or marine fish. I try my best to get this information out to hobbyists, either through my book, or my web site, or in magazine articles.
Here's the thing. It's all very well getting annoyed with me for telling you something you don't want to hear. I can understand that; it's a very human reaction to bad news. But the reality is that you don't need to re-discover the preferences of a species like
Tetraodon erythrotaenia. They're out there, in the scientific and advanced hobbyist literature. There's no conflict at all in the literature: these are brackish water fish. The fact your pet shop didn't know anything about them is unfortunate but not an excuse; nobody would be foolish enough to buy a mysterious fish before reading up on them... or would they?
Tetraodon erythrotaenia may well do fine in freshwater for long periods, particularly if the water is clean, hard, and has a basic pH. But if the figure-8 puffer is anything to go by, it will live much longer, and be much more disease resistant, in brackish water. Since the species hasn't been traded much until the last year or so, we really don't know exactly how big a difference proper maintenance would make. In the case of the figure-8 puffer though, specimens kept in brackish water can live for twice as long!
You can choose not to ask questions. You can choose to be ignorant about what your fish need, and then not worry if they get sick, aggressive, or causes some other problem. If they die, well, that's not the end of the world is it. It's just a fish!
That may well be your approach, but it isn't mine. I'm simply trying to help you keep your fish better.
Cheers, Neale
I wish i hadnt asked. I AM KEEPING THEM IN THE CONDITIONS THAT THE SHOP TOLD ME TO. They have sold lots of these fish on regular basis. I only asked because i have read conflicting imformation. I wont bother trying to comfirm things again. How long have you had yours though?