Like said, they are not a brackish fish. The only time salt is needed to is induce spawning moods.
Out of the family Belonidae, they are the only one that I know of that are truly freshwater. All species have been known to interchange waterways; going back and forth from brackish, freshwater, and saltwater. But Xenentodon cancila is the only one that stays in freshwater. Many people seem to confuse them with their silvery, saltwater cousins. Honestly, I really can't see why though. Cancila grow to about a fourth or third of the size compared to the others, rarely found in pure saltwater, primary color is a tannish body with a black lateral line compared to the primary silver color that dominates others, etc.
In the wild, they feed mainly on fish, insects, and small crustaceans like mentioned. Bugs that fall on the surface are a big part of a daily diet, with fish being maybe the second. In an aquarium setting, fish dominate over everything, as they're much easier to catch then in a large waterway. Please though, get them off of feeder fish. It's not that hard despite all the rumors going around, just don't be afraid to starve your fish for a week to two weeks. Depending on the individual fish, it could start eating in a few days. Just about everyone i've had has been switched over (have had like seven or something close) so that really says something. Let me tell you, they do so much better on freeze dried krill and market shrimp, you'll see the difference right away. While it should be a staple diet, you can offer a feeder fish or two now and then. If you just got them, plump them up with a few fish for a couple of days before you start weaning onto other foods. They're stressed enough as it is, and if they haven't eaten before you starve them, it could cause problems. If they've eater before and are starved for about two weeks (the longest you'll have to wait), then nothing bad should really happen.
As for tank size, length and width are important, al in all though..length is THE most important. Width should be about 12 inches for most individuals, but of course, the larger the better. In the end you'll need a 50-60 gallon. My almost fully grown needlenose is in a 65 and loving it.
Beefheart...only as a once weekly snack. Helps in growth but if it's a major diet item it will become deformed someway in the long run. Had to throw that in at the last minute...
I hope people will stop messing up info on these fish saying they're brackish,etc. These are one of my favorite fish, but sadly no one really knows much about them. I'm trying to get an article in Aquarium Fish Magazine..but I haven't gotten a response yet...sucks really. I've kept countless ones and currently did a little dissection thing on a small one that died a while ago, and I have a three year old or more dominate male needlenose. I guess you could call me a needlenose freak lol. Ever need anymore help feel free to post it!
/fish.mongabay.com/species/Xenentodon_cancila.html
CFC
