depending on how small you get it maybe for a couple of months. I don't see anything wrong with growing up a fahaka for a little while in a 29 but at around 5-6" it will need to be moved to something larger. also, in a smaller tank you'll want to keep a really close eye on the nitrate level because puffers are very messy fish.
fahakas, by the way, are a freshwater puffer species. I only mention because you posted this in the brackish/salt forum.
yeah i grew mine up in a 33g till it was about 5" and that only took a couple months. and they are quite active so they definitely take up a lot of space. like everyone says sounds good as long as your going to upgrade in a couple months.