LOL!!! Well, there's those fish again. LOL
I also believe these small containers - with SCREW caps - were made to carry something other than priming powder. It would simply be inconvienant and take too long unscewing a cap versus simply pulling out a plug or pushing on a lever to get access to the powder.
While screw style plugs are not unknown, they only seem to appear on European styled powder horns - for sporting purposes. And even then, they are seldom encountered unless made sometime during the 20th Century.
So I think the originally posted flask above falls into the same catagory as the fish shaped flasks posted by Kubur and Corrado. And if brass, probably of Indian origin.
As a comparison, here is a fish shaped, painted wood flask that does look old. I picked this up from Oriental Arms. Artzi says it's likely of South Indian origin. I ran a long Q-Tip through the flask mouth, and rubbing around produced a small evidence of black powder. So I think this one was used for priming a matchlock of some type. Notice the mouth of the flask was made for a plug, now missing.
Still, I like the design of the flask originally posted. Would clean up very nice.
Rick