This is great. I love all the little details (the way the inflated blowfish pops when hit with a dart, for example), and the levels are designed to teach you how to use the mechanics in a very thoughtful way. I really enjoyed this.
Also (shameless plug), it's funny because I made a game about a balloon that has to catch gusts of air to stay afloat, and I originally considered making it a blowfish that could inflate or deflate. Give it a look if you have the chance. ;)