User blog comment:Twentypence/Dragon Pages info/@comment-25095131-20140627034144/@comment-9871338-20140627133704

If you decide you don't want a dragon any more you can release them, freeing up hangar space. In exchange for this you get fish equal to a certain number + 1/4 of the fish spent upgrading the dragon so far (including that spent on partial level upgrades). I think this might be something to go on a game mechanics page at some point.