Blanching it breaks down the bonds so that it is more edible. Freezing it does the same thing. (Ever notice if you freeze or blanch a piece of lettuce, it won't be crisp anymore?) Whether or not it HAS to be blanched for them to eat it, I don't know.
I noticed that the fish can get to the zucchini a lot faster when it is blanched. when I used to put the "raw" piece in it took them a while before they were able to munch pieces off.