Also, in my limited experience...
I've found that sometimes it takes a few attempts of offering the zucchini before they will actually try it. If I remember correctly, it took Count (my Sailfin) about 3 or 4 times before he finally gave in and tasted it. Some fish seem to be really nervous about it and will only get so close to it at first.
75G- (3) Firemouth Cichlids, (10) Tiger Barbs, (3) Dojo Loaches, (3) Yoyo Loaches, and (1) Sailfin Pleco.
46G- (3) Pearl Gouramis, (5) Black Skirt Tetras, (7) Harlequin Rasboras, (3) Dojo Loaches, (1) Clown Pleco