Hmm...sounds strange. Do you have any other stuff for it to eat beside zucchini?
When they get to be about 1", they eat frozen blood worms. They also LOVE driftwood (real driftwood) not fake plastic stuff. Algae on the tank would also be good if you have any. How about plants? They also help clean the leaves of plants and eat some half rotten plant matter (at least mine does).
They are really hardy and not all that demanding. Could it be other fishes are attacking them while you are not looking?