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there are lots of fish feeding on land insects. crickets, flies grashoppers, even snails.
but these fish are all freshwater or at the most brackish water like arowana, archer fish, butterfly fish.
All of these fish are more or less specialized in this kind of prey. so for them it's not harmful. It's likely that an octo never saw a snail up close. maybe he'll eat it. but I would also be on the safe side and not risk it.
maybe you can sell the snails to a french restaurant that serves "escargot" (for those who don't know escargot is french for snail)