Whether you are cremated or not, the fish are still going to have a go at you. Perhaps fifferent fish: a shark would prefer to snack on your corpse, but as ashes, you might be more toothsome to a plankton.
Romans used cremation. More hygienic and does not take good farmland out of circulation. The Zoroastrians favored disposal by buzzard, which does not go well with increased urbanization. Nothing puts a guy off more than when a buzzard drops a corpse finger in his Fetuccini Alfredo.
The original reason for Christians to favor burial was (a) it was what Jews did, a habit they got from the Egyptians. Appropriate for Egypt, a country where most of the country is perfectly suited for burial: there is no other good use for the desert, and it helps mummify you. Then Jesus went and rose from the dead, and it became dogma that everyone was gonna get their body back, as in "I believe in the resurrection of the body" in the Apostles Creed.
God, of course, is omnipotent, capable and willing to resurrect a blessed martyr from an assembledge of lion turds, but the idea of the Holy Mother Church is that cremation is just making God's job too unnecessarily difficult.
Finally, unless you are buried, you have no hope of ever becoming a zombie.
