Piranha 2 The Spawning (1981)

In a Caribbean island, a couple is found dead inside a sunken ship. The scuba diving instructor of the local resort Anne Kimbrough breaks in the morgue with her acquaintance Tyler Sherman and finds that the bodies have been eaten in many parts. They have one night stand and Tyler tells her that he is a biochemist that have developed a specimen of genetically modified piranha capable of flying to be the ultimate weapon. Unfortunately they had lost a cylinder full of the new breed in the water. During the fishing party promoted by the resort, the piranhas attack the guests. Anne and Tyler decide to explode the ship to destroy the nest of the predator.