BARRACUDA (1978)

So the same year that Jaws 2 came out, we also got Piranha and this.  Wayne Crawford (who had already been in God's Bloody Acre (1975), by the same director, Harry Kerwin) plays a marine biology student who is testing the ocean out near a chemical plant.  The plant's owner, played by character actor Bert Freed, has him arrested by the sheriff (played by William Kerwin, Harry's brother and star of the H. G. Lewis classics Blood Feast (1963) and Two Thousand Maniacs (1964)).  People out swimming or fishing are getting attacked and killed by barracuda.  Crawford gets out of jail and does some more testing (at one point he has a couple barracuda heads on a desk!)  Eventually he finds out that the chemicals are making the fish hypoglycemic and that is what makes them attack!  There is even something more sinister afoot, as he soon finds out.  The attacks are not gory and even when someone finds a head on the beach you really don't see anything.  It's still pretty fun to watch and keeps you guessing.  This was Harry Kerwin's last movie (he died in 1979).