Frankenfish

This is a 2004 Syfy film.

Plot
Medical examiner Sam Rivers and bioligest Mary Callahan travel into the bayou to investigate the mysterious death of a fisherman. Having grown up in the area, Sam is comfortable in his surroundings while Mary is not. They find Elmer noodling for catfish in the swamp canals. With Elmer, Sam and Mary travel up river to the fishing community. They meet Gloria, the wife of the deceased fisherman. Gloria's daughter Eliza and her semi-boyfriend Dan also live in the house. Gloria explains that a boat washed up river a few months ago and strange things have happened since.

Sam and Mary find the boat along the bank of a canal. They explore the interior while Elmer waits in the canoe outside. They discover the remains of the crew in the hold. Upset, Mary clumsily knocks Elmer from the canoe and something drags him down. Sam and Mary flee in the canoe, unaware that they have triggered a homing signal on the ship. On the mainland a team relays the information to their employer a wealthy bounty hunter.

One of the villagers heard noises while on his porch. He leans over the edge and a frankenfish leaps up and decapitates him. His girlfriend attempts to escape the houseboat on a canoe but the fish flips her out and kills her. Frightened, the group tries to flee in boats but the fish destroys them. On a neighboring stilt house, Ricardo baits a large hook using an entire catfish and manages to land one of the frankenfish. Nearly as big as a full-grown man, the fish can breathe air and hops forward biting at Ricardo's legs. Ricardo manages to kill it with a shotgun blast to the head. In vengeance he tears out its heart and barbecues it. As he takes his first bite a second frankenfish leaps from the water and devours him.

While everyone panics, Mary declares she has an idea on how to get off the boathouse. Before she can explain a shotgun, left in the still-burning fire from the barbecue, shoots her. The same fire propels a propane tank into the boathouse causing an explosion that sends Eliza into the water. Sam dives in and rescues her at the same time a frankenfish leaps from the water and bites off Gloria's legs. The fish have begun attacking the boathouses, punching holes in them to make them sink.

The bounty hunter and his crew arrive and the fish attack them too. Knocked out of the boat, they swim quickly to the safety of the sinking stilt houses. The hunter explains that the fish are genetically engineered snakeheads. Sam, Eliza and Dan have no choice but to join the hunter in pursuing the fish.

The crew follows a trail of blood back to the fish's den. The hunter forces Sam at gunpoint to enter first. Sam flees the den as behind him a frankenfish kills two hunters. Dan, Sam and Eliza quickly leave on the fan boat, chased by the frankenfish. Dan falls from the boat during the chase but scrambles up a mudbank. Realizing they cannot outrace the monster, Sam drives the fanboat up a stand of tree stumps and knocks off the protective lining of the fan. Unable to slow its momentum, the frankenfish launches into the whirling blades to its death. Sam and Eliza kiss and go back the way they came to get Dan. However, Dan is trapped in the mud as dozens of baby frankenfish attack him.