Small Twin Sharks

The Small Twin Sharks were the secondary antagonists of the film Deep Blue Sea.

Biography
They are two completely identical male Mako sharks who were caught and brought to Aquatica along with the third shark, a much larger female to be used as a test subjects as Aquatica's crew tried to create a cure for Alzheimer's and used sharks for it. They were experimented on and fluids from their brain were harvested to create a cure from them, but their brains were too small to provide enough fluid so Susan and Jim mutated them to increase their brain size. This had the side effect of them becoming bigger, smarter and more dangerous, developing the ability to swim backwards, although the third shark took it much farther than her brethren and became a monstrous Big Shark and leader of the trio.

The two sharks didn't reach even half of her size, but were still bigger than normal Makos, reaching roughly 4 meters. One night, one of them escapes from Aquatica presumably by jumping over the fence and attacks a boat full of people, but Carter saves them, captures him again and takes him back to Aquatica. This incident makes Franklin go to Aquatica.

Later, they tear apart a Tiger Shark that is being fed to them, witnessed by Carter. They attack him on the night of the experiment, but retreat when he draws out the gun. After this, they disable the cameras and aren't seen again during the experiment and ensuing chaos with all the spotlight belonging to Big Shark. After the explosion and flooding of Aquatica, they make their way inside. One of them knocks out a door near the crew and tries to attack them, but they manage to escape.

Later, one of them finds and attacks Preach in the flooded hallway. He manages to escape and hides in the kitchen while he swims past him and swims away. However, he later returns and eats his parrot before attacking him again. He gets into the oven and the shark traps him inside, but he escapes and throws a lighter at the shark exploding and killing it.

Later, when Big Shark kills Franklin, the remaining small shark swims up to her, rips off his upper body and swims away with it. He doesn't follow the Big Shark to the shaft and does not partake in Janice's death. When Carter and Scoggs go back to the lab, he swims past them without attacking. She eventually finds her way in Susan's room where she finds and attacks her. Susan narrowly escapes, climbs onto a table and uses the cable to electrocute him, finally killing him.

Trivia

 * They have not killed humans in the film; since all human victims were killed by Big Shark. Their only victims are a tiger shark and Preach's parrot, with one of them snatching Franklin's upper body.