Dr. Luther Paradigm (Dr. Piranoid or Paranoid): Dr. Paradigm is a university professor, and the main villain. He has a metal eyepatch and later he wears a robotic suit. The suit is heavily armoured and also has offensive capabilities like the ability to fire out harpoons. Due to an accident, Paradigm got injected with pirahna DNA, and turns into the freakish Dr. Piranoid when ticked off. He is responsible for the Street Sharks, his Seavites & many other mutations, not to mention the disappearance of Dr. Bolton and Sara's power to talk to sea creatures. He'll stop at nothing to take over Fission City, make the Sharks & all the citizens his minions, and get back what he believes belong to him; Swimmy, Leaper & Sara's power.

Slobster: Slobster, along with Slash, is one of Paradigm's earlier experiments. He was created by injecting a lobster with the DNA of villainous figures like Ghengis Khan and Captain Blood. He has huge claws that can chop through just about anything.

Slash: Slash is another of Paradigm's first experiments with gene manipulation. A swordfish that was also injected with the DNA of villains like Ghengis Khan and Captain Blood. He has a drill for a nose that can drill through even the thickest metal.

Killamari: Killamari is the third of Dr. Paradigm's Seaviants, created from a squid captured off the Great Barrier Reef in Australia. Killamari has the ability to project natural 'spears' or 'harpoons' from his mouth and the many suckers covering his body- these projectiles drip with an extremely potent venom. He is as nasty as the other guys, yet he & Slash have a tendancy of not getting along.

Repteel: Repteel is the only one of Paradigm's Seaviants to have originally been human. The aged owner of a run-down hotel accidentally demolished by the Street Sharks during a fight with Paradigm's Seaviants, he willingly allowed Paradigm to merge his genetic codes with those of a moray eel and an electric eel.