From Piranha to Pacu: Top 5 Scariest, Weirdest Fish that Would Give You Nightmares

Animals can be cute, but sometimes, evolution plays around and spawns terrifying creatures that are what nightmares are made of. From the world-renowned piranha to the Pacu fish with human-like teeth, here are the top five scariest looking fish from the weird underwater world.

1. Red-Bellied Piranha

We start off the list with the most famous of them all, the piranha. This species, according to Extreme Science, thrives in the Amazon and has a reputation of being aggressive as it does not choose who or what it eats -- may it be a small fish, a human arm or a giant cow.

Piranhas are known for their extremely sharp teeth, which are powerful enough to rip apart flesh or toe from unwary victims. Their teeth are so sharp that they are used in weapon-making.

2. Pacu Fish

Last week, a mysterious fish with human-like teeth was caught in New Jersey, and it turned out to be the South American fish called Pacu.

The tropical species has been rumored to eat male genitalia. However, National Geographic debunks this myth as the Pacu fish, though scary looking, are omnivorous animals that mostly feed on plants.

3. Vampire Fish

This fish could be the Dracula of the underwater world. Vampire fish or payara (Hydrolycus scomberoides), according to the National Geographic, have long sharp fangs that could grow up to six inches long and impale even the fierce piranhas.

4. Cyclops Shark

A cyclops shark!! https://t.co/szD1C12l #sharkweek

— NPR (@NPR) August 13, 2012

The Cyclops shark's appearance is in between cute and weird. Not a species per se, this rare sea creature is a result of a nature anomaly. Sporting one giant eye, it looks like Mike Wazowski from the animated film "Monsters, Inc."

According to Live Science, the Cyclops shark has a development anomaly called cyclopia, which results to animals (or even human fetuses) developing with only one eye. In 2011, a Cyclops shark was discovered by a fisherman after cutting open a pregnant shark. Cyclops shark don't survive long in the wild and none have been caught outside the womb.

5. Frilled Shark

The frilled shark (Chlamydoselachus anguineus) may be the record holder for having the most terrifying mouth in this list. This bizarre species was discovered in the 19th century and was popularly called "sea serpent" at that time.

Mental Floss notes that the frilled sharks look like giant snakes with a lizard-like head, long body, and huge mouth. Perhaps, one of its weirdest characteristics is its insane set of teeth. The frilled shark's huge mouth is lined with 25 rows of backward-facing sharp teeth (300 in all).

Frilled sharks can be found in most parts of the world but are hard to spot as they rarely go to the surface of oceans, living in depths between 390 and 4,200 feet.