As a type of flattened fish, stingrays and skates share many common characteristics. These cartilaginous fish have no bones and breathe from five to seven gills on their underside. Closely related to sharks, stingrays and skates have tough skin that protects them and streamlines their movements. Scientists believe there are 600 ray species and 500 skate species that exist, but not all rays have barbs that characterizes stingrays.
The main difference between stingrays and skates is their means of reproduction. Stingrays are viviparous, which means they give birth to live young. However, skates lay eggs, making them oviparous. Skates contain their eggs in a thick leathery pouch commonly called a mermaid's purse. The pouch protects the egg until the skate pups emerge.
Stingrays acquired their name for the sharp barbs on their tails, which inject poison into the victim. The barbs rise from the tail at an angle to maximize damage and keep the victim from escaping. Skates lack these barbs and use their stronger tails with short but sharp projections to protect themselves. These thorns cover the back of the tail and extend across their backs and fins.
The stingray bears whip-like tails that tend to be longer than their bodies, while skates have shorter and fleshier tails. Skates also have a dorsal fin running down their spines and onto their tails. Stingrays have a smaller dorsal fin or none at all. Skates generally don't grow as large as stingrays. Although skates grow up to 8 feet across, the largest rays - the manta rays - reach nearly 30 feet from fin tip to fin tip. Stingrays tend to be kite-shaped, while skates have rounder bodies.
The size difference between stingrays and skates parallels their different diets. Stingrays bear large, plate-like teeth to crush larger fish and prey. The skates must eat smaller foods than stingrays, so they only have small teeth. Some stingray species can live in brackish water and freshwater, but skates have a stronger tendency to remain in marine waters. Stingrays pose a larger threat to human beings than skates, but both animals rarely attack people.