A Shrake is a magically-created species of fish, found in the Atlantic Ocean. The creature is covered in spines and seeks out and destroys Muggle fishing nets. The first Shrakes were supposedly created in the early 1800s by a group of wizard fisherfolk who had been insulted by Muggles. The shrake, by damaging the nets used by Muggles to fish in that area of the sea, cause no end of trouble.
"Shrake" comes from the words "shred" and "hake", a fish related to cod.