Flying Seahorses are a variant of regular seahorses, known for their ability to fly when provoked. They are found throughout salt water lakes in Scotland, the most notable being the Black Lake.
A popular sport at Hogwarts School of Witchcraft and Wizardry in the 1990s was a game called "Flying Seahorse Fishing", in which one would use the Seize and Pull Charm on the flying seahorses.
This was more than just recreational, however; they were a necessary ingredient in the Girding Potion, and Professor Severus Snape requested that each member of the class bring in three flying seahorses. Consequently, flying seahorse fishing was essential.