Koisioth (リュガノス, Ryuganosu) is a Piscine Wyvern.
Koisioth is a large Piscine Wyvern that is covered in shiny, purple, fish-like scales. Its head is fish-like in nature, with rounded features and a sharp, narrow snout. Their mouth is filled with sharp teeth and their eyes are a pale green. It has a pair of large pectoral fins. Its legs are stocky and wide-set and end in clawed, webbed feet. It has a long, thick, paddle-like tail. The webbing on their pectoral fins are a crimson color while their feet and tail have gray webbing.
Unlike most Piscine Wyverns, Koisioth is capable of flying with skil comparable to that of Flying Wyverns like Rathalos and Seregios. It is also an excellent swimmer, using its fins and tail to propel itself through the water at high speeds. Koisioth is able to use the Dragon element, something that also sets it apart from other Piscine Wyverns. It uses the element when enraged, drastically increasing the power of its attack.
Koisioth are said to be mild-mannered. Like most large monsters, it is territorial and will attack intruders on sight.
Koisioth are commonly found in large bodies of water in a wide variety of environments, such as the Jungle, Flooded Forest, Primal Forest and the fresh waters surrounding the Misty Peaks.
- Koisioth is based on a legend about how carp that leapt over the Dragon Gate would become dragons. This explains Koisioth's ability to use the Dragon element. It is also based on the Asian carp, which are easily frightened by disturbances in water and can jump 8–10 feet (2.5–3 m) in the air.
- When in the air, it can knocked down with a Flash Bomb. In the water it can be forced out with a Sonic Bomb or a Frog.
- Its fins, feet, head, and tail can be broken.
- When fatigued, Koisioth won't be able to use its dragon element attacks.