Gyrodactylus leptorhynchi is a small monogenean (about 0.5 mm long) obligate ectoparasite which parasitizes freshwater Bay Pipefish. Gyrodactylus leptorhynchi is the seventh Gyrodactylus species known to infect Bay Pipefish and the first characterized along the Pacific coast of North America. The parasite can get into captive fish environments, such as fish farms and aquariums, where it may spread in as little as 10 days. Gyrodactylus species are known to centralize on the brood pouch in male fish, this may allow. for transmission to newly hatched young. However, in Gyrodactylus leptorhynchi the parasite was found mostly found attached to body surfaces such as the dorsal fins.