and their allies) that causes whirling disease in pen farmed salmon and trout and also in wild fish populations. It was first described in rainbow trout introduced to Germany a century ago, but its range has spread and it has appeared in most of Europe, northern Asia, the U.S., South Africa and other countries. In the 1980s, was found to require Tubifex tubifex (a kind of segmented worm) to complete its life cycle. The parasite infects its hosts with its cells after piercing them with polar filaments ejected from nematocyst-like capsules. This parasite was originally a mild pathogen of brown trout in central Europe and other salmonids in northeast Asia, and the spread of the rainbow trout has greatly increased its impact. Having no innate immunity to , rainbow trout are particularly susceptible, and can release so many spores that even more resistant species in the same area, such as , can become overloaded with parasites and incur mortalities of 80 to 90 percent. Where has become well-established, it has caused a decline or even elimination of whole cohorts of fish. The parasite was first recorded in North America in 1956 in Pennsylvania, but until the 1990s, whirling disease was considered a manageable problem affecting only rainbow trout in hatcheries. It eventually became established in the natural waters of the Rocky Mountain states (Colorado, Wyoming, Utah, Montana, Idaho, New Mexico), where it is damaging several sport fishing rivers. Some streams in the western U.S. lost 90 percent of their trout. Whirling disease threatens recreational fishing, which is important for the tourism industry, a key component of the economies of some U.S. western states. For example, in 2005 anglers in Montana spent approximately $196,000,000 in activities directly related to trout fishing in the state. Some of the salmonids that infects (bull trout, cutthroat trout, and anadromous forms of rainbow trout—steelhead) are already threatened or endangered, and the parasite could worsen their population decline. New Zealand mud snail The New Zealand mud snail , once endemic to New Zealand, has spread widely and has become naturalised and an invasive species in many areas including Australia, Asia (Japan, in the Garmat Ali River in Iraq since 2008), Europe (since 1859 in England), and North America (U.S. and Canada: Thunder Bay in Ontario since 2001, British Columbia since July 2007), most likely inadvertently during human activity. It can reach concentrations greater than , endangering