Fish (Phylum Chordata, Subphylum Vertebrata) are found in all types of aquatic environments, from fresh to salt water. Common methods of introduction include intentional and accidental stocking, release of bait fish, release of unwanted aquarium fish, escape from aquaculture facilities, and discharge of ballast water. Potential impacts include competition with native species for food and habitat, reduction of natives by predation, transmission of diseases or parasites, and habitat alteration. One example is the inland silversides, Menidia beryllina, which was illegally introduced into Clear Lake, California, as a nutrient reservoir for bluegreen algae blooms and to reduce the Clear Lake gnat and chironomid midge populations. As a result of this introduction, the silversides have competitively displaced several native fish species, including the now extinct Clear Lake splittail.