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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.
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