from the "great fish" that swallowed Jonah the Prophet through to the half-human, half-fish mermaid around which books and movies have been centred (e.g., Splash). Among the deities said to take the form of a fish are Ika-Roa of the Polynesians, Dagon of various ancient Semitic peoples, and Matsya of the Dravidas of India. The astrological symbol Pisces is based on a constellation of the same name, but there is also a second fish constellation in the night sky, Piscis Austrinus. Fish have been used figuratively in many different ways, for example the ichthys used by early Christians to identify themselves through to the fish as a symbol of fertility among Bengalis.[38] Fish have also featured prominently in art and literature, as in movies such as Finding Nemo and books such as The Old Man and the Sea. Large fish, particularly sharks, have frequently been the subject of horror movies and thrillers, most notably the novel Jaws, which spawned a series of films of the same name that in turn inspired similar films or parodies such as Shark Tale, Snakehead Terror, and Piranha.
Introduction of exotic species has occurred in a 
variety
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variety of places and for many different reasons. One of the nest studied (and most severe) examples was the introduction of Nile perch into Lake Victoria. Since the 1960s the Nile perch gradually exterminated the 500 species of cichlid fishes found only in this lake and nowhere else. Some species survive now only in captive breeding programmes, but others are probably extinct.[37] Carp, tilapia, European perch, brown trout, rainbow trout, and sea lampreys are other examples of fish that have caused problems by being introduced into alien environments.
