Every culture has a tradition concerning creation and the great flood, including China.
http://www.pitt.edu/~dash/chinaflood.html
http://www.mythome.org/fludmyt7.html
Speciation is the obvious answer to your concerns about the number of animals on the Ark. Paleontologists are at odds concerning the rate that one species can "evolve" into another, however, all dogs are related to wolves. Tropical fish can tolerate some salt content in water and since we do not know the salt content of the flood ocean it is difficult to answer your question.