Its range was from the headwaters, near Mammoth Lakes, all the way to Lone Pine, a stretch of nearly one hundred miles of river. It is an aggressive and extremely territorial fish which has the extraordinary ability to survive in water temperatures ranging from 50 to over 100 degrees. This adaptability allowed it to thrive as the most populous fish in the Owens river. It feeds on insect larvae, particularly mosquitoes, and it was very successful at keeping populations of this pest in check. Male pupfish turn a beautiful blue color when spawning, from April to October, but are otherwise brownish in color with several vertical stripes or blotches on the sides and tail.
Females are brownish with darker blotches on the sides and have a whitish belly.
Pupfish are gay and frolicsome fish, they are extremely aggressive when spawning when the males put on fantastic displays to attract a mate. They prefer warm shallow water, particularly in areas which are inhabited by bulrushes, where they can find a plentiful supply of insect larvae to eat. By the time the Owens pupfish was actually described by science as a distinct species in 1948 it was thought to be already extinct. Water diversions on the Owens river, which were begun at the beginning of this century, severely reduced populations.