The wetlands shrank as they and creeks were diverted for farming, water was exported and dams were built. Non-native fish that prey on the pupfish were also introduced, further shrinking their numbers. By 1948, it was believed the species was extinct. In 1964, a small population of Owens pupfish was rediscovered in Fish Slough. Pupfish feed on insect larvae and aquatic plants.
Some species can survive in warm, salty water that has low levels of oxygen.
Pupfish are extremely territorial, and the males will fight aggressively to protect the area they claim. The Owens tui chub is a species that survives in the quiet, sluggish waters of the slough. Chubs feed primarily on insects and aquatic plants. Spawning occurs from late April through June, in shallow areas with lots of vegetation. Like the Owens pupfish, the species is endangered mainly because of loss of habitat and the introduction of exotic fish species that prey on the chub.