|Pupfishes are closely related to the killifishes. The name pupfishes came from the mating habits of the males which resemble frolicking puppies at play. Many of these small fishes are found in extreme and isolated habitats, from scorching hot desert marshes to deep-water caves to waters three times saltier than sea water. Some are popular aquarium fishes while many others are considered endangered, threatened or a species of concern. One species, the sheepshead minnow, is common in Texas' brackish waters.