Widemouth Blindcat (Satan eurystomus) , is 1 of 2 cave-dwelling catfish in the Edwards Aquifer. These two troglobotic catfish display some of the most extreme cave morphologies of any known cave fish. [Photo: Texas State University at San Marcos]

The Edwards Aquifer is one of the most diverse subterranean habitats in the world. It has approximately 45 troglobotic (obligate cave-dwelling) species and many other species that can live in both surface and subsurface environments (troglophiles). Due to the island-type isolation of gene pools in these habitats, cave-adapted speciation can occur; and depending on the time scale of isolation, these cave morphologies can be extreme. Scientists have hypothesized as to what types of pressure influence these adaptations, and two hypotheses have emerged as likely. The first is energy economy (i.e. adaptation to limited food supply); these adaptations manifest as low metabolic rate, small size, lack of body pigment, and lack of eyes and wings (in insects). The second type of adaptation is a hyper development of characteristics used to locate food and mates. These traits become hyper-sensitive in response to cave environmental conditions (i.e. no light). These adaptations appear as enlarged sensory organs, such as large nostrils, over-developed lateral lines, and enlarged barbels.