Cave environments

Caves and other associated subterranean habitats represent some of the most challenging environments on Earth. Despite many significant abiotic and biotic obstacles to overcome, most notably the complete absence of light, several groups of fishes thrive in subterranean habitats. The aim of this chapter is to provide a broad yet thorough review of our current knowledge regarding fish adaptations to one of the most extreme habitats on the planet. We begin our chapter by providing an overview of subterranean habitats, focusing on caves, and the major constraints cavefishes must overcome to live in such environments in complete darkness with limited food resources. We then provide an overview of taxonomic diversity and geographic distribution of cavefishes with a brief discussion of syntopy of cavefishes in subterranean habitats. Next we summarize what is known about the physiological, behavioral, and morphological adaptations that have evolved in cavefishes in response to the primary physicochemical and ecological stressors in subterranean habitats. In particular, we focus on adaptations associated with nonvisual sensory modalities. Finally, we offer a few suggestions for avenues of future research in cavefish adaptation and sensory evolution.