In dark, sight can be costly, novel measurement finds
Eyes and the brain tissue needed for vision demand about 15 percent of the energy budget of a young Mexican fish, researchers have found. This hard-to-discover percentage supports the idea that energy cost-cutting helps explain how cavefish go blind.
That 15 percent represents a notable energy demand for a 1-gram juvenile Mexican tetra fish (Astyanax mexicanus) at rest, says fish biologist Damian Moran of Plant and Food Research in Nelson, New Zealand. Brain tissue for vision and eyes could therefore become a liability in food-sparse caves, where no sunlight supports energy-catchers such as plants, Moran and colleagues argue September 11 in Science Advances.
The energy cost is greater for juvenile fish than for older ones, the researchers say. As fish grow, their bodies enlarge more than their brains do. By the time a Mexican tetra reaches 8.5 grams, vision demands only about 5 percent of