Turbid waters don’t pose the only visual challenge for fish. Some fish have found their niche in environments seldom explored by other animals. Cave-dwelling organisms also face the difficulties posed by the lack of sunlight. Blind cave tetras (Astyanax mexicanus) hail from freshwater cave systems of Central America, and are just as adept without eyes as sighted fish. To save on the energy of developing eyes, and pigment that no other organism is likely to witness in its natural habitat, these fish have done away with both! They navigate their environment by using their sensitive lateral line. Specialised detector cells that form two lines running down either side of their body (a feature possessed by all fish to a greater or lesser degree) can detect differences in pressure in the water. This is analogous to our sense of hearing, where we can detect differences in air pressure or sound. These fish are effectively hearing their way around their environment!
Image credit: H - J Chen
Tagged in: Aquatic Adaptations