Benthic fish exhibit more plastic crypsis than non-benthic species in a freshwater spring

Abstract

Cryptic coloration reduces the ability of predators to detect prey, but the plasticity of this defense varies. Some organisms possess static and permanent cryptic coloration, whereas in other species color changes may be induced. Depending upon the species, induced color changes may be reversible or irreversible. In this study, we examined a subtle, rapid, and reversible crypsis in which small fish exhibit muted changes in brightness to match varying substrates in clear spring water. In the laboratory, we visually measured the changes in brightness, using a ten-point brightness scale, of five abundant small species in our study spring. Two species, Lucania goodei and Heterandria formosa, exhibited no change, but the other three species exhibited changes in brightness to match background brightness. Two species, Gambusia holbrooki and Poecilia latipinna, exhibited only slight shifts, whereas Lucania parva exhibited relatively large shifts in brightness and color pattern—from virtually white to tan interspersed with dark-brown bands. In the field, L. parva also exhibited significant shifts in brightness and color pattern, both when swimming freely and when enclosed in an open-bottomed cage. These results suggest that rapid cryptic changes in brightness may augment other forms of defense in small vulnerable fish.