Morphological differentiation in the widespread fish Galaxias maculatus: Do darker environments imply bigger eyes?

JAVIER ROJO; PATRICIA RODRIGUEZ; CLAUDIA BOY

HYDROBIOLOGIA

SPRINGER

Lugar: Berlin; Año: 2020

0018-8158

The visual capacity of aquatic organisms is in general related to light penetration in the water. Therefore, aquatic environments that differ in color can potentially contribute to species polymorphism, especially in fish. In this study, we explore the relationship between light quality and intensity in water bodies and the eye size in Galaxias maculatus, one of the most widespread fish in the area. Fish morphology was studied photographically, and the vertical attenuation coefficient of light (Kd) was measured in five aquatic systems: two humic lakes, two estuaries, and one river. Water color was also estimated as absorbance at 440 nm. In those environments with less light penetration and darker water color, we observed bigger eyes and additionally, larger mouths. The darkness of water bodies was mainly related to water color associated with humic substances. As G. maculatus is known to be a visual predator, our results suggest that bigger eyes increase visual capacity in darker environments, which would result in improved feeding rates, also supported by larger mouth length.