Plasticity in gill morphology and function

The fish gill has been optimized over millions of years of evolution to provide vital functions in respiratory gas exchange, osmoregulation, acid-base balance, and nitrogenous waste excretion. Despite a fairly consistent basic morphology, clear differences in gill size, thickness, and function reflect the varying physiological requirements of fishes living in diverse and sometimes challenging aquatic habitats. In many cases, the fish gill also shows the ability to adjust to changing environmental conditions in a matter of days to weeks. This article highlights trends in the plasticity of gill morphology and function on both long-term (evolutionary) and short-term (acclimation) time scales.