Other ions absorbed by the gill tissue include calcium, lithium, cobalt and strontium. The absorption of these ions may be necessary to replace salt losses or to supplement minerals in the diet. Thus the gills also function to maintain salt and water balance, a process known as osmoregulation. Because of this duel function of the gills, they are acutely sensitive to changes in water quality. Factors such as temperature, pH, salinity and dissolved oxygen and carbon dioxide affect the function of the gills.
Gill tissue is the most permeable of the tissues.
In gill tissue, oxygen from the water need only pass across one cell before being picked up by red blood cells. This delicate organ that performs such vital tasks is most sensitive to stressors. It is the design of the gill that makes them so efficient, but also makes them more susceptible to damage. If we examine gill tissue under the microscope, we see feather like structures called lamellae. These lamellae provide a large surface area for exchange of oxygen and carbon dioxide.