Marine teleosts also use their gills to excrete osmolytes (e.g. Na⁺, Cl−). The gills' large surface area tends to create a problem for fish that seek to regulate the osmolarity of their internal fluids. Seawater contains more osmolytes than the fish's internal fluids, so marine fishes naturally lose water through their gills via osmosis. To regain the water, marine fishes drink large amounts of sea water while simultaneously expend energy to excrete salt through the Na+/K+-ATPase ionocytes (formerly known as mitochondrion-rich cells and chloride cells). Conversely, fresh water less osmolytes than the fish's internal fluids. Therefore, freshwater fishes must utilize their gill ionocytes to attain ions from their environment to maintain optimal blood osmolarity.