Tunas have elevated levels of ion and water transfer due to their elevated gill and intestinal Na+/K+ ATPase activity, in which this activity is estimated to be about four to five times higher when compared to other freshwater vertebrates, such as rainbow trout. The gills, due to their large surface area, play a significant role toward osmoregulation in the tuna to maintaining water and ionic balance by excreting NaCl. The intestine also contributes toward compromising for the osmotic loss of water to the surroundings by absorbing NaCl to withdraw the needed water from the lumen contents.