The southern bluefin tuna have a large gill surface area which is important for oxygen consumption and handling high osmoregulatory costs, associated with the high resting metabolic rate. They can adapt to increasing water salinity, where the ionocyte increase in size, gill filaments become thicker, the surface area of the basolateral memebrane increases, and the intracellular tubular system proliferates. Teleost fish do not have the loop of Henle in the kidneys and are, therefore, not able to produce hyperosmotic urine. Instead, they secrete small amounts of urine frequently in order to prevent water loss and excrete NaCl thorough the gills. Additionally ram-ventilators such as tunas and billfishes have specialized gill structures: adjacent lamellae and filaments are fused to prevent gill filaments and lamellae from collapsing under high water flow. Here, ionocytes have also been found on these specialized interlamellar, lamellar, and filament fusion in larval and adult Yellowfin Tuna ("Thunnus albacares").