 The result is a net movement of water into the fluid of the bluefin tuna, with the net movement of ions being into the seawater.Southern bluefin tuna, along with other marine teleost fish, have acquired a variety of proteins and mechanisms which allow the secretion of ions through the gill epithelium.Due to the southern bluefin tuna's high metabolic need, ions must be taken up relatively quickly to ensure sufficient concentrations for cellular function.