Bluefin tuna are amongst the most active fish meaning they need efficient respiratory and circulatory systems to supply their needs. A Bluefin swims with its mouth open, forcing water past its gills in a process called ram ventilation. Its gills have up to 30 times more surface area than those of other fish. Respiratory systems of southern Bluefin tunas are adapted to their high oxygen demand. Bluefin tunas are obligate ram ventilators: they drive water through their mouth (buccal cavity), then over the gills, while swimming. It is this movement of oxygenated water over the gills that allows the fish to stay alive. The Bluefin does not require a separate pump to produce a stream of water over the gills. However, when you compare this feature to other species of fish, separate pumps are present. Bluefin don’t need this pump system because it isn’t efficient enough to provide the volume of oxygen needed. This means that tuna must keep swimming to allow the water to pass over the gills to ultimately to prevent suffocation. The oxygen need and oxygen uptake of the southern Bluefin tuna are related. As the tuna increases its energy need by swimming faster, water flows into the mouth and over the gills more quickly, increasing the oxygen uptake. Tunas have highly specialized gills, with a surface area larger than that of other marine environment organisms. This increased surface area allows more oxygen to be in contact with the respiratory surface and therefore diffusion occurs quicker. Also it has a very thin gas-exchange membrane allowing the oxygen to diffuse a short distance across the respiratory surface to get to the blood. This allows the tuna to take oxygenated blood into the circulatory system more quickly. As well as this, the tuna’s uptake of oxygen from the water is a lot more efficient in comparison to other species of fish. The Bluefin tunas rate of utilization of oxygen has been recorded as high as 60% whilst other species typically utilize below this at roughly 27-50%. This is due to a combination of the large surface area of the gills and the short distance the oxygen has to travel. This means that oxygen can be supplied quicker enabling the highly metabolic organism to maintain an optimum temperature and energy for continuous swimming. This then allows the fish to continue its search for food to grow and reproduce and ultimately stay alive Ultimately the adaptations of the respiratory system compliment the Bluefin’s circulatory system which contains more haemoglobin, meaning the blood has a greater oxygen capacity. Comparing the Bluefin tuna's respiratory system with the human respiratory system When comparing the Bluefin’s respiratory system to that of humans there is a clear difference in the efficiency of the process. The tuna requires a much more efficient system because it gains its oxygen from a denser medium, water. Uptake of the oxygen from water must be effective because water contains less oxygen than air itself. Although the efficiency differs, they are the similar in the sense that their features greatly increase the surface area allowing for more efficient gas exchange by diffusion. Also both systems consist of thin, moist membranes to allow the movement of dissolved gases to pass into the blood. Another obvious difference would be the location of the respiratory organs, as in fish they are situated to the sides of the organism whilst in a human the lungs occupy the upper torso. A huge difference would be that the tuna requires movement to pass the water over the gills (ram ventilation), whereas in a human it is the contraction of internal muscles which alters the pressure in the lungs forcing air in or out. This highlights the need for the external environment to provide the movement for oxygen to be taken in for fish, in comparison to the internal environment of the thoracic cavity bringing about oxygen intake. Overall the two systems share the same purpose but have different adaptations due to differing environments. https://en.wikipedia.org/wiki/Southern_bluefin_tuna
http://link.springer.com/article http://ngm.nationalgeographic.com/2014/03/bluefin-tuna/superfish-interactive https://www.researchgate.net/publication/226448900_Cardiovascular_and_respiratory_physiology_of_tuna_Adaptations_for_support_of_exceptionally_high_metabolic_rates http://www.s-cool.co.uk/a-level/biology/gas-exchange/revise-it/gas-exchange-in-fish
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Ciara Branagan
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October 2016
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