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Title: Factors affecting Bimodal respiration in the catfish Corydoras aeneus

Abstract: The catfish, Corydoras aeneus is an organism that respires bimodally , that it is being capable of drawing oxygen from both water and air. It carries out aerial respiration through it’s adapted posterior intestine.This experiment was done in order to determine the disadvantages of aerial respiration by manipulation of oxygen content and depth. The effect of dissolved oxygen, when the fish was placed into a cylinder of water and the oxygen concentration was determined while the number of breaths in a 10 minutes period was counted and recorded. Within the 10 minute period, three 15 seconds reps were used to observe the number of opercula beats. The
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There are various factors that show that aerial respiration is more favorable as it is energetically less costly than aquatic respiration where to acquire the same amount of oxygen the organism expends at least 10-20% more energy, such factors are that air has a higher oxygen content, faster rate of diffusion and is less dense than that of dissolved oxygen. However, only in cases of low levels of dissolved oxygen content does Corydoras aeneus use aerial respiration. Therefore, showing that there may be reasons to why it does not constantly carry out aerial respiration, even though it possess physiological adaptations to reduce disadvantages, thin respiratory surfaces and streamlined bodies.

Materials: one liter cylinder, oxygenated aquarium water, nitrogen gas, oxygen gas, oxygen meter, (1)Corydoras aeneus.

Method: To test the effect of dissolved oxygen, 500ml of oxygenated aquarium water was filled in a 1 litre cylinder where the oxygen concentration was taken. A Corydoras aeneus, catfish was then placed in the cylinder and the number of breaths was observed and recorded at a given time period of 10 minutes. Where, within the 10 minute count 15 seconds x 3 times was used to observe the number of opercula beats this was recorded. Nitrogen gas was then bubbled into the water in the cylinder to lower the oxygen content to approximately 4mg/L. The number of breaths and opercula beats per hour were
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