The Corydoras aeneus carries out the process of bimodal respiration, hence once the dissolved oxygen concentration in water decreases it uses oxygen in the atmosphere, switching from aquatic (the use of gills) to aerial (the use of a posterior intestine) respiration. This lab was executed to determine the effects of dissolved oxygen concentration and depth on the frequency of air breathing in Corydoras aeneus. For both conditions the surface breaths per hour and opercular beats per minute were recorded by counting the number of breaths and beats every 15 seconds. Two graphs were plotted and interpreted. It was seen that with a decrease in dissolved oxygen concentration there was an increase in aquatic respiration. It increased from an average beats per minute of 136.7 at an ambient oxygen concentration of 7.01mg/L to 174.4 beats per minute at oxygen concentration of 2.99mg/L.  In this examination the catfish did not utilize aerial respiration. With increasing depths, the catfish began to respire aerially, hence reducing its aquatic respiration, a switch in respiration was seen and this caused the lines on the graph to intersect. It decreased from an average beats per minute of 152 at a depth of 8cm to 137.6 beats per minute at a depth of 25cm, with intersections at approximately 17cm and 22.5cm. These graphs were significant because it clearly displayed the switches from aquatic to aerial respiration, had 48 breaths per hour. Aquatic respiration is the primary mode however, different factors causes it to respire aerially, like depth.

Bimodal respiration refers to an organism’s capacity to utilise both air and water as respiratory media to obtain oxygen. This allows the organism to respond differently to changes in the dissolved oxygen level of the water. The is a compensatory method for hypoxia, as it aids in allowing the fish to withstand harsh levels of oxygen deprivation by allowing an alternate route of obtaining oxygen to meet its respiratory needs for survival. Generally, a low dissolved oxygen level, will cause the fish to increase its use of atmospheric oxygen. This experiment is being done to determine at which point the switch from aquatic respiration to aerial respiration will occur. (1980 by Donald L. Kramer). Aquatic respiration occurs as the organism intakes oxygen

rich water from the environment to absorb oxygen into its blood stream to transport the oxygen to the rest of the tissues in the body, while removing the excess carbon dioxide and expelling it through the operculum. As a result, water is essential for gaseous exchange in these respiratory systems, as it aids in providing a concentration gradient essential to allow diffusion. Organisms that respire using aerial respiration rely on blood systems for gaseous exchange and transport.

A greater outflow of energy is required when oxygen is extracted from water in comparison to air. This extraction is executed by several respiratory organs such as gills. In most fishes the gill is the main respiratory organ used and it consists of gill filaments which provide the surface area for efficient gaseous exchange. Fish have evolved a way to overcome their oxygen-deprived environment through their highly specialized gills. The gill is where fish absorb oxygen from the surrounding water into their blood. However, oxygen can only diffuse into the blood at the gills if the oxygen level is higher in the water than in the blood – that is, oxygen needs to flow from an area of high levels to an area of low levels. Fish gills use a design called ‘countercurrent oxygen exchange’ to maximize the amount of oxygen that their blood can pick up. They achieve this by maximizing the amount of time their blood is exposed to water that has a higher oxygen level, even as the blood takes on more oxygen. Countercurrent oxygen exchange means the blood flows through the gills in the opposite direction as the water flowing over the gills. (FISHBIO. 2015)

The Corydoras aeneus is an intestinal air breather that uses their posterior intestine for aerial respiration. Ventilation in this fish happens when they take gulps of air from the surface of the water. Oxygen is taken into the mouth and expiration through the anus as the fish begins to dive. (L.Donald 1991)The catfish have the capability to use oxygen in the air using their posterior intestine as an additional respiratory organ. It is modified into a high vascularized and thin-walled structure which occurs because of the epithelium reducing in thickness along with the muscle and submucosa layers. These cause a reduction in the diffusion barrier which makes the process of gas exchange more efficient. However, it is unfit for digestive functions. (Carter and Beadle, 1931; Persaud 2000)

 

Objectives: -To examine the effect of dissolved oxygen concentration on the frequency of air breathing in Corydoras aeneus by counting its number of surface breaths/hr and opercular beats/min.

-To examine the effect of depth on the frequency of air breathing in Corydoras aeneus by counting the number of surface breaths/hr and opercular beats/min.

Method: As in handout.

Results:
Carter Gs, Beadle LC, 1931. The fauna of the swamps of the Paraguayan Chaco in relation to its environment. II. Respiratory adaptations in the fishes. J Linn Soc Lond Zool 37:327-368

Donald L. Kramer, Martha McClure. 1980. "Aerial respiration in the catfish, Corydoras aeneus Can. J. Zool., 1980: 1984-1991.

FishBio. “An Efficient Exchange: Countercurrent Oxygen Exchange in Fish.” FISHBIO Fisheries research monitoring and conservation. Fisheries Research, Monitoring, and Conservation, October 27, 2015. https://fishbio.com/field-notes/fish-biology-behavoir/an-efficient-exchange.

HOWBLL, B. J., BAUMGARDNER, F. W., BONDI, K. & RAHN, H. (1970). Acid-base balance in coldblooded vertebrates as a function of body temperature. Am. J. Physiol. ai8, 600-606

Wade, Edwin. “Respiratory System- A Quick Tour General Function Aquatic Systems Land Systems Insect Amphibian Mammalian. - Ppt Download.” SlidePlayer, 2016. https://slideplayer.com/slide/4463135/.