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LAB 25 - Respiration and Metabolism in Trout


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The purpose of this lab was to determine the oxygen consumption rate of steelhead trout

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j0282780.gif (4858 bytes)Procedure
We had to first calibrate the electrode to 100% air saturation by immersing it in aerated water and adjusting the oxygen electrode meter to 100%. Then we had to set the meter switch to the ZERO position and adjust the meter to 0% air saturation. After calibrating the electrode and adjusting the meter, we filled the plexiglas chamber with aerated water and connected it to the pump. When the chamber was all connected and ready to go, the next step was catching the fish and getting him into the plexiglas chamber. After getting are fish into the camber we sealed it up and then completely filled the chamber to the top using a funnel, which was inserted, through the top of the chamber. When the system was as full as we could get it, with the least amount of air bubbles the plug was inserted and the pump was started. The timer was then started. The O2 meter reading at the time that the timer was started was 80%, so we allowed are fish to respire until the meter read 40%. This was half of the total percent, and is usually the point when the fish will become distressed.

j0282780.gif (4858 bytes)Data
The data that we were required to collect was, the weight of the fish, the volume of the water that we put into the system, the temperature of the water, % air saturation at time zero, % air saturation at end of run. The data for my group was as follows:

Weight of the fish = 57.5 g
Volume of water = 400 ml
Temperature of the water = 20EC
% air saturation at time zero = 80% at time 12:46
% air saturation at end of run = 40% at time 12:50 and 50sec




Calculation of VO2 - You have to calculate the oxygen content of the volume of water in the system when it is 100% air saturated. In order to do this, you need to be familiar with Bunsen solubility coefficients for oxygen in fresh water (ml (oxygen at STP)/ml of water saturated with air). The values are listed in this table.

5 C



10 C



15 C



20 C



The amount of O2 consumed by the fish is 50% of the O2 dissolved in 400 ml of FW 100% air saturated at 20 C. Looking at the table above, you see that 400ml of fresh water under these conditions contains 6.2 ml of O2 (STP). The fish consumed 50% of this or 3.1 ml.

Time taken to consume the 3.1 ml of O2 was 4 min and 50 sec (approximately equal to 5 min). In 1 hr, this would be 3.1 x 12 (60min/5min = 12) or 37.2ml/hr.

Since VO2 values are commonly expressed as ml/hr*g, we had to divide by the weight of the fish: (37.2ml/hr) /(57.5g) = .647 ml/hr*g.

Calculation of the metabolic rate - (.647ml/hr*g) x (4.8) = 3.11 ml/hr*g.

Summary - endothermic animals require a faster metabolic rate than those animals that are ectothermic. Smaller animals also tend to have a faster metabolic rate than larger ones because of surface to volume relationships

j0282780.gif (4858 bytes)Equipment

Oxygen Electrode Meter

The O2 meter does two things. It applies a voltage of about 0.2V between the electrodes, and measures the current generated by the oxygen redox reaction.

Respiration Chamber

Used to contain the fish while measuring the VO2 rate.

Polargraphic Oxygen Meter

The oxygen electrode consists of an insulating epoxy rod containing two electrodes, a cathode surrounded by an anode. This electrode is covered by a thin teflon membrane through which oxygen can diffuse from the solution being measured. Two things about an oxygen electrode, to be accurate the temperature must be constant and the measured solution must be stirred.

See a brief demo of this lab.