Gerbil Test Tank
The respiratory exchange ratio (RER) is the ratio between the amount of oxygen (O2) consumed and carbon dioxide (CO2) produced in one breath.  This needs to be determined for test subjects. Since it's planned to put a mouse or something with four legs in the biosphere IV, it needs to be determined if the marine ocean section can handle the CO2/O2 load. Not only does the animal throw out CO2, but its poop and the (pre) rotting food it does not eat at the time. Â
It's better to do a rough calculation of the gas cycle(s)Â before spending a lot of time, money and energy on building a system that will fail. Â It is better to take out as many variables as possible while building systems. Â It's understood how to sink CO2 and produce it in any quantities, but loading down the system is not understood. Â This test tank is used to answer the questions for designing a farming tank(s).
Goals:
- Find the RER for a gerbil.
- Observe daily habits for creating an environment where the gerbil will not tear up everything in the farming chambers.
- Determine eating habits (which plants the gerbil eats and record weight gain or loss)
- Determine how much CO2 is thrown by poop and pee.
- Determine the number of plants and their growth habits. Â (this explores how many plants need to be moved away for recovery before presenting the plant back to the gerbil)
- Train gerbil to eat through foraging. Â (Since the farming chambers are small and not easy to access without breaking seals for exchange of gasses to the outside, it's easier to let the animal do what it does naturally and build the environment to help it.)
Test/Designing Method Description
The test is simple and will take a few weeks to a few months to complete. Â The test is performed in three stages:
- Build the tank where all instrumentation is in place and determine the RER.  It should be completed in less than 48 to 72 hours.  Afterwards the system can be opened to the air.
- Experiment with presenting food(s) to the gerbil as cut and as attached to the plant. Â Monitor gerbil weight.
- Build habit for gerbil where it naturally lives in. (condition/train the gerbil to harvest its own food - drink water out of a pool)
The tank is a 40 gallon fish breeder tank.  There is a screen where the pee and poop falls through and can be measured for weight.  The top of the tank is sealed for the first test.  Later, a glass plate is used to allow light for plants to grow.  Daylight list 12 hours on/ 12 hours off.  Screens are not used because they can block up to 50% of light.
CO2Â and DO meter is placed under the screen. Â CO2 is heavier than air, so it will sink to the bottom. Â The DO can be measured anywhere above the CO2 layer.
Water is provided for the gerbil with water in a pool/bowl, not from a SS tube attached to a bottle.  All plastics are removed.  Water is only presented in this fashion in the biosphere.  Â
All glass walls, containers and equipment is wiped down with isopropyl alcohol before conducting the test. Â It's been known for bacteria attached to walls and equipment swinging results. Â And the gerbil will not be wiped down. Â It brings in what it has. Â In most cases (when it comes to worms and insects), they contain all of the bacteria and animals to help with their decomposition/construction life cycle.
Respiratory Exchange Ratio
In general the RER is around 0.8 (O2/CO2) at rest.  If it goes higher, we are consuming food we just ate.  Anything higher than 1.0 is consuming energy for movement.  Anything lower than 0.7 is consuming stored energy.  This is calculated by measuring the amount of dissolved O2 and CO2 over 24 hour period.  It needs to be for hours and averaged.  Sometimes these kind of experiments take a day to two for stabilizing  the bacteria on the walls of the tank.
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