Critter Farming
(or ensuring a supply of protozoa during the fallow season!)

by Mike Andre, USA



Over the years I believe I've tried most methods available in order I might have 'cultures' of protozoa and metazoa (hereinafter referred to as 'Critters') available year round (being in the northern tier of the United States, winter take its toll and makes it difficult, if not impossible, to obtain samples from ponds, lakes and streams.)

Aquaria of various sizes and shapes, with/without aeration, artificial sunlight, covered/uncovered – no matter what I tried, eventually all went dormant. For the avid microscopist this often results in withdrawal syndrome – the hands shake, eyes flutter and anything/everything that isn't attached permanently to someone threatening permanent physical damage becomes grist for the mill, (specimens for the stage.)

In the spring of 2005 I was determined to take action to avoid my coming up dry, so to speak, the winter of 2005/2006.

After discussing this situation with a number of people and doing a fair amount of thinking, I realized colleagues and acquaintances who had a tank or trough outside always seemed to have decent populations of critters. Several respondents specifically mentioned horse or stock watering troughs, (regular inoculation and introduction of food stuff when the animals drink.) This started to make a lot of sense; natural inoculation (animals, precipitation, wind, whatever) as well as significant mass to dampen swings of temperature or pH.

Not being one to tarry when inspiration (or anything similar) strikes me, it was off to the local farm supply store, where I found a heavy gage plastic stock watering tank, approximately 28” wide X 13” deep (71 cm X 33 cm) with a capacity of 25 gallons (95 liters.) After positioning the trough at the wood line of my property, I trekked down to the creek (or if you're originally from the area of Philadelphia - 'crick') in the valley on the back of the property and managed to get several buckets of stream muck, leaf litter and rocks as the initial biomass and base for the trough. This was followed by buckets of creek water. I figured there was nothing left for me to do but wait a bit, perhaps a few days or weeks, and then pull a sample and enjoy the results.

Soon to be 'Critter Farm'

I overlooked a few minor things:

Mosquitoes love the idea of standing water – makes a perfect mosquito hatchery! Within a few days there was a plentiful supply of 'wigglers' A.K.A. mosquito larvae in the critter tank. While these provided an interesting diversion under the scope, I am just sensible enough to know my popularity with the important half of my marriage would be in jeopardy if she were to discover I was growing my own crop of blood-sucking mosquitoes, and less than 50 meters from our back deck!

Nothing is ever simple – after some discussion with the people having the horse and stock watering troughs, I learned they neglected to mention they usually keep a few goldfish in the tanks to control the mosquito larvae population. It seemed a simple solution; all I needed is some 'goldfish' – so off to the pet store went my 'gofer-at-large' otherwise known as my wife, with instructions to purchase several goldfish.

Upon her return she handed me a plastic bag with twenty (20) small fish! I asked why she bought so many and was advised the pet store was 'out of goldfish’ - can you believe that? How on earth can a pet store run out of goldfish? Anyway, she bought what they call 'feeder fish' which is another name for small goldfish even though most of them were various shades of black and brown (Hey! What do I know?) and they sell them at US$1.00 for 20. Evidently these are purchased by people who own predator fish that require live food. Unceremoniously the fish were put into the tank (after letting the water temperatures come to equilibrium by floating the plastic bag in the tank for a few hours.) I figured they would come to stasis without my involvement – the available food supply would feed so many, and the others would contribute to the biomass of the tank.

Sure enough, in less than two days the wigglers were nowhere to be found! After a week or two the fish population seemed to level off around eight or so (I never have been able to get a good census as they dart away and hide whenever I approach!) I think the decrease in the fish population may be a direct result of several neighborhood cats thinking I've placed these fish out there as appetizers.

The wigglers were in control and all was right with the world – right? Wrong!

I realized I had created yet another problem - I like to think ahead and even though it was June at this point, I was anticipating the advent of winter and the inevitable impact freezing solid would have on the goldfish/feeder fish. Temperatures here can get to well below 0° F (-18°C) for weeks at a time, and having experienced the aftermath of failure of a heater in a hot tub in mid-winter, I know we had the real possibility of a 25 gallon (95 liter) block of ice. Now protozoa and probably even metazoa can survive being frozen solid; goldfish cannot. As well, part of the project design was availability of critters year round, and having to hack a hole through whatever layer of ice didn't seem to fit the initial concept.

After some searching a solution one presented itself at the farm supply store from whence the tank first came – a 'stock tank heater.' These are used by farmers, ranchers , anyone who has large animals to insure the animals have fresh water available year round. The unit is nothing more than a resistance heater (various wattages available) with a thermostatic on/off control, all neatly done up in a waterproof package one just hooks up to the mains and drops into the stock tank. When the temperature drops below 35°F (2°C) the heater switches on brings the water up to ~40°F (4°C) when the thermostat kicks off again.

Of course all these things come with a price, and I am starting to wonder how much money I'm willing to spend to grow protozoa! Was it worth it?

Yes! Within the first few months I was gratified beyond expectations with varieties and numbers I never expected nor experienced before. Many species new to me were evident in the tank, and I was constantly surprised at the fecundity (one doesn't get to use that word too often, and when the opportunity presents itself, well.....) of the critter trough. I was really concerned it would “burn itself out,” but not to worry! Each time I took a sample new critters were evident. (After typing this, I wonder if “burn itself out” wasn't a Freudian slip.)

In the throes of winter I kept peering out the back windows trying to ascertain there was 'open water' in the critter tank, and yes, there was, until that fateful day............ Looking out it appeared there was solid ice cover on the tank. Trudging out through the accumulated snow, (~two feet/60 centimeters by this time) I realized the three year warranty on the stock tank heater was about be tested. Off to the farm supply store (they are beginning to address me by my first name, demonstrating I've been visiting too often!) and a replacement (higher wattage) is secured.

I think there are many reasons why this tank has succeeded, not the least are size, location and continual natural inoculation via a variety of routes, including precipitation (rain/snow/whatever) wind-borne cysts and eggs and very likely some involvement of the local fauna that could include everything from birds and deer to raccoons, opossum, skunks, foxes, and whatever (probably local domestic animals as well.) It should be noted no water is added other than natural additions from precipitation. Yes, the level gets pretty low during long periods of summer heat with no rain, but due to the depth it has never approached anything less than one third full.

It has been a great pleasure to grab a small sample from the trough, pop a slide on the stage and be rewarded with microscopic life forms in abundance, the varieties changing with the seasons.

One of the things I'm still trying to figure out: bringing in samples and even filling aquariums with water from the tank will only provide viable cultures for a few days to a few weeks, while the critter trough continues producing without a hitch.

In conclusion, I would say the Critter Trough has been a success – the supply of protozoa has been without interruption and more varied than I could have hoped for. Maintenance is almost non-existent, and I expect the diversity and density will continue as the tank ages and 'ripens.'

On that note, there have not been any noticeable odors emanating from the tank, and I'm sure the neighborhood fauna has come to depend on the water supply. It is now coming up on one year since the critter farming adventure began, and I can commend it heartily.

Comments to the author Mike Andre are welcomed.


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