4 Cold-Climate Fish Selection Strategies

4 Cold-Climate Fish Selection Strategies

Keeping up our trek through the list of aquaponics winterization techniques (in no particular order), this week we turn to fish selection. This post will walk through the issues involved in selecting fish for cold climates.  Next time we’ll cover the economics involved.

  • Passive Solar Greenhouse Design
  • Insulated and Air-Sealed Fish Tanks and Grow Beds
  • Insulated Piping
  • Multiple Layers of Thermal Protection for Plants
  • Fish Selection for Cold Hardiness
  • Plant Selection for Cold Hardiness and Freeze/Thaw Tolerance
  • Efficient Water (Not Air) Heating
  • Programmable Temperature-Dependent Pumping Controls
  • Strategies for Maximizing Nitrification in Cold Water
  • Aquaponics-Integrated Hot Tubs (Seriously)

Winter Fish

“My old grandmother always used to say, Summer friends will melt away like summer snows, but winter friends are friends forever.” ― George R.R. Martin

Sitting in the warm greenhouse while the wind whistled by outside last winter, I did some fish thinking and some fish math.  I wanted to figure out the best way to get the most value out of my fish tanks with the smallest amount of inputs.  I came up with four options for what to do with my fish when it gets cold.

  1. Shut the system down.
  2. Harvest your warm water fish and switch to cold water fish.
  3. Raise fish that can survive both warm and cold water, year-round.
  4. Breed fish yourself, indoors in the winter.

Each choice offers benefits and drawbacks.  We’ll discuss them each here briefly.

Backyard Aquaponics Greenhouse in Madison

Shutting Down

Travis Hughey of Barrel-Ponics fame goes this route. 

Shutting down the system offers probably the simplest option.  If you shut down for winter, you don’t need to insulate or air seal your system as thoroughly.  You don’t need to shovel the path out to the greenhouse after every snowfall.  You cut one of your biggest expenses (heat) by at least 50%.

The negative consequences for winter shutdown include missing out on succulent winter spinach, several months of lost fish growth, an inability to raise fish which take multiple seasons to grow out, and the requirement that you re-introduce the nitrogen cycle in the spring. 

I should note that, if you live where it drops below 70°F at night and you don’t have a well-insulated or air-sealed system, you will likely still have to heat your water because evaporation robs a great deal of heat even in the warmer months.

Thermal Zones in an Aquaponics System

Harvest and Switch

Last winter, I chose this option for my aquaponic system.  In early October when night-time temperatures first hit freezing, I harvested all my tilapia from the freezer fish tank for the freezer-freezer and drove to my local hatchery for some rainbow trout.  In early June I harvested the trout before the heat of summer set in.

The advantages to switching fish include maximizing the fish harvest from your system, getting a different flavor of fish in your diet, and maintaining a high level of nitrates in your water for vigorous winter plant growth if you can maintain sufficient leaf zone temperatures.

Disadvantages to the fish switch include increased costs of larger stock (you must buy bigger fish in order to grow them out in six months), regular water changes if your plants don’t take up enough nitrates (I change 1/3 of the water each month), the need to run lights a few hours a day if you want strong growth in December and January when the days run short, and the requirement to heat the water to near 80°F to grow out tilapia in one season.

One false disadvantage that many warned me about is that “trout are finicky.”  While they do require high dissolved oxygen levels, reducing the temperature of the water allows oxygen to dissolve more readily and aerators don’t cost that much to buy or operate.  Supposedly trout also require a higher level of water quality, but I did not find this to be true.  With nitrate levels surpassing 150 and lots of solids floating in the water, I lost a grand total of zero trout this winter due to water quality.

Another issue I had worried about was nitrogen conversion rates.  At 50°F, according to the books, nitrifying bacteria begin to go dormant.  Again, not for me.  I checked in with the bacteria regularly through the winter and – to my relief – never found a measurable amount of ammonia.  I use flood and drain media beds, so I can’t speak for deep water culture which might require more filtration or the addition of some kind of media to provide the bacteria surface area to live on.

Year-Round Fish

Some fish types survive in both cold and warm water.  These include perch, catfish, and largemouth bass. 

In addition to raising trout this winter, I also raised catfish in a separate tank. This worked well because with my 50°F water temperature they added little to the nutrient load but will be grow quickly come warm weather.  

Aquaponic Fish Types

Within this option, you get three additional choices: 

  • Allow your fish to lose weight in winter with 35°F water (as they would in the wild).
  • Heat the tanks to the moderate temperature of 50°F and experience minimal growth but no weight loss.
  • Heat to 65°F which allows your fish to gain a reasonable amount of weight over winter.

Advantages to year-round fish include the option to purchase fry or fingerlings for less cost than larger fish, the ability to grow more fish types including perch (considered by many the best tasting freshwater fish), a reduced nutrient load requiring fewer or no water changes in winter, and the option to raise them together with other summer- and winter-specific fish if you have multiple tanks or compatible breeds.

Breed Yourself

Cozy nights by the fire, red wine, and a general slowdown of the pace of life in winter make us all want to breed… fish. 

I cannot claim any experience with breeding, but I do know that it offers one major benefit.  If you do it right, you don’t have to purchase fish at all except to widen your gene pool.  For me, driving to hatcheries and purchasing fish makes up the largest yearly cost of running my aquaponics system.  With breeding, the cost savings are substantial. 

Disadvantages to breeding indoors include a limit to the types you can breed yourself, the requirement for indoor breeding tanks, the noise of an aerator when you want to sleep, and the potential for mold in an over-humidified room.  If you breed tilapia, this requires you to either purchase or produce a super-male (yes, that’s a real thing) or make do with slower-growing mixed-gender stock.

As possibly the simplest breeding solution, raising mixed-gender tilapia together with largemouth bass allows the tilapia to breed prolifically (as they do) and the bass to eat all their fry.  When you want more tilapia, you simply take a few fish into a separate tank and allow them to breed for a time.

The next technical post will go over the economics of these different choices.  Stay tuned!