Trading Rainbow Trout for a Better Mousetrap

I’d dreamed of having the first rainbow trout farm in Laos. That’s part of the reason I chose to lease my little coffee plantation with the waterfall on the Bolaven Plateau at 1,200 meters above sea level. So, it’s hard for me to give them up in this unrelated yet still sort of related project I’m considering in frozen New England. But trout are troublesome. The determining factor was water temperature and its relationship with microorganisms. The latter just won’t be as happy as the trout at 16 to 18C (60 to 65F). Swallow hard and accept that, then all sorts of possibilities come up. I was lucky to get advice from a professor at the University of Hawaii. He suggested the cold-tolerant blue tilapia. Cool, I thought, I just killed 750 of their relatives, the more common Nile tilapia.

Blue tilapia will survive in far worse water conditions than rainbow trout

This photo, courtesy of Aquaponics USA, reveals the blue tilapia to be a hardy-looking if not attractive fish. Blue tilapia are mouth-brooders, meaning the females keep their eggs and fry in their mouth until they are able to take care of themselves. And they are essentially fry producing machines. I already know a lot about tilapia, especially how to kill them, so I’m now very comfortable with this decision (I mean to raise them, not kill them prematurely). This means I can bring the system water temperature up to 21 to 24C (70 to 75F). Sure, this will require more propane, but I’ve come up with some additional ideas on insulation and the design of passive solar water heating/solids settling tanks.

With blue tilapia, I don't need to worry about accidentally overheating the system water

To ease the expansion of the system in the fall and the ultimate dismantling of it in the spring, I’ve decided on maintaining a series of independent aquaponic production lines. Each would have a fish tank holding about 1,000 liters (260 gallons), a hydroponic trough of about 5.6 square meters (60 square feet), and a passive solar heating/solids settling component holding about 500 liters (130 gallons) now located outside of the enclosure in its own insulated box. I would stock the first tank with 50 blue tilapia fingerlings and wait for them to create more fry (about 1 month). I would divide these fry into two cohorts in the second and third tank. At that point, so as not to be up to my ears in tilapia fry, all the tanks would get a false bottom, a screen, to prevent the female tilapia from picking up their eggs off the bottom. They could then concentrate on growing (the main reason why female tilapia grow more slowly than male tilapia is due to all the time they spend mouth-brooding and not eating).

With three production lines up, I would focus on keeping track of the water heating costs and the environmental conditions inside the enclosure throughout the winter. I’ve estimated the costs for this system as follows:

  • Fish tanks– Used 275 gallon (1,045 liter) IBC @ $105 x 3 = $315
  • Solids settling/passive solar component– Recycled closed head steel drums @ $16 x 9 = $144
  • Wood for ceiling panels– 2 x 4 x 8′ pressure treated lumber @ $2.77 x 72 = $200
  • Rigid insulation board for ceiling panels– 12 sheets @ $10 = $120
  • Posts for ceiling support– 2 x 4 x 8′ pressure treated lumber @ $2.77 x 9 = $25
  • Burlap roll– $65
  • Wood for hydroponic troughs– 2 x 4 x 8′ pressure treated lumber @ 2.77 x 36 = $100
  • Wood for hydroponic troughs– 4′ x 8′ pressure treated plywood @ $27 x 5 = $135
  • Wood for sumps– 2 x 6 x 8′ pressure treated lumber @ $5 x 6 = $30
  • Bathroom exhaust fan– $14 x 3 = $42
  • Greenhouse plastic– $98
  • Assorted plumbing materials– $100
  • Pumps– Laguna Max Flo 600 (about 1,000 LPM at 90cm head) @ $82 x 3 = $246
  • Aeration– Hydrofarm AAPA45L 20-Watt 45-LPM @ $38 x 6 = $228
  • Raft material– Dow Styrofoam 1.5″ blueboard @ $30 x 6 = $180
  • Straw bales– 160 @ $2 = $320
  • Tankless water heater– EZ101 = $145
  • Propane regulator– $25
  • EZ sediment filter– $25
  • EZ service valves– $135
  • Propane tanks– @ $30 x 2 = $60

A total of eight 3-trough systems could fit in my brother's greenhouse for 1,440 square feet of raft area

The total is $2,738 not including fish, crayfish, lettuce seeds, etc. An excellent source of information about year-round aquaponics in a greenhouse (in their case, a renovated one) is Colorado Aquaponics. Their system is a community-scale one which provides consumers in their otherwise “food desert” with fresh produce all year. They have 1,200 square feet of deep water culture rafts which could produce more than 20,000 pounds of lettuce per year. That’s 16.66 pounds per square foot. That means the system shown above can produce more than 3,000 pounds of lettuce per year, or about 60 pounds per week. If production in the system were geared towards mesclun and spring mixes, according to a Vermont study comparing retail prices at farmers’ markets and grocery stores, a pound of produce is worth between $5.83 and $9.64. Taking the median of $7.74 per pound, that’s $464 per week. Essentially, the above costs would be paid for after 6 weeks of full production. I could carry on counting the proverbial chickens, but I think it’s clear that there is a fairly robust potential return on investment. If one were to really count his chickens before they’ve hatched, consider how many of these systems would fit into my brother’s greenhouse. Yup, 8 systems. That would produce 480 pounds of mesclun a week worth $3,715. That’s close to $200,000 a year. And, by the way, since we’re using blue tilapia instead of rainbow trout, the whole thing could be easily moved outdoors while the existing greenhouse is doing its thing. I’d say that’s a fair trade for the rainbow trout.




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