Designing an Aquaponic Greenhouse for an Urban Food

to transplant young seedlings is when the first true leaves appear, usually 2 to 3 weeks after seeding.
However waiting until 4 or 5 weeks after seedling is very common in areas that have harsh winters.
Seedlings are started at the end of winter, then transferred as soon as conditions become favorable for
planting. (Blazich, 1999)

2.3.3.1.1 Marketability of Seedlings
In the year 2012 the State of Massachusetts generated $5,407,406 in revenue from Organic food sales.
(2012 Census Volume 1, Chapter 1: State Level Data.) Three agrichemical firms—Monsanto, DuPont, and
Syngenta—now control 53 percent of the global commercial seed and seedling market. As a result these
large companies have the leverage in the market to dictate the prices. More than 80% farmers will at
some point purchase seedlings for their land and find the prices of these commercial seeds and
seedlings very costly. (Bob, 2013) The seedling market window in Massachusetts is very narrow, the
winters prevent growth, so the viable time period is usually early spring up until late autumn.

The seedlings produced by the greenhouse will also have the advantages over seedlings from
commercial companies. Most organic seedlings travel less than 100 miles from their first source of
growth, while commercial seedlings travel between 300-500 miles from the source. (C, 2008) This
difference in distance greatly affects the seedlings, as they are likely to be damaged during excess travel,
especially before the plant has fully developed its structures to sustain itself. Local organic seedlings also
have a slight edge in marketability due to the stigma surrounding Genetically Modified Seeds. A
Genetically modified seed is one in which certain characteristics of the seed have been altered so that
the plant matures faster or produces larger yields. These modified plants have been linked with many
health related illness, especially digestive disorders, as our body has a hard time processing these foods
(Vendômois JS, 2009). The market for these organic seedlings is highly viable even though there is stiff
competition with commercial producers.

2.3.3.2 Comparison of Different Fish in Aquaponics
The team decided that a comparison of the three most commonly used fish in interior growing modules
would be useful for the design matrix. Our research showed that the best fish to grow within the system
was Blue Tilapia. When compared to the two other popular fish (Yellow Perch and Rainbow Trout) blue
tilapia can thrive a wider range of temperatures, this will drastically increase their chances of surviving if
there is a sudden temperature flux within the system.

The following table compares three vital characteristics for the rearing of fish: Temperature, Ammonia
Tolerance and pH range. Blue tilapia is superior in both the temperature range and the ammonia
tolerance. Ammonia Tolerance is the highest level of ammonia in the water supply that a fish can live in
without becoming toxic to consume. The team therefore decided that Blue tilapia was the ideal fish for
the system.

Fish Species Temperature Range

*C

Maximum Ammonia Tolerance Level

mg/L

pH Range

Blue Tilapia 8.0- 42 7.1 3.7- 11
Yellow Perch 10.0- 37 7 2.6- 10
Rainbow Trout 0.0 – 22 6.7 3.7- 11
(Mjoun, 2010)
Table 13. Comparison of different Fish Species