Yes, you can eat the fish. But it takes 240 days to raise (feed) a tilapia to 1 lb of weight. There are cheaper and faster sources of protein. For example, soy beans take 45-100 days and yield .25lb of pods per plant.
Tilapia are protein producing machines. They convert 1.1-1.3 lbs of feed to 1 lbs of protein in 9 months (some factors like temperature, feed rate at different stages of life, and other things affect this ratio). But here's the real kicker--by providing the nitrogen that crops need, the crops can then turn CO2 into into calories via photosynthesis. Super high quality produce becomes the extremely valuable byproduct, effectively, of aquacultured seafood.
From a global net energy perspective, this is huge. Where do you think that nitrate fertilizer for soybeans is coming from? The Haber-Bosch process is crazy energy expensive. Growing soybeans for protein also has huge environmental costs--see deforestation in Brazil for details. 80% of cultivable land on earth is already in use, but food production needs to increase by 70% by 2050. Protein production will need to double due to the rising global middle class. And that middle class wants fish.
On top of all that, there's the fact that people don't want to eat just soybeans for protein. There's now more seafood consumed globally than beef cattle. By 2030, 62% of all seafood will be aquacultured, and there are some suggestions that most of the wild seafood species we know will be either extinct or heavily depleted.
Myself, and other conscious humans, conscious of the consciousness in animals, are concerned about quality of life (this is not the same thing as Veganism).
One example of a solution I deem unacceptable is raising rabbits for meat in stacked cages in an urban garage. (This has been advocated numerous times among various alternative food groups and I have read personal accounts of it's practice.)
How are 4^3 IBC tank 'cages' any different?
This has the potential to be the next theoretically-sterile factory farming failure, or a thriving, balanced ecosystem.
All very nicely illustrated by your work.
> They convert 1.1-1.3 lbs of feed to 1 lbs of protein in 9 months
They eat 1.1--1.3 lbs of food each month during 9 months, that is 9x1.1 -- 9x1.3 = 9.9 -- 11.7 lbs in total and produce 1 lbs of protein? Or the eat in total only 1.1--1.3 lb of food during the 9 months an produce 1 lbs of protein?
> But here's the real kicker--by providing the nitrogen that crops need
The fishes don't fixate nitrogen. They can "free" some nitrogen compounds in their food, but the nitrogen compounds have to come from somewhere. IIRC only some bacteria can fixate nitrogen naturally, (i.e. transform some unuseful nitrogen from the air into useful nitrogen compounds, that may be used to build proteins). Some plants, like soy, are good host for these bacteria, but I never heard that fishes have a similar symbiotic relation.
How are you planning to find suitable space / scale in such conditions?
Soy is probably more efficient, but soy is not fish and soy does not promote the healthy growth of other specialty crops like lettuce etc.
But, if you have a study that talks about the efficiency of nitrogen added directly versus the nitrogen that comes from the fish, or how it differs, I would be super curious to read it.