Aquaponics critics rarely mention that you can often close much (though not all) of your production loop by feeding the waste products from the final produce back to the fish. And with tilapia (and to a lesser extent catfish), feed sources are trending in the direction of insect meal, which has a super efficient protein conversion rate.<p>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.<p>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.