aquaponics tilapiaI’ve been doing several radio interviews a week for the past few weeks to promote my new book, Aquaponic Gardening. Radio interviews are usually fun because they are essentially conversations with very personable people about my favorite subject! Most of the hosts have read the book and they generally ask thought-provoking questions, especially around the global impact and environmental benefits of aquaponics.

A question that consistently comes up is about my assertion in the book that fish are the most “efficient” source of living animal protein available to us. What do I mean by this? If you hypothetically consider a kernel of corn as a complete unit of food, then it takes far fewer kernels of corn to grow a pound of fish (1.5 lbs of feed for every pound of fish) than it does to grow a pound of cattle (8 – 10 lbs of feed for every pound of meat). We are increasingly more limited in how many units of food we can produce on our planet to feed our ever-growing population. The most direct, or efficient, use of these “units” would be to feed people with them. The next most efficient would be to use them in fish feed, and, in this scenario, the least most efficient is to feed them to cattle.

Why is this so? There are really two reasons why fish convert their feed into flesh so readily.

  1. Homeothermy-poikilothermy

    (from Wikipedia)

    As warm blooded creatures, or “endotherms”, most of the calories that mammals expend go into maintaining core body temperature. The harder we need to work to maintain our body temperature, the more calories we expend. Fish are cold-blooded creatures, or “ectotherms”, and their internal body temperature is completely reliant on the temperature of their external environment, e.g. the water in which they live. As the chart (Wikipedia) above shows, cold-blooded animals like lizards expend far less energy (joules) pound for pound than do warm blooded animals like mice, and they can live in a broader temperature range just by slowing down their metabolisms when the temperature is not optimized for their species (in this example, too cold).

  2. The second reason why fish are so efficient is because they float lazily in water all day. Think about how little energy you expended the last time you floated in a swimming pool. Unless you were playing Marco Polo with the kids, you probably used more energy on your walk to the pool than you spent in it. One of my favorite explanations of this came from the book “Just Food” by James McWilliams (p 155):

“The ability to float effortlessly negates the need to undertake such energy hogging endeavors as standing, walking and running. All these forms of mobility are internal energy sinks for terrestrial creatures, but not for fish. A fish is ecologically honed to translate the majority of its caloric intake into ample flesh that’s edible, usually tasty, rich in protein, and flush with heart-healthy oil. This streamlined translation, if responsibly managed and harnessed by humans, has the potential to improve the environment while generating more protein with fewer resources.”

So the next time you are standing in your grocery store considering a choice between meat and fish for dinner, send your gaze over to the produce aisle and imagine the eight to ten pounds of corn that probably went into that pound of hamburger. That’s a lot of corn.