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Fish Silage: Turning Fish into Fertilizer

May 26, 2011

Island School students, Aldis, Brett, and Sara are doing a human ecology project that utilizes the cobia harvesting waste into livestock feed and fertilizer, trying to further close the loop in our sustainable model here at CEI/IS.  The fish silage will be used to feed the pigs and tilapia, as well as a fertilizer at the farm.

This was the first harvest of cobia in 2011. A total of 90 cobia were harvested, weighed, and hand filleted by Aldis, Brett, Sara, Luis, Matt, and Easton. The remaining cobia carcasses were ground up by hand using a meat grinder. The resulting slur was placed in a plastic drum, while Sara added muriatic acid Brett did the honors of stirring everything evenly, despite the fumes.

The silage was then left to break down into a protein soup, with plans to be used as fertilizer in our garden at The Island School.  This may seem fairly gruesome and sad to some, but not us! The harvesting-silage team was overly excited and kept happy with good company and good tunes- a little James Brown and Bob Marley!

3 Comments leave one →
  1. Justin permalink
    December 10, 2011 2:52 pm


    How is the use of the fish silage in feed for pigs going? What are the results? Any tainty smell in the meat? I’m interested in the results.


  2. Carls permalink
    April 27, 2012 9:48 am

    How do you know when the silage is optimus for its uses, i mean, how do you know when use the silage as a fertilizer, how much must be its hydrolisis degree??

    • April 28, 2012 8:48 am

      I determined the time needed to liquefy the silage based on the work of J.S. Goodard and O. Fagbenro and the procedures they established. By reducing the ensilage time to 3-7 days the total breakdown of the proteins in the fish carcasses is halted and better weight gain is achieved when fed to our tilapia. After 3 days of liquification we neutralize the silage using sodium bicarbonate and then co-dry by mixing with grains. This is further dehydrated in a solar oven to improve is storage time.
      -Josh Shultz (

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