OK. Here we are again to discuss fish food. Yay!
When we left off last week we had finished a quick primer on Proximate Composition Analysis. We discussed how a feed sample can be broken down to its constituent parts namely Moisture, Crude Protein, Crude Lipids, Crude Fiber, Ash and NFE. It is also important to consider the amount of energy stored in the feed. After all, that is the point of eating, right? Unfortunately, some of the energy is indigestible and not available to the fish.
This is essential to the understanding of how to create a feed that meets the recipients needs. In an earlier post we reported on the general needs of Tilapia as determined by the published contents of commercial feeds. Of course, we are assuming that the feed company has properly done their homework. To verify and confirm their results would require extensive studies regarding feed conversion but this could be done if one desired to do it.
We also stated that we expect to have access to several species to be used as feed stuffs. These included Eisenia foetida (Red Wiggler worms), Hermetia illucens (BSFL), Lemna minor (Duckweed), and Azolla caroliniana (Azolla). Researching the literature for Proximate Composition results for these species leads to a plethora of information. Many, many studies have been done in an effort to evaluate the suitability of these insects and simple plants as food stuffs for everything from fish to poultry to swine, and yes, even for human consumption!
In the end we selected results to use in our work which we felt were somewhat representative of the range of reports.
Eisenia foetida, (Mengist, 2016)
Lemna minor, (Khandaker et al., 2007)
Hermetia illucens, (Pieterse, 2014)
Azolla caroliniana, (Sujatha et al., 2012)
We used %DM in all of our ensuing work which mainly consisted of setting up and solving a system of simultaneous equations for achieving a desired goal of nutrient concentrations in the final mixture.
The energy value may be estimated (in kcal/g) by multiplying the percentages of crude protein, crude lipid, and carbohydrate (NFE) with the recommended factors (2.44, 8.37, and 3.57 respectively) as proposed by Martin and Coolidge (1978).
So, how many pounds of candy with 30% sugar must be mixed with 4 pounds of candy with 70% sugar to make candy with 43% sugar? We all remember that type of nightmare simultaneous equations problem from high school algebra, right? LOL.
Actually, with matrices, it’s really not that difficult to solve these problems today. Here’s a link to the spreadsheet we created to solve these equations using matrices. It can be used to create 2, 3 or 4 ingredient foods of user settable target values given analyses of the food stuffs to be used. It comes with no warranty, guarantee, or even instructions. You’re on your own for now. Maybe we will try to explain it in a later post but I think you can work it out on your own.