D.5.1 | Rotifer Production: Liquid Microalgal Feeds

Net Biomass Conversion

(feed productivity and waste production)

Net biomass conversion is the rate at which feed biomass is converted into rotifer biomass and is excellent measure of the quality of a feed. The higher the net biomass conversion, the closer the feed matches the metabolic needs of the rotifer, making the rotifer culture healthier.

With higher net biomass conversion, less feed is used and significantly less “waste” is produced, to be consumed by protozoans and bacteria. Increasing net biomass conversion can increase production, rotifer and fish health, reduce fouling, and reduce labor cost.

Table D.2


Notes on Biomass Conversion:

  1. We measure productivity in terms of grams biomass of rotifers produced per gram biomass of feed added. We find that conversion rates are consistent across all methods of production. A continuous production system with a 25% harvest rate will have the same net biomass output per liter of feed as a continuous production system at a 45% harvest rate using the same feeds, and the same net biomass output as a batch system at 70% growth per day. Thus net biomass conversion is a very useful tool for comparing the productivity of feeds.
  2. The numbers above are average feed conversion rates from 2 years of testing at RMI. Not all rotifers will respond to the feeds in the same way all the time. Our cultures sometimes experience minor (10%) swings in productivity for a few weeks at a time. Some of our customers have reported better total productivity from RotiGrow Plus than from Nanno 3600, even though our numbers show the contrary. As with all of aquaculture, results will vary with conditions. Choose the microalgal feed that works best for you.

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