F.4.0 | Protocols and Tables (Enrichment) : Feed Calculation

Calculating Enrichment Feeds

Enrichment feed is calculated by the wet weight of the rotifer harvested and enriched, not by rotifer count, as rotifer vary considerably in size.

Screening the harvested rotifers prior to enrichment is not a recommended practice as it causes excessive rotifer stress. The preferred methods of determining wet weight are:

  • Sample a portion of the culture to be harvested,
  • Estimating wet rotifer weight from rotifer count using past experience or
  • Estimated wet weight from rotifer count and the rotifer length to weight converter (Table F.2).

Table F.2: Lorica Length to Mass converter


Once you know the wet weight of the rotifers to be harvested, feed the following amounts of N-Rich every hour (depending on the protocol you choose). Please keep in mind the enrichment points listed below in the feeding table.

Table F.3: Enrichment Feeding Rates


  1. Rotifers can be enriched at relatively high densities (4g wet weight per liter or 3000+ RMI “Mini-L160” rotifers per ml). N-Rich is a very clean feed and rotifers can be enriched at even higher densities, but Dissolved oxygen and ammonia stress can become an issue.
  2. The enrichment culture will be extremely clean. Nonetheless, it is helpful to use a fully equipped culture tank with aeration and filter floss for enrichment.
  3. Oxygen stress can severely compromise rotifers during enrichment. For Maximum rotifer health and delivery of nutrition to your larval fish, please monitor oxygen effectively.
  4. The greater the density of the enrichment culture the greater the demand for oxygen. Watch oxygen closely until you have a proven protocol. Please note that aeration can drive oxygen and impact the effectiveness of oxygen delivery. Changes in the size of the oxygen bubble can also significantly affect oxygenation.
  5. The enrichment culture will need increasing levels of oxygen after the first hour.
  6. Ammonia may be an issue with enrichments lasting more than 1 or 2 hours. If ammonia exceeds 5.0ppm ionized ammonia becomes toxic even if lowered pH prevents un-ionized ammonia from being toxic. It is helpful to add ClorAmX to keep Ammonia from becoming a problem.

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