The nutritional value of rotifers depends entirely on the feeds used to produce them. Typically, a batch culture is grown to harvest density using a low-cost, yeast-based feed of low nutritional value, and then is switched to a high lipid content “enrichment” feed a few hours before feeding to larvae. This “gut loading” strategy fills the digestive tracts of the rotifers with the lipid-rich feed, to be delivered to the larvae when the rotifers are consumed. But this conventional approach to enrichment is best described as “Too much, too late.”
Active, clean, healthy rotifers are essential for healthy larvae. Unfortunately, the extreme lipid content of conventional enrichment feeds is stressful to rotifers, weakening them and reducing their motility. Lipid emulsions foul the enrichment tank as well as the rotifers, so much of the enrichment feed is not consumed by the rotifers and is therefore wasted. The emulsion-fouled rotifers then must undergo stressful harvesting and washing procedures before being fed to larvae.
Rotifers that have been stressed by intensive enrichment and washing are invariably compromised. This stress is more evident when the popular “cold bank” technique is used (storing rotifers in a cooler and feeding over 18-24 hours). Temperature shock when enriched rotifers are cold banked often causes the rotifers to eject their gut contents (and enrichment), fouling the cold storage and further weakening or killing many of the rotifers before they are fed to larvae.
A new paradigm
A far more effective enrichment strategy is continuous culture grow-out enrichment using enriching, whole-algae growth-feeds so that the entire body of the rotifer is enriched. The benefits are multiple ... Read the full article from the Summer 2014 issue of the Hatcheryfeed magazine.
