Rotifers remain the most widely‐used live feeds for early stages of larval fish culture, and success depends on hav‐ ing a stable supply of healthy rotifers that deliver the nutrition larvae need for rapid growth and normal development.
The nutritional value of rotifers de‐ pends 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 it 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 must then 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
Continuous enrichment using whole algae growth feeds during grow‐out so that the entire body of the rotifer is enriched is by far the most effective enrichment strategy.