E. Lubzens, O. Gibosn, M. Khayat
Abstract:
The increased need for different size rotifers as food for raising small mouthed marine fish larval, led to the culture of different body size rotifers in mariculture facilities. While the culture of the relatively large Brachionus plicatilis can be performed at a wide range of temperatures (15-30 C), dependable cultures of the small size B. rotundiformis are obtained at relatively high temperatures 25-38 C). Recently, attempts are directed towards the culture of cold water marine fish that produce extremely small sized larvae. These larvae require small sized prey organisms during the first period after hatching from eggs. The introduction of small B. rotundiformis into these fish larvae culture systems has met with great difficulties, due to their sensitivity to low temperatures.
In the present study we addressed the following questions: 1. Is the survival of rotifers at low temperatures dependent on the accumulation of lipids and/or highly unsaturated fatty acids? Is it dependent on the synthesis of a specific shock protein?
Previous work showed that relatively large amounts of lipids, including highly unsaturated fatty acids accumulate in B. plicatilis kept at 10 C for at least 24 h. In addition, the B. plicatilis synthesized a approx. 90 kDa protein, that was not found in rotifers kept at 25 or 33 C. Higher amounts of total fatty acids were found in B. rotundiformis kept at 15 C for 48 h than those maintained at 10 C and both groups show substantial amounts of HUFA. While the amount of lipids per rotifer was lower in B. rotundiformis, this corresponded to their smaller size. However, these rotifers did not survive at lower temperatures, although several gradual exposure regimes were tested. In another series of experiments we found that B. plicatilis that were exposed to 33 C and 37 C and did not accumulate lipids or HUFA, survived at lower temperatures. Thus, the present results indicate that while lipids and HUFA accumulate in rotifers exposed to low temperatures, it may have resulted from their lower reproductive rates at these temperatures that also lead to accumulation of lipids and HUFA. Nevertheless, this lipid accumulation does not assure their survival at low temperatures.
The possibility that the approx. 90 kDa protein serves as a cold shock is currently investigated.
(National Institute of Oceanography, Israel Oceanographic and Limnological Research, Haifa, Israel)
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