PHYSIOLOGICAL ADAPTATIONS IN THE SURVIVAL OF ROTIFERS (BRACHIONUS-PLICATILIS, MULLER,O.F.) AT LOW-TEMPERATURES

The biology of the rotifer Brachionus plicatilis has been studied exte nsively in recent years, due to its importance in aquaculture. Today, the culture of several marine fish species relies completely on the da ily production of live rotifers. In the present paper we explore the c onditions that facilitate maintaining live rotifers for extensive peri ods at low temperatures. In addition to its possible contribution in p roviding reserve stocks for commercial application, these studies may be of ecological importance. They could explain some of the physiologi cal adaptive mechanisms that are involved in the survival of rotifers under adverse environmental conditions. Experimental results showed re latively high survival rates (82-85%) in rotifers that were cultured a t 25 degrees C and exposed later to -1 degrees C for 12-14 days. Durin g this period, rotifers were kept without food and their media were no t changed. The survival was found to depend on the rotifer culture con ditions, prior to exposure to -1 degrees C. These included the type of food fed to rotifers (yeast or algae), the salinity in which they wer e cultured, and an essential acclimation period of 2-6 day at 4 degree s C or 10 degrees C. The acclimation period was associated with the sy nthesis of at least one specific protein and accumulation of lipids. P rofiles of protein synthesis in rotifers incubated at 10 degrees C rev ealed a 94 kD protein, which did not appear in rotifers cultured at 25 or 37 degrees C. Immunoisolation, using a polyclonal antibody that wa s prepared against HSP60, revealed that this protein was synthesized i n rotifers kept at 10, 25 or 37 degrees C. However, this antibody did not react with the 94 kD peptide. In addition, rotifers kept at 10 deg rees C accumulated substantial amounts of lipids, including eicosapent aenoic acid (EPA), which is found in the algae fed to them. These resu lts support the hypothesis of specific adaptations to survival at low temperatures during an acclimation period.