Advancement of rotifer culture and manipulation techniques in Europe

Since no artificial feed formulation for first feeding of marine larval fis h has been developed yet, live prey feeding remains essential in commercial marine hatchery operations. Because cultured rotifers are relatively poor in eicosapentaenoic acid (EPA: 20:5n-3) and docosahexaenoic acid (DHA: 22:6 n-3), it is essential and therefore common practice to enrich these live pr ey with emulsions of marine oils. The short-term exposure to oil emulsions results in lipid-encapsulated rotifers with high EPA and DHA levels. Howeve r, these rotifers are prone to fast losses of their gut content and show a distortion in their protein/lipid balance. Rather than submerging rotifers in oil emulsions, it is often preferred to use formulated culture diets whe n medium to low enrichment values are needed in live prey. The use of these diets contributes not only to the filling of the gut of the rotifers with nutrients, it generally creates a more stable entire body composition which is important especially when rotifers are not consumed immediately by the larvae. New culture techniques for rotifers, such as closed recirculation systems, are offering new possibilities for continuous supplies of high quality roti fers at 10 times higher densities than in batch cultures. The production in crease in these systems is explained by the better water quality obtained b y the introduction of protein skimmers. ozone treatment, and biological fil tration. Although disinfection of rotifers remains a bottleneck, it has bee n observed that rotifer populations cultured at high densities are not pron e to higher bacterial infestation. Also, the problem of unexplained mortali ties in batch cultures seems to be partly solved by the introduction of rec irculation systems or by bacterial management (introduction of probionts). which allow more reliable rotifer production. (C) 2001 Elsevier Science B.V . All rights reserved.