Follow-up of hatchery rotifer cultures with regard to their genetic identity SPIROS PAPAKOSTAS1, TANIA De WOLF2, ALEXANDER TRIANTAFYLLIDIS1, KALLIOPI VASILEIADOU1, DIMITRIOS KANELLIS1, PATRIZIA CECCONI2, ILIAS KAPPAS1 and THEODORE J. ABATZOPOULOS1 1. Department of Genetics, Development & Molecular Biology, School of Biology, Aristotle University of Thessaloniki, 541 24 Greece 2. Maricoltura di Rosignano Solvay srl, Via P. Gigli, Loc Lillatro, I-57013 Rosignano Solvay, Livorno, Italy Abstract Brachionus sp. rotifers are widely used in large numbers for larval rearing in fish industry. By practice, cultured rotifers are discriminated on the basis of their body size. Recently however, marked polymorphism has been uncovered with the use of molecular markers. Rotifers of the same size but of distinct genetic profiles have been shown to differ in environmental preferences. Thus, mass culturing practices in hatcheries should be re-considered. In this study, we have followed a number of experimental cultures from an Italian hatchery. The genetic composition of the cultures was recorded and it was revealed that a single Brachionus biotype was prevalent in all cultures. Results indicate that the few observed crashes occurred soon after upscaling. Diet change seems to be a possible factor leading to this outcome. In a single occasion, contamination was observed but the co-existence of different Brachionus types did not affect culture performance. In the future, detailed joint analyses of the genetic identity and culture preferences of the different Brachionus rotifers will provide useful insights into performance-related problems in hatcheries.   < back .