MICROBIOLOGY AND MOLECULAR BIOLOGY REVIEWS, 1092-2172/00/$04.00+0 Dec. 2000, p. 655–671 Vol. 64, No. 4 Copyright © 2000, American Society for Microbiology. All Rights Reserved. Probiotic Bacteria as Biological Control Agents in Aquaculture LAURENT VERSCHUERE, 1 GEERT ROMBAUT, 1 PATRICK SORGELOOS, 2 AND WILLY VERSTRAETE 1 * Laboratory of Microbial Ecology and Technology, Department of Biochemical and Microbiological Technology, 1 and Laboratory of Aquaculture and Artemia Reference Center, Department of Animal Production, 2 Ghent University, 9000 Ghent, Belgium INTRODUCTION .......................................................................................................................................................656 DEFINITION OF PROBIOTICS..............................................................................................................................656 FUNDAMENTAL QUESTION: IS IT POSSIBLE TO MANIPULATE MICROBIAL COMMUNITIES? ....657 RECENT FINDINGS .................................................................................................................................................659 General Considerations .........................................................................................................................................659 Fish Eggs and Larvae.............................................................................................................................................660 Fish Juveniles and Adults......................................................................................................................................660 Crustaceans .............................................................................................................................................................661 Penaeid shrimps..................................................................................................................................................661 Crabs ....................................................................................................................................................................661 Bivalve Mollusks .....................................................................................................................................................661 Live Food..................................................................................................................................................................661 Unicellular algae .................................................................................................................................................661 Rotifers .................................................................................................................................................................662 Artemia .................................................................................................................................................................662 Microbially Matured Water...................................................................................................................................662 Interaction with Nutritional Effects .....................................................................................................................662 POSSIBLE MODES OF ACTION ...........................................................................................................................662 Production of Inhibitory Compounds ..................................................................................................................663 General aspects ...................................................................................................................................................663 Production in aquaculture .................................................................................................................................663 Competition for Chemicals or Available Energy ................................................................................................663 General aspects ...................................................................................................................................................663 Competition for iron...........................................................................................................................................664 Competition for Adhesion Sites ............................................................................................................................664 Enhancement of the Immune Response ..............................................................................................................664 Improvement of Water Quality .............................................................................................................................665 Interaction with Phytoplankton ............................................................................................................................665 RATIONALE FOR SELECTING AND DEVELOPING PROBIOTICS IN AQUACULTURE ........................665 Acquisition of Background Information ..............................................................................................................665 Acquisition of Putative Probiotics ........................................................................................................................665 Screening and Preselection of Putative Probiotics.............................................................................................666 In vitro antagonism tests ...................................................................................................................................666 Colonization and adhesion ................................................................................................................................667 Small-scale tests, with particular attention to monoxenic cultures ............................................................667 (i) Small-scale tests (xenic) ...........................................................................................................................667 (ii) Monoxenic cultures ..................................................................................................................................667 Evaluation of Pathogenicity of Selected Strains.................................................................................................667 In Vivo Evaluation of Potential Probiotic Effects on the Host.........................................................................667 Mode of application of the putative probiotic ................................................................................................667 Experimental infections—in vivo antagonism tests .......................................................................................668 Mass Production, Economic Evaluation, and Evaluation of Compliance with legislation ..........................668 Development of Monitoring Tools ........................................................................................................................668 CONCLUSIONS AND FURTHER DIRECTIONS.................................................................................................668 REFERENCES ............................................................................................................................................................669 * Corresponding author. Mailing address: Laboratory of Microbial Ecology and Technology, Department Biochemical and Microbiolog- ical Technology, Ghent University, Coupure Links 653, 9000 Ghent, Belgium. Phone: 32-09-264.59.76. Fax: 32-09-264.62.48. E-mail: willy .verstraete@rug.ac.be. 655