Sammendrag
Production of juveniles is like triple jump, with production of high quality viable larvae, providing high quality food, and providing a g ood environment as the three steps. Success can only be achieved by m astering every step of the process. In spite of considerable progress during the last years, a �dark horse� seems to ravage both under pro duction and experimental situations. The symptom is generally the sam e: poor reproducibility in growth, survival and quality within replic ates. The problem is even manifested in full sibling groups, which in dicate that quality of larvae or nutrition is not the principal cause of the problem. An increasing number of experiments and observations point to bacteria as the main factor for the observed problems, but normally without identification of known pathogens. An ecological an alysis of todays rearing technology and practise indicate a selection for opportunistic bacteria in the hatcheries. Under such conditions the development of the bacterial communities is too much of a stochas tic process, and lack of reproducibility will be a key characteristic . The dominance of opportunistic bacteria at fairly high densities is most likely too much of a challenge for larvae that also experience other types of stress and have a poorly developed immune system. As a result our well known problems are manifested. A strategy to cope wi th the microbiological problems is proposed, which consist of three e lements: non-selective reduction of bacteria, selective enhancement o f beneficial bacteria, and improvement of the ability of larvae to su stain the bacteria in the environment. Various methods for the differ ent elements in the strategy are proposed, and experimental data demo nstrating the potential of the methods is presented.
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