Microbial interference and potential control in culture of European eel (Anguilla anguilla) embryos and larvae

Recent experimental research applying hormonally induced maturation in European eel has resulted in production of viable eggs and yolk-sac larvae. However, present incubation and larval rearing conditions are suboptimal and few larvae survive until onset of first feeding. The aim of this work was to investigate if high mortality during egg incubation and larval culture resulted from microbial interference. By suppressing microbial coverage and activity on fertilised eel eggs using antibiotic and disinfection treatment, egg hatching success and larval longevity were significantly improved. A new approach based on scanning electron microscopy was developed to quantify microbial coverage of eggs. Measurements of microbial coverage in combination with growth curves of egg-associated bacteria indicated that microbial activity rather than physical coverage led to reduced hatch success. In addition, an inverse relationship between microbial coverage of eggs and larval survival indicated that attachment of micro-organisms on the egg surface during the last 24 h of incubation affected later larval survival. These results suggest that microbial control through application of egg surface disinfection in combination with microbial management will be fundamental for improved post-hatch larval survival.