Pathways of bacterial contamination during egg incubation and larval rearing of turbot, Scophthalmus maximus

Overall microbial levels in the water system of a turbot farm were similar to those found in regular sea-water. At the end of an incubation period, however, the numbers of colony-forming units (CFU) in Artemiu cultures and turbot eg incubation jars were up to four orders of magnitude higher than sea-water level. Rinsing of the foot organisms (rotifers) prior to feeding them to turbot larvae, however, significantly reduced bacterial numbers, thus reducing the number of cross-contaminations. Several species of Aeromonas, Pseudomonas and Vibrio among others, were identified in the eggs and larvae, or in the water in which these were incubated. Scanning electron microscop shows that the surface of unfertilized turbot eggs is a breeding ground for bacteria; the removal of these eggs from incubation jars is therefore recommended. The epidermis of turbot larvae was virtually free ofmicroorganisms.