Bacterial flora associated with a trophic chain consisting of microalgae, rotifers and turbot larvae: Influence of bacteria on larval survival

Abstract

In order to increase knowledge about the bacteria in cultures and their influence on the culture performance, bacterial analyses and physical and chemical measures were carried out for different biotopes of two similar trophic chains (A and B). These trophic chains consisted of microalgae ( Pavlova lutheri or Platymonas suecica), rotifers ( Brachionus plicatilis) and turbot larvae ( Scophthalmus maximus). About 10 7 bacteria/ml were regularly observed by direct counts in the culture water of the algae and rotifers, and from 10 4 to 10 5 bacteria/individual in rotifers and turbot larvae. In general, the composition of the bacterial flora presented some elements of stability, since some taxa were found in successive samples of the same biotope. On the other hand, there were very few similarities between the bacterial flora of different biotopes, except between the gut of the rotifers and their medium. Nevertheless, among the Vibrionaceae, which were the chief constituent of the bacterial flora in the gut of the turbot larvae, some were probably introduced by the rotifers. The numbers of Vibrionaceae in both rotifer cultures increased over the course of the experiments. The turbot larvae B refused to ingest prey which contained large quantities of bacteria and died on days 7 and 8, whereas 40–60% of larvae A remained alive at day 10. The conclusions drawn from this experiment can be applied to improving the survival and growth of larvae as well as to developing sanitary procedures for hatcheries.