Community Research and Development Information Service - CORDIS

Definition of specific protocols for colonisation of live prey organisms by potential probionts and their delivery to fish larvae

The cultivation conditions of live feed organisms as rotifers and Artemia favour growth of opportunistic microorganisms. Disinfection may reduce the bacterial load of the live feed, but the treatment is not necessarily successful as the level of organic nutrients for bacterial growth is not affected and opportunistic microorganisms proliferate within short time after treatment. A change, rather than a total decimation, of the bacterial flora of live feed should be aimed at. This should be done in a way that reduce loading of detrimental bacteria into the larval rearing tanks through the live feed and that introduce bacteria with probiotic properties.

To reduce the transfer of opportunistic bacteria from live feed cultures to the larvae, probiotic bacteria can be bioencapsulated by short term treatments of the cultures in suspensions, to exchange the flora of the live feed with the probiotics.

If probiotic bacteria are unable to establish themselves on the mucosal surfaces of the larvae or on the tank walls, they will have to be added regularly, either to the water or via the live feed. Addition to water is most effective at stagnant rearing conditions, as water exchange normally will have stronger impact on the number of the added bacteria, than the growth rate of the bacteria will. The flora of live feed can be exchanged by incubating the organisms in water added the probionts. Dense suspensions are necessary to induce effective exchange of the flora, and load the organisms with high numbers of the probionts within 30 minutes.

The probiotic bacteria may, however, have a short stability in rotifers and Artemia. As much as 90% of the probionts can be lost from the animals within one hour after bioencapsulation. When feeding with rotifers the loss may correspond to a load of >105CFU/ml to the water at each feeding. To reduce the total CFU of the organisms before they are fed to the larvae a decontamination step therefore should be included, and the project suggest that one hour decontamination in clean water reduce the bacterial content to normal or even lower levels.

The project has shown that there are differences between bacterial strains in how they are ingested by live prey and how stable they are. Administration of single or mixed strains have impact on the uptake by live feed, and on the colonisation of larvae.

Reported by

Instituto de Investigaciones Marinas, Eduardo Cabello 6
36208 Vigo
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