Leit að bætibakteríum / Searching for putative probionts in the production system of halibut larvae




Jónína Þ. Jóhannsdóttir, Eyrún Gígja Káradóttir (MS student), María Pétursdóttir, Jennifer Coe, Heiðdís Smáradóttir, Rannveig Björnsdóttir

Supported by:

Tækniþróunarsjóður Rannís (2006-2008) / Technology Development Fund of Rannís, the Icelandic Center for Research (2006-2008)

Leit að bætibakteríum / Searching for putative probionts in the production system of halibut larvae

The overall goal of the project is to improve the survival and quality of halibut larvae in starter feeding using supplementary bacteria. In the composition of supplementary bacteria for fish, the breeding of warm-water species has often been considered, and the bacterial species that have been used have proved to have a poor foothold in the environmental conditions involved in the breeding of cold-water species, such as halibut. This project seeks out and identifies bacteria that are prevalent in halibut larvae from breeding units that have been successful in terms of larval performance and metamorphosis. Studies were performed on the properties of isolated bacterial strains in terms of growth inhibitory effects on known pathogens for fish as well as predominant bacterial species from halibut larvae in breeding units where the performance and quality of larvae were below average. The predominant bacteria were isolated from larvae in all breeding units of Fiskey hf. in two different periods in addition to which samples were taken from juveniles in export size. The results of studies on the growth inhibitory effect of isolated strains revealed 18 bacterial strains that were found to inhibit the growth of known pathogens and / or bacterial strains that had been isolated from the larval rearing environment. Sequencing results showed a good correlation with 6 different bacterial species. Subsequently, it will be treated with a selected mixture of additive bacteria in the early stages of halibut farming.

The overall aim of this project is to use probiotic bacteria to promote increased survival of halibut larvae during first feeding. Previous studies indicated that the microbial load of larvae and their environment represents a problem and the objective of this project was to search for possible candidates for probiotic bacteria to promote survival and growth of larvae use during the first and most sensitive phase of production. Potential probiotic strains were selected on the basis of dominance in the gut of larvae from production units with successful growth, development and survival. The growth inhibiting activity was tested against known fish pathogens as well as bacteria dominating the intestinal community of larvae from production units with poor overall success. We isolated dominating bacteria in the gut of larvae from all production units of two different spawning groups at Fiskey Ltd. and also from export-size fingerlings. Growth inhibition studies revealed 18 bacterial isolates that inhibited growth of known fish pathogens and / or dominating bacterial isolates from the gut of larvae of an overall poor quality. 16S rRNA sequencing revealed a reasonable correlation to 6 bacterial species and presently. As a next step, halibut eggs and larvae will be treated with selected strains to test their potential as probionts during the first production stages of halibut aquaculture.

View report