Monday, January 25, 2010


Motte Emmerik*, Delphine Serpin, Gaetan Shires, Paula Pinto, Yadir Mauri, Marlon Santana, Mayra Valdez, Jorge Medina, Efraim Cayra, Benoit Diringer, Segundo Cornejo, Eric Mialhe.

Marinazul/Conceptazul S.A, Guayaquil, Ecuador, PB 0902-142A
One of the main challenges facing a successful breeding of shrimps and fishes at larval stages corresponds to the colonization of the digestive tract by beneficial microorganisms which are able to trigger the right physiological development of the digestive tract itself, to reinforce the immune system, as well as to improve the digestive metabolism of the larvae. Indeed, the nature of such microbiota plays an important role in the protection of shrimp and fish against pathogenic and opportunistic bacteria. As a general rule, aquaculture production systems are disturbing the natural process of primary colonization of the digestive tract due to disinfection measures and a resulting low bacterial diversity in the water. In such conditions, the presence of pathogenic bacteria in the water or in live foods significantly increases the risks of animals infections due to the initial lack of native microbiota competitors present in the digestive tract.

In this respect, the domestication of the digestive tracts microbiota has become a priority for productivity improvement in shrimp and fish aquaculture. We have initiated research works in order to obtain a set of microorganisms which are constitutive of the native microbial flora of shrimp (Litopenaeus vannamei) and fish (tilapia Oreochromis niloticus and Green Terror Aequidens rivulatus). These microorganisms are set to colonize, in a monitorable and reproducible way, the digestive tract of laboratory larvae, according to a process known as conventionalization in gnotobiology science. Such conventionalized larva is expected to have a regular and superior physiology in comparison with the common hatchery-produced larvae.

In order to carry out this work, we have isolated, characterized and identified the constitutive flora of wild shrimps and fishes digestive tract at different life stages (larvae, juveniles and adults). The characterization work has been based on the application of metabolic tests, antagonisms tests and the use of molecular techniques for the analysis of gene sequences such as 16S rRNA, rpoB, 18S rRNA, ITS1, lactonase. These works have provided us with a large collection of gram (-) and gram (+) bacteria, some of which with probiotic potential.

The conventionalization process was realized through mono- and multi-specific ways in order to evaluate the gains in terms of larval growth and the resistance to challenge infections with pathogenic bacteria. As a preliminary step, we established protocols for egg and larva disinfection before inoculation of microbial strains. Then, the selected bacteria were administered directly through the culture water or by means of artemia encapsulation at the first days, before and after the opening of the mouth and the anus.

The results of the present work have shown that larvae inoculated with selected microbial combinations, gain in growth and survival in comparison with larvae maintained in aseptic conditions and inoculated with the set of bacteria associated with live and artificial foods. This study constitutes a preliminary approach, which must be optimized in order to assess the huge collection of available bacteria in experimental and production facilities.

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