A TALE ON OYSTERS, HATCHERIES, PATHOGENS AND PROBIOTICS
Juan L. BARJA and Susana Prado
Facultad de Biología-Instituto de Acuicultura. Universidade de Santiago de Compostela. 15782 Santiago de Compostela (A Coruña). España.
Key words: Ostrea edulis, European oyster, hatchery, pathogen, Vibrio
The presence of the European flat oyster Ostrea edulis in Galicia (NW Spain) is documented 2000 years ago. The Celtic inhabitants seemed to consume a variety of molluscs, as suggested by the accumulations of shells in their settlements. The Romans sent oysters to the metropolis in the first century.
In the XX century, oysters were yet used in Galicia as supplement for the agriculture, providing calcium and organic matter. Unfortunately, since 50’s the overexploitation of the natural beds and the appearance of diseases (as bonamiasis in 80’s) caused a deprivation of this valuable asset.
The decline of natural beds (and natural recruitment) has led to the need of hatchery production of seed to sustain the aquaculture of this species and to restore the original populations, avoiding the massive and uncontrolled importations. However, these installations are threatened by frequent episodes of larval and post-larval mortalities, which compromise the production and economic viability. The aetiological agents of these episodes have been identified mainly as bacteria belonging to genus Vibrio. These pathogens are not host-specific, affecting all the cultured bivalve species worldwide. The attempts to control the vibriosis by the preventive use of antibiotic have resulted ineffective, leading to the undesirable rise of antibiotic-resistances. In addition, the particular reproductive cycle of the flat oyster, protandric hermaphrodite with internal fertilization in the palleal cavity and larval incubation of 8-10 days before release, should be considered.
Innovative procedures are necessary to solve this problem, applying the new knowledge about the microbiological processes in the hatchery, considered as a whole with different interrelated compartments. Thus, improved protocols should be designed to verify the microbiological quality of seawater and microalgal cultures used as food. The management practices have to be updated on the basis of current scientific advances. And new approaches, as the use of marine bacteria with probiotic or quorum quenching activity, need to be adapted to the particular characteristics of bivalve hatcheries and specifically to the flat oyster culture.
The application of scientific knowledge to the improvement of seed production in hatcheries is essential to make the flat oyster aquaculture a sustainable and profitable activity.