Two episodes of mortality of cultured carpet shell clams (Ruditapes decussatus) associated with bacterial infections were recorded during 2001 and 2002 in a commercial hatchery located in Spain. Vibrio alginolyticus was isolated as the primary organism from moribund clam larvae that were obtained during the two separate events. Vibrio splendidus biovar II, in addition to V. alginolyticus, was isolated as a result of a mixed Vibrio infection from moribund clam larvae obtained from the second mortality event. The larval mortality rates for these events were 62 and 73%, respectively. Mortality was also detected in spat. To our knowledge, this is the fist time that these bacterial species have been associated with larval and juvenile carpet shell clam mortality. The bacterial strains were identified by morphological and biochemical techniques and also by PCR and sequencing of a conserved region of the 16S rRNA gene. In both cases bacteria isolated in pure culture were inoculated into spat of carpet shell clams by intravalvar injection and by immersion. The mortality was attributed to the inoculated strains, since the bacteria were obtained in pure culture from the soft tissues of experimentally infected clams. V. alginolyticus TA15 and V. splendidus biovar II strain TA2 caused similar histological lesions that affected mainly the mantle, the velum, and the connective tissue of infected organisms. The general enzymatic activity of both live cells and extracellular products (ECPs), as evaluated by the API ZYM system, revealed that whole bacterial cells showed greater enzymatic activity than ECPs and that the activity of most enzymes ceased after heat treatment (100°C for 10 min). Both strain TA15 and strain TA2 produced hydroxamate siderophores, although the activity was greater in strain TA15. ECPs from both bacterial species at high concentrations, as well as viable bacteria, caused significant reductions in hemocyte survival after 4 h of incubation, whereas no significant differences in viability were observed during incubation with heat-killed bacteria.Culture of carpet shell clams (Ruditapes decussatus) is a traditional activity that has great economical importance in Spain, particularly in Galicia (northwest region of Spain). Therefore, losses in production of this clam species would seriously affect the economy of this region.Globally, clam production is often affected by vibriosis, which leads to high mortality rates mainly in nursery cultures of juvenile bivalves (20,35). In Spain serious mass mortalities associated with Vibrio tapetis infections have been reported previously (15, 21). V. tapetis causes brown ring disease in Ruditapes species, which is characterized by the appearance of brown conchioline deposits that have variable distributions and variable thicknesses on the inner shell of diseased clams (41, 42).Susceptibility of other cultured bivalve species to infections caused by bacteria belonging to the genus Vibrio has been found in several scallop species, including Aequipecten irradians (52), Euvo...

In the present work, the effects of several lactic acid bacteria on the immune response of turbot (Scophthalmus maximus) macrophages have been studied both in vitro and in vivo. Out of six lactic acid bacterial strains tested, only heat-killed Lactococcus lactis significantly increased the turbot head kidney macrophage chemiluminescent (CL) response after 24 h of incubation. Nitric oxide (NO) was also significantly enhanced by this bacterium after 72 h of incubation with either viable (10 3 and 10 6 cells/ml) or heat-killed (10 6 cells/ml) bacteria. Viable Leuconostoc mesenteroides (10 6 cells/ml) was also capable of significantly increasing NO production. Since L. lactis proved to be the strain with more effects on the host immune function, further in vivo and in vitro experiments were conducted with this bacterium. The in vitro capacity of L. lactis to adhere to turbot intestinal mucus was positively confirmed. When orally administered, L. lactis significantly increased the macrophage CL response and the serum NO concentration after 7 days of daily administration. The antibacterial effect of the extracellular products from the six LAB strains against the fish-pathogenic bacterium Vibrio anguillarum was also demonstrated in vitro.The increased intensification of aquaculture has led to a high number of disease outbreaks with an increasing range of pathogens. Consequently, the extensive use of broad-spectrum antibiotics in aquaculture has led, as in other fields, to drug resistance problems (32). In order to improve health and welfare in the rearing of these animals, several alternatives such as improved husbandry, nutrition, and water quality; lower stocking densities; and use of vaccines, nonspecific immunostimulants (7), and bacterial probiotics such as lactic acid bacteria (LAB) (9, 26) have been proposed.Probiotics are defined as microbial dietary adjuvants that beneficially affect the host physiology by modulating mucosal and systemic immunity, as well as improving nutritional and microbial balance in the intestinal tract (23).The role of LAB within the digestive tract of endothermic animals and humans has been extensively studied (14,18,28), while only a few studies have demonstrated that LAB are part of the normal intestinal microflora in larvae and juvenile fish (25). Most studies with probiotics conducted to date with fish have been undertaken with strains isolated and selected from aquatic environments and cultured animals. The main bacteria tested belonged to the genera Bacillus, Vibrio, and Pseudomonas (9, 22). Few authors have tested in vivo the protection conferred by probiotics in fish experimentally infected with pathogens. Gastesoupe (8) found that the Lactobacillus or Carnobacterium strain isolated from rotifers increased the resistance of turbot larvae against a pathogenic Vibrio sp. Gildberg et al. (10) demonstrated that Carnobacterium divergens decreased the mortality rate of Atlantic cod fry challenged with Vibrio anguillarum but not the mortality of salmon fry challenged with Aeromonas hy...

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