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The effects of dietary administration of probiotic Pdp11, a bacterial probiotic strain from the Alteromonadaceae family, on growth and stress tolerance to high stocking density was analyzed in juvenile gilthead sea bream Sparus auratus . In the first trial, juvenile specimens were fed during 116 days with control feed or diets supplemented with Pdp11, and growth, serum immunological parameters as well as plasmatic, hepatic and muscular metabolic parameters were assessed. Growth performance improved in group receiving probiotic compared to control group. No differences were observed for the assessed immunological or metabolic parameters. In the second trial, specimens from both groups from the first experiment were submitted to the following conditions for 15 days: i) group fed with control food and either under low density (3 kg/m 3 ), or high density (30 kg/m 3 ) and ii) group fed with probiotic supplemented feed and either under low density, or high density. Our results indicated that administration of probiotic Pdp11 in the diet promoted growth and improved stress tolerance under high stocking density, suggesting its use will be beneficial for the aquaculture industry of this species.

This study aimed to evaluate the influence of dietary administration of two probiotic strains belonging to Shewanella genus (Pdp11 and Pdp13), on juvenile Senegalese sole (Solea senegalensis, Kaup 1858). Fish were fed three experimental diets for 2 months: two diets supplemented with 109 cfu g−1 feed of Pdp11 and Pdp13 probiotics and one control group. At the end of the experiment, samples were collected to determine muscle and liver body composition and to study digestive tract and liver histology. A challenge with Photobacterium damselae subsp. piscicida (ip) was performed. Results showed a protection for fish receiving probiotic supplemented diets (Relative Percentage Survival 27.5 ± 2.5% for Pdp11; 32.5 ± 2.5% for Pdp13) and a better growth for control and Pdp11 diets. Higher total protein in muscle were detected for fish fed the probiotic diets and significant differences in muscle and liver fatty acid profiles were observed for Pdp11 and Pdp13 compared to the control. Light microscopy images from sole specimens fed the Pdp11 diet showed scarce presence of lipid droplets inside of enterocytes and hepatocytes while greater numbers were found in fish fed the control and Pdp13 diets. Finally, the DGGE technique results suggest that the addition of the probiotic strains of Shewanella genus highly influenced the intestinal microbiota of Senegalese sole specimens, although this effect may depend on the probiotic strain assayed.

The effects of dietary administration of two probiotics, Shewanella putrefaciens Pdp11 and Shewanella baltica Pdp13, on growth, respiratory burst activity of phagocytes of Senegalese sole (Solea senegalensis), and survival of fish challenged with Photobacterium damselae subsp. piscicida have been studied. Fish were fed for 60 days with three different diets: one control, and two diets supplemented with 109 cfu g− 1of probiotics Pdp11 (Pdp11 diet) and Pdp13 (Pdp13 diet). Respiratory burst activity of phagocytes from fish fed with diet Pdp11 significantly increased after 60 days of feeding, whilst this significant increase was not detected in phagocytes from fish fed control and Pdp13 diets. On the other hand, the cumulative percentage of mortality after the challenges with P. damselae subsp. piscicida, was 100% in the groups fed with control diet, whereas mortality rates observed in the groups fed with diets supplemented with Pdp11 and Pdp13 ranged from 75–100% and 65–80%, respectively. These results suggest that an increased respiratory burst activity of the phagocytes is not essential to increase the protection against the P. damselae subsp. piscicida. On the other hand, the use of both probiotics improved the growth, and the survival against the pathogen, in comparison with those fish receiving the control diet.

A bacteriological study of 25 outbreaks affecting cultured gilthead sea bream (Sparus aurata L.) in southwestern Spain from 1997 to 2000 has been carried out. Each year, the highest number of outbreaks occurred during winter and affected fish with sizes ranging between 2 and 25 g. The most frequently isolated microorganisms were identified as Vibrio (69.90%). Other microorganisms belonging to Pseudomonas spp., Photobacterium damselae ssp. piscicida, Cytophaga/Flexibacterlike and Aeromonas spp. were isolated with a frequency lower than 10%. The outbreaks with the highest mortalities of cultured gilthead sea bream were due to P. damselae ssp. piscicida. An increase in the number of resistances to different antimicrobials has been observed in this study with respect to previous studies carried out in the same area. This increase was very high in the case of some species of Vibrio, Pseudomonas spp. and P. damselae ssp. piscicida. D 2003 Elsevier Science B.V. All rights reserved.