Probiotic Applications in Temperate and Warm Water Fish Species - Aquaculture Nutrition: Gut Health, Probiotics and Prebiotics - page 265

induced mortalities in Senegalese sole during an in vivo challenge study. In this investigation
Senegalese sole, with an average weight of 15-20 g, received the feed supplemented with the
potential probiotic Pdp11 for 15 days while the control received a non-supplemented feed.
After the V. harveyi challenge experiment the mortality in fish receiving the diet supplemented
with Pdp11 (10%) was significantly lower than that in fish which received a normal diet with-
out the probiotic (60%). The relative percentage survival (RPS) for the challenge assay with
V. harveyi was 83.33%. The demonstrated ability of the bacterial strain to interfere with V.
harveyi adhesion to mucus, as well as the adhesion to host surfaces, were suggested to be par-
tial mechanisms in which Pdp11 reduced sole mortalities during the challenge. In addition, Sh.
putrefaciens (Pdp11) and Sh.baltica (Pdp13) have been reported to reduce mortalities in Sene-
galese sole after challenges with Photobacterium damselae subsp. piscicida (Díaz-Rosales
et al . 2009; de La Banda et al . 2010). In particular the results reported by Díaz-Rosales et al .
(2009) showed that despite their affiliation within the same genus, and the same origin of both
microorganisms assayed, their effects on mortality and respiratory burst activity were differ-
ent. In fact, the cumulative percentage of mortality after the Photobacterium damselae subsp.
piscicida challenge was 100% in the groups fed with the control diet, whereas mortality rates
observed in the groups fed with Pdp11 and Pdp13 supplemented diets ranged from 75% to
100% and 65% to 80%, respectively. In all cases the mortality of fish receiving the diet sup-
plemented with Pdp13 was significantly lower than in fish receiving the diet supplemented
with Pdp11; however, only Pdp11 significantly enhanced superoxide anion production by sole
HK phagocytes. The authors suggested that the increase of the respiratory burst activity of the
sole phagocytes could be strain dependent; however, this stimulatory effect was not essential
to enhance survival after the challenge with Photobacterium damselae subsp. piscicida , and
thus Pdp13 could exert its effects on immunological abilities differently from respiratory burst
activity. More recently de La Banda et al . (2012) further investigated the health protection
induced by the strain Pdp11 on Senegalese sole juveniles. In this study Pdp11, both fresh and
lyophilized cells, were incorporated into fish feed at a concentration of 10 9 cells g -1 , and then
given to juvenile sole for 2 months. At the end of the study, fish were challenged by intraperi-
toneal (IP) inoculation with Photobacterium damselae subsp. piscicida . In this case the RPS
obtained ranged between 25% and 44% for fish receiving both probiotic supplemented diets,
although only fresh Pdp11 enhanced Senegalese sole growth when compared with control.
Such positive effects of Shewanella species reported on Senegalese sole juveniles are in agree-
ment with previous data obtained on developing sole (Makridis et al . 2008) where early phase
larval survival was improved with the application of various bacteria, including Shewanella .
The authors set up the feeding experiment of sole larvae and post larvae comprising three treat-
ments: cultures of a Vibrio sp. (strain 2J18) were added to treatment A; a Gram-positive strain
J84 (unidentified Gram-positive, oxidase-negative and catalase-positive) and Shewanella sp.
(strain 2J27) were added to treatment B; and no bacteria were added to the control, treatment C.
The results evidenced that the addition of bacteria in treatment B increased survival of larvae
in the first phase of the experiment (0-20 dph) while no differences were observed in survival
during the second phase (20-60 dph). Although the current knowledge demonstrates that the
use of beneficial microbes at the larval stages can improve sole survival and disease resistance,
further studies are necessary to clarify if these benefits are due to microbial control by various
mechanisms, such as competition for nutrients, production of bacteriocins and competition for
attachment sites, and/or if they are due to immunomodulatory effects.