Prebiotics in Finfish: An Update - Aquaculture Nutrition: Gut Health, Probiotics and Prebiotics - page 393

all the genes were up-regulated compared with the control group. Surprisingly, the challenge
experiment with P . damselae subsp. piscicida (IP) revealed that cumulative mortality of fish
fed synbiotic was significant higher than that in the control group. The study of Cerezuela etal .
(2013a), investigating the effect on intestinal morphology and allochthonous intestinal micro-
biota, revealed signs of damage in the anterior intestine similar to that reported in fish fed inulin
(Olsen et al . 2001). Synbiotic administration significantly increased villi height and intestinal
diameter, but reduced the number of goblet cells and microvilli height, compared to control
fed fish. Intestinal microbiota evaluation by DGGE revealed that number of OTUs in fish fed
synbiotic was significantly lower (6.0 ± 0.0) than the number (17.3 ± 0.9) detected in control
fed fish. Cerezuela et al . (2013b) investigated the effect of synbiotic administration on intesti-
nal gene expression in gilthead sea bream, and revealed that only β-actin and occludin were
significantly affected by synbiotic supplementation, although the expressions of nearly all the
genes were up-regulated compared with the control group. The conclusions of these studies
are that the synbiotic application of B . subtilis and inulin increases some immune parame-
ters, had a negative effect on gut morphology and gut microbiota, had less effect on intestinal
gene expression in anterior intestine and had a negative effect on disease resistance towards P .
damselae subsp. piscicida . Further investigations are warranted to ascertain if benefits can be
achieved with optimized inclusion levels.
14.13 CONCLUDING REMARKS AND FURTHER
PERSPECTIVES
Prebiotic administration in aquafeeds and their positive effects are becoming increasingly doc-
umented (Burr etal . 2005; Gatlin III etal . 2006; Denev etal . 2009; Yousefian and Amiri 2009;
Ganguly et al . 2010; Merrifield et al . 2010; Ringø et al . 2010; Sweetman et al . 2010; Dim-
itroglou et al . 2011a; Gatlin III and Peredo 2012). However, the influence on the intestinal
microbial communities (abundance, diversity and richness) and the ability of the intestinal
microbiota to ferment selected prebiotics is in its infancy. The fermentability of a prebiotic is
a key factor which influences its effects on fish growth performance, intestinal physiology and
health, which is at least partially related to its degree of polymerization (DP). Thus, fermen-
tation of prebiotics with various DPs should be investigated in in vitro and ex vivo studies in
future. These types of studies will help to elucidate suitable prebiotics, and optimum levels
of inclusion, for each different species dependent on our increasing knowledge of beneficial
endogenous intestinal microbial communities. Promoting beneficial intestinal bacteria species
with the use of prebiotics is a promising method for improving the overall condition of all ani-
mals. Altering the intestinal microbiota in favour of the beneficial bacteria may increase the
production of beneficial metabolic products and at the same time may reduce the production
of toxins. Hence, as has been reported in numerous studies, improved intestinal morphology is
promoted which can lead to elevated nutrient absorption and increased growth performance.
Even though several comprehensive reviews have been published (most recently, Torrecil-
las et al . 2014), currently there are gaps in existing knowledge on prebiotic applications to fish
and shellfish including various aspects of digestion, absorption, digestive enzymes, carcass
composition, metabolism, and influences on physiological responses, especially expression
of immunological genes, localized and systemic immunoglobulin production, gut morphol-
ogy, gut microbiota and disease resistance in challenge studies. Additional information is