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a molecular basis, using pH as a stressor and cortisol and 70 kDa heat shock protein (HSP70)
gene expression as indicators, Rollo
et al.
(2006) demonstrated that the addition of the pro-
biotics
Lb. fructivorans
and
Lb. plantarum
could also improve larval stress tolerance. These
results showed the importance of live feed supplementation with probiotics in early stages of
larval development.
In an interesting multiple application approach, Avella
et al.
(2010) tested a commercial
probiotic mixture (
Bacillus subtilis
,
Bacillus licheniformis
and
Bacillus pumilus
) delivered to
sea bream larvae via water exclusively or via both water (10
4
bacteria ml
-1
) and live prey
(rotifers and
Artemia
). The probiotic effect was assessed based on survival and on microbial,
morphometric and molecular analyses. The expression of the genes involved in muscle growth,
insulin-like growth factor I (IGFI - muscle and cartilage growth promoter), and myostatin
(MSTN - myoblast proliferation inhibitor), and in stress (HSP70 and gluconocoticoid receptor
(GR)) were quantified by real-time PCR. The mixture of probiotics increased growth (length,
weight, higher expression of IGFI and lower of MSTN) and improved fish welfare (lower
expression of HSP70 and GR). The probiotic effect was higher when the bacteria were deliv-
ered exclusively to live feed. The probiotic bioencapsulation reduced total presumptive
Vibrio
(cultures on TCBS) in
Artemia
but no significant differences were found in total heterotrophic
bacteria (cultures on TSAS) or in total presumptive
Vibrio
in the larval gut. However, the
presence of the introduced bacteria in larvae was not monitored specifically and bacteria com-
position of the gut of larvae and juveniles was not studied.
16.7 PREBIOTICS AND SYNBIOTICS IN LIVE FEED
Prebiotics are non-digestible dietary compounds which cause a beneficial effect on the host by
selecting growth or activating the metabolism of one or a limited number of health-promoting
bacteria (Gibson and Roberfroid 1995). The application of prebiotics in aquaculture has been
recently reviewed (Merrifield
et al.
2010; Dimitroglou
et al.
2011; Ringø
et al.
2010;
Chapter
14
), and includes the use of inulin, fructooligosaccharides (FOS), short-chain fructoo-
ligosaccharides (scFOS), mannanoligosaccharides (MOS), galactooligosaccharides (GOS),
xylooligosaccharides (XOS), arabinoxylooligosaccharides (AXOS) and isomaltooligosaccha-
rides (IMO). Prebiotics are usually included in dry diets, in the form of extruded dry pellets
with different diameters according to fish size, limiting their use to weaned larvae and adults.
To our knowledge, no studies have been published on the use of prebiotics to increase
live feed production or to modulate their microbial communities, or in controlling detrimental
bacteria development. Only a recent publication by Daniels
et al.
(2010) described the use
of prebiotics in the enrichment of live prey. Those authors used
Artemia
as a way of bioen-
capsulation and delivery of MOS (12 mg l
−1
), alone or jointly with a commercial probiotic
preparation (containing
Bacillus
spp., 100 mg l
−1
), to European lobster (
Homarus gammarus
L.) larvae. The study demonstrated the viability of prebiotic bioencapsulation in live feed
and the beneficial effect of MOS in the growth and survival of lobster larvae. The positive
effect was enhanced by the simultaneous use of the probiotic, although the statistical analysis
showed that the enhancement could be explained by the cumulative (additional) outcome and
not by a synbiotic (synergistic) effect of both treatments. Electron microscopy revealed sig-
nificant increases in intestinal microvilli length and density in lobster larvae and post-larvae
fed with MOS-supplemented
Artemia
. The addition of MOS did not have a significant effect
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