New Strategies for the Control of Bacterial Infections in Marine Fish Larval Rearing - Aquaculture Microbiology and Biotechnology - page 8

colonizing the eggs or larvae may prevent the further colonization of
opportunistic bacteria originating from the diet (Hansen and Olafsen,
1999; Olafsen, 2001; Carnevali et al., 2004). Another advantage is that, in
contrast to adults, there is no acidic stomach barrier in most marine fi sh
larvae, and potential probiotics would not need to resist acidity (Tanaka et
al., 1996; Ronnestad et al., 2000).
Probiotics in marine larviculture have been recently reviewed by
Vine et al. (2006). The study of probiotics in fi sh larvae, summarized in
Table 1.1, has usually focussed on the use of commercially available or
selected terrestrial lactic acid bacteria (Gatesoupe, 1991, 1994; Planas et al.,
2004; Villamil et al., 2003; Carnevalli et al., 2004; Plante et al., 2007; Arndt
and Wagner, 2007; Benetti et al., 2008a, b; Suzer et al., 2008; Abelli et al.,
2009). Commercial yeasts have also been proposed as probiotics (Tovar-
Ramirez et al., 2002, 2004).
A better strategy, that avoids the introduction of non-native
microorganisms to the system, is to select probiotic candidates among
strains isolated from healthy fi sh (Ottesen and Olafsen 2000; Olsson et al.,
1992; Westerdahl et al., 1991; Meuer et al., 2006) or hatchery facilities (Huys
et al., 2001; Hjelm et al., 2004a, b). The effi cacy of autochthonous probiotics
is likely to be highest in the host species the bacteria were isolated from
(Verschuere et al., 2000).
Generally, selection is based on the antagonistic effect of the potential
probiotic against pathogenic bacteria responsible for high mortalities in
larvae, such as Vibrio anguillarum (Olsson et al., 1992; Planas et al., 2006),
Vibrio sp. (Gatesoupe, 1994; Vine et al., 2004a, b) or Aeromonas sp. (Ringø
and Vadstein, 1998; Vine et al., 2004a, b), but in vitro growth and adhesion
to mucus, immunostimulation or enhancement of enzymatic activity have
been also used as criteria for probiotic selection (Gatesoupe 1994; Suzer et
al., 2008; Picchetti et al., 2009; Vine et al., 2004a, b). It is important to note
that probiotics can be added directly to water or introduced to the system,
previously bioencapsulated in live prey ( Table 1.2 ) . In some cases, the fi nal
effect may depend on the selected way of delivery.
Synbiotics
A synbiotic is defi ned as a combination of a probiotic with a prebiotic,
usually a selective substrate, which ensures the growth and the permanence
of the associated probiotic (Ziemer and Gibson, 1998). In aquaculture,
the utility of synbiotics has been proposed by Vine et al. (2006) but at
the present moment only in vitro trials have been conducted to assay the
potential of non-digestible carbohydrates and other prebiotics on the
growth of probiotics (Rurangwa et al., 2009).