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associated microbiota (Qi
et al.
2009). Rotifers grown on baker's yeast show 10
3
-10
4
bacteria
per rotifer (Skjermo and Vadstein 1993; Pintado
etal.
2010), while the values for rotifers grown
on microalgae are generally lower, around 10
2
CFU rotifer
−1
(Øie
et al.
1994). Culturable
bacteria in rotifers fed with baker's yeast with added capelin oil were reported to be domi-
nated by members of the
Pseudomonas/Alcaligenes
group,
Cytophaga/Flavobacterium
group,
Alteromonas
and
Vibrio
genera (Skjermo and Vadstein 1993). Nicolas
et al.
(1989) observed
that the bacteria associated with rotifer cultures, identified by biochemical assays, were mainly
Pseudomonas
,
Vibrio
and
Aeromonas
, and to a lesser extent
Alteromonas
and
Acinetobacter
.
By denaturing gradient gel electrophoresis (DGGE) analysis, Rombaut
et al.
(2001) demon-
strated that bacteria in the culture water of rotifers were different depending on the culture
mode (batch or continuous culture). In recirculation systems, γ-Proteobacteria were predomi-
nant in the water, revealing the presence of species belonging to the genera
Marinomonas
and
Pseudoalteromonas
. However, the bacterial communities of rotifers were not analysed. In a
two-year survey, using both culture-dependent methods and DGGE, McIntosh
et al.
(2008)
observed a stable gut microbiota of rotifers grown on commercial diets, with predominance
of putative
Arcobacter
spp., and with unclassified
Rhodobacteraceae
and other genera such as
Roseobacter
,
Alteromonas
and
Vibrio
being detected at some times during both years.
Most bacteria in rotifers are not pathogenic, but detrimental effects on fish larvae can be
caused by the accumulation of bacteria in prey (Dhert
et al.
2001). Bacteria associated with
rotifer cultures have been related to unexpected mortalities or to suppressed growth in rotifers
(Harzevili
et al.
1997), as well as low survival and growth in fish larvae (Pérez-Benavente
and Gatesoupe 1988; Gatesoupe 1989; Nicolas
et al.
1989). In a survey in two different
hatcheries in Greece and in Spain, Verdonck
et al.
(1997) sampled routinely produced rotifers
(
Brachionus plicatilis
) and found
Vibrio
(
Listonella
)
anguillarum
and
Vibrio alginolyticus
as predominant bacteria, although none of the
V. anguillarum
strains were identified as
pathogenic to fish. However, it has been demonstrated that
V. anguillarum
causes crashes
in rotifer cultures (Harzevili
et al.
1997) and that rotifers can be a vector for pathogenic
Vibrio
to fish larvae, directly by ingestion or by transference from the surrounding seawater
(Prol-Garcia
et al.
2010).
16.2.3 Artemia
Artemia
are also filter feeders that ingest and digest microalgae, yeasts, bacteria, protozoans
and abiotic particles (Intriago and Jones 1993; Dhont and Lavens 1996; Makridis and Vadstein
1999). Bacteria can also adhere to their external chitinous surface of
Artemia
.
Dry
Artemia
cysts have a very low number of associated bacteria. Austin and Allen
(1982) isolated bacteria belonging to the genus
Bacillus
,
Erwinia
,
Micrococcus
,
Staphylo-
coccus
,
Vibrio
and also Gram-negative and Gram-positive rods from dehydrated cysts, and
Aeromonas
,
Bacillus
,
Micrococcus
,
Staphylococcus
, Gram-negative rods and Gram-positive
rods from cyst-hatching water. In samples from
Artemia
cysts of 26 different commercial
brands, López-Torres and Lizárraga-Partida (2001) reported that from 617 bacterial isolates
on TCBS media, 94% were Gram-positives, such as
Staphylococcus
spp. or
Micrococcus
spp.,
and only 6% were Gram-negative.
Vibrio
spp. were not detected. When cysts were hatched in
non-sterile conditions Gram-negative bacteria constituted 100% of the bacteria isolated from
TCBS medium, and
V. alginolyticus
became predominant. These results indicate that
Vibrio
are not associated with
Artemia
cysts, but are introduced during
Artemia
culture in hatcheries.
Other authors have corroborated that hatching and enrichment involve an increase of organic
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