Biology Reference
In-Depth Information
less than 0.01% of the skin fl ora (Bernadsky and Rosenberg, 1992). Pond
et al. (2006) have identifi ed a strict anaerobe (
Clostridium gasigenes
)
in the
intestinal fl ora of rainbow trout. Similarly, Kim et al. (2007) have shown
the presence of
Clostridium
in the intestinal mucus. Moreover, molecular
methods have enabled a new species belonging to the genus
Mycoplasma
to be detected for the fi rst time in fi sh. It was found in abundance in the
intestine of wild and farmed salmon (Holben et al., 2002).
The worldwide shrimp market is mainly composed of the Nordic
shrimp (
Pandalus borealis
), which is only fi shed, and the tropical shrimp
(
Penaeus
sp.), which can be fi shed or farmed and whose production
has expanded rapidly in recent years. The deep-water tropical shrimp
(
Parapenaeus longirostris
)
is also found in Europe, particularly in the
Spanish and Portuguese markets.
As in fi sh, the bacterial fl ora of shrimps depends on several factors
including the species considered, the geographic location and environment,
the temperature and salinity of the water, etc. However, overall, the
same species of microorganisms are found in shrimps and in fi sh from
a given geographical zone. In fresh tropical shrimps, the initial bacterial
fl ora consists mainly of
Pseudomonas
,
Vibrio
,
Acinetobacter
,
Moraxella
,
Flavobacterium
and a high proportion of
Aeromonas
(Vanderzant et al.,
1973; Jayaweera and Subasinghe, 1988; Jeyasekaran et al., 2006). In India,
Gopal et al. (2005) have detected signifi cant amounts of different species
of
Vibrio,
including
V. parahaemolyticus
. Benner et al. (2004), working on
Nicaraguan shrimps, reported a predominance of Coryneforms and
Moraxella
followed by lower levels of
Bacillus
,
Lactobacillus
,
Micrococcus
,
Proteus
,
Shewanella,
Acinetobacter
and
Pseudomonas
. These results confi rm
those previously obtained by Matches (1982). Chinivasagam et al. (1996)
have shown the infl uence of the fi shing zone on the nature of the initial
fl ora: mostly Gram-positive bacteria on shrimps fi shed at low depths and
Pseudomonas
on those caught in deep water. The nature of this initial fl ora
has an effect on the shelf life and the organoleptic properties of shrimps
linked to spoilage.
MICROBIAL CONTAMINATION OF FLESH AND ITS
EVOLUTION DURING PRESERVATION
At fi sh death, the immune system collapses and bacteria can contaminate
the fl esh by moving through the muscle fi bres. However, bacteria are
found in much greater quantities on the skin than in the tissues and it is
more likely that the spoilage of the whole fi sh is mostly due to bacterial
enzymes that have spread through the tissues. On the other hand, the
various stages of processing (evisceration, head removal, fi lleting, and
