Agriculture Reference
In-Depth Information
Roseobacter
clade are predominant in marine plankton and that some species are able to form
biofilms and colonize surfaces (Slightom and Buchan 2009) would explain the predominance
of those phylotypes.
Pathogenic strains of
Vibrio cholerae
,
Vibrio parahaemolyticus
,
Vibrio vulinificus,
,
V. algi-
nolyticus
and
Aeromonashydrophila
have been isolated from copepods, which present a risk of
introducing harmful bacteria to larvae, as well as humans (Rawlings
et al.
2007; Gugliandolo
et al.
2008).
16.3 BACTERIAL CONTROL OF LIVE FEED CULTURES
The reduction of the bacterial load in zooplanktonic organisms is essential in the successful
rearing of marine fish larvae for two main reasons:
(1) Live feed organisms are added daily in large amounts to the rearing tanks, promoting the
accumulation of associated bacteria. This fact may result in serious deterioration of the
environmental culture conditions due to respiration of bacterial population and accumu-
lation of their excretory products.
(2) In most cases, the microbiota associated with live feed includes opportunistic bacteria,
which may be harmful to the larvae under certain conditions, causing increased mortalities.
Surface-attached bacteria in prey can be removed by washing procedures but bacteria
could still remain in the GI tract. Freshwater, ozone, sodium hypochlorite, hydrogen peroxide,
formaldehyde, sodium nifurstyrenate, and various antibiotics have been tested for the
reduction of the bacterial load in rotifers and
Artemia
(Tanasomwang and Muroga 1992;
Tolomei
et al.
2004; Giménez
et al.
2006). Most of these treatments are very effective in the
reduction of the bacterial load of live prey, though the effect of residues of some compounds,
such as hypochlorite and formaldehyde, on the viability of fish larvae is often unknown. The
use of antibiotics should be avoided due to the high risk of increasing antibiotic resistance in
bacterial communities.
UV light has been tested at experimental scale for rotifer disinfection, showing a quite
high efficiency and eliminating more than 90% of viable bacterial counts (Munro
et al.
1999).
However, the efficiency of UV light is highly influenced by the presence of particles in the
water. Therefore, upscaling could be problematic in routine operations at industrial scale as
rotifer cultures should be particle-free.
Ozone is applied to disinfection areas, inlow waters, eggs or live feed (Suantika
etal.
2001).
The advantage of ozone is that it counteracts viral infections as well as bacterial pathogens.
However, ozonation conditions must be carefully controlled to avoid problems with excessive
production of oxygen radicals. In addition, ozonation must take place in well-aerated areas of
the hatcheries as ozone inhalation by personnel can cause health problems.
The application of natural products, such as essential oils of various plants with
antimicrobial properties (phytobiotics), is another new and interesting approach (Stefanakis
et al.
2011). The advantages of such products are that the appearance of resistant strains is
less probable, and that their application will not have a negative effect on the public image of
the aquaculture industry.
Although the reduction of bacterial load has advantages, several studies have demonstrated
that the microbial community present in live feed also contributes to the success of live feed
Search WWH ::
Custom Search