Biology Reference
In-Depth Information
Biofi lters
In aquaculture, the concept of probiotics has been extended to bacteria
which can exert their benefi cial effect on the host by modifi cation of the
microbial community associated with fi sh or water, improving the quality
of the environment (Verschuere et al., 2000). Thus, strategies of water
treatment with addition of benefi cial bacteria would also be included.
Recirculating aquaculture systems (RAS) are the latest form of the
fi sh farming production system, more adapted to fulfi l environmental
constraints (e.g., generating low emissions or making coastal location
unnecessary). RAS are typically an indoor system that allows farmers to
control environmental conditions all-year round, considered better than
conventional fl ow-through systems from an environmental (Neori et al.,
2007) and bio-security (Pruder, 2004) point of view. In the last few years,
RAS systems have being investigated for cultivation of different species
of fi sh larvae (Faulk and Holt, 2005; Martins et al., 2009). Water quality of
aquaculture facilities equipped with RAS is maintained by a diversity of
microbial community associated with biofi lters (Gross et al., 2003; Sugita
et al., 2005; Michaud et al., 2006). Recirculation of water tends to stabilize
the microbial community and make it more persistent to perturbations
(Attramadal et al., 2005). Biofi lters colonized with non-opportunistic
bacteria have been previously used for production of matured water,
which increased survival of Atlantic halibut yolk sac larvae (Skjermo et
al., 1997) and improved the growth of turbot larvae (Salvesen et al., 1999)
by improving microbial water quality.
Some probiotic bacteria with antagonistic activity towards fi sh pathogens
also have the ability to produce biofi lms. Alpha proteobacteria belonging to
the
Roseobacter
clade
have shown to produce tropodithietic acid (Brinkhoff
et al., 2004; Bruhn et al., 2005; Porsby et al., 2008), which inhibits different
bacterial groups (Brinkhoff et al., 2004), including some fi sh pathogens
(Ruíz-Ponte et al., 1999; Bruhn et al., 2005; Porsby et al., 2008). Production of
this antibiotic is related to the attachment of the probiotic to surfaces and to
biofi lm formation (Bruhn et al., 2007; Porsby et al., 2008). Therefore, biofi lters
could be inoculated and colonized by biofi lm-forming probiotic bacteria,
improving the permanence of probiotics in the rearing system and protecting
the larvae against opportunistic and potential pathogenic bacterial strains.
Inhibiting or Inactivating Detrimental Bacteria in the System
Bacteriophages
Bacteriophages are viruses that infect bacteria. It has been suggested that in
nature bacteriophages are one of the main causes of mortalities in bacterial
populations. The principle in using bacteriophages in aquaculture is their
application for the control of bacterial diseases (Imbeault et al., 2006; Park
et al., 2000). The advantage of such a strategy is avoiding the of use of
