Biology Reference
In-Depth Information
gut of reared animals. Microorganisms that are capable of protecting the
host against harmful pathogens are called probionts. While a large amount
of probiotic research has been done with farm animals and humans, there
is comparatively less research on aquatic animals (Austin and Brunt, 2009)
and even less in the larval culture of these animals. Much of the work
done in aquaculture provides little or no evidence on the role of probiotic
microorganisms inside the host, but there is scientifi c evidence that also
proves that some bacteria are capable of limiting the action of pathogens.
In Chapter 1, Pintado and his colleagues have discussed several new
strategies including the use of prebiotics and probiotics in marine fi sh
larval rearing. This chapter deals exclusively on the use of probiotics in
the larval culture of aquatic animals.
DEFINITIONS
Probiotics
The defi nition of probiotics has evolved mainly by the study of farm
animals or humans, terrestrial animals, but not necessarily applicable
to aquatic animals. Fuller (1989) proposed the defi nition of a probiont
as “a live microbial feed which benefi cially affects the host animal by
improving its intestinal balance”. Because there is a strong interaction
between the organism and its aquatic environment, an environment
where opportunistic pathogens can and do grow, the defi nition has to
also encompass this environment. A general defi nition of probiotic that
takes into account the environment has been proposed by Verschuere
and collaborators (2000)—“a live microbial adjunct which has a benefi cial
effect on the host by modifying the host-associated or ambient microbial
community, by ensuring improved use of the feed or enhancing its
nutritional value, by enhancing the host response towards disease, or by
improving the quality of its environment”. This defi nition incorporates
new properties that might not be associated with a probiont, as advised
by Gomez-Gil et al. (2000), a probiont should not be confused with a feed
additive, such as a growth promoter, nor a bioremediation agent. The
principal goal of a probiont is to eliminate a pathogenic treat, diminish it,
or to enhance the immunological response of the host to it. Therefore, the
defi nition of Verschuere et al. (2000) can be simplifi ed to “a live microbial
adjunct, which has a benefi cial effect on the host by modifying the host-
associated or ambient microbial community and so enhances the host
response towards disease”. The microbe should not only be alive, but it
should be kept alive (Gatesoupe, 1999). If the microbes are dead, then they
can be considered as feed additives due to their passive action. It is desired
that they actively enhance the host's response towards disease by means
of colonization, production of metabolites, etc.
