Live Feeds: Microbial Assemblages, Probiotics and Prebiotics - Aquaculture Nutrition: Gut Health, Probiotics and Prebiotics - page 436

on the number (CFU) of total viable bacteria or culturable Vibrio levels in lobster larvae.
However, PCR-DGGE profiles of MOS-treated larvae were dissimilar to control, even though
richness (Margalef species richness) and diversity (Shannon index) showed similar values.
Therefore, the addition of the prebiotic alone exerted an effect, modifying the indigenous bac-
terial community. When MOS and Bacillus spp. were added together, more dissimilar profiles
and reductions in richness and diversity were observed.
16.8 CONCLUSIONS AND FUTURE PERSPECTIVES
Bacteria in live feeds have a major influence on the microbiota of marine fish larvae, and live
feed can be the mode of entry of specific pathogens or non-specific opportunistic bacteria to the
larvae. Environmental and health concerns have resulted in a progressive reduction of the use
of chemotherapeutics and to the search for alternatives, which should be based on considering
bacteria as an active part of the rearing ecosystems.
The development of strategies for microbial control in live feeds will rely on knowledge of
their microbiotas and the microbial interactions with fish larvae and rearing systems, as well as
host-bacterial interactions. Tailored solutions should be developed for each case. Probiotics
and prebiotics (or combined as synbiotics) are suitable tools to enhance particular bacterial
groups and to prevent infection by identified pathogens. When the aim is to improve feed
cultures or to control the bacterial microbiota in feeds, isolation of autochthonous probiotic
bacteria in live feeds will favour co-culture and colonization of the feed. Bioencapsulation of
probiotics in live feeds, prior to their delivery to fish larvae, would be a more useful tool when
probiotics are isolated from the natural microbiota of the gut of the target larval species.
Studies of probiotics, prebiotics or immunostimulants should involve a multidisciplinary
approach including the study of: (1) the influence in host survival and growth parameters, (2)
the presence of the probiotic and the modification of the microbial community of the host or
of the surrounding water, and (3) the impact on host immunological parameters. The use of
live feed gnotobiotic cultures, combined with new molecular techniques, is giving new insight,
improving our knowledge of microbial ecology and host-microbe interactions, and helping
to elucidate underlying mechanisms.
The use of probiotics and prebiotics will constitute a strategy to improve the fitness of
new live feeds, such as copepods, helping to upscale to industrial levels. Bioencapsulation
of probiotics in copepods must also be explored. Particular research should be conducted on
stable co-cultures of probiotics with microalgae, both for the feeding or enrichment of live
feeds and for direct addition to larvae.
The application of prebiotics in aquaculture may have advantages over probiotics in terms
of production and preserving costs, and in the context of regulatory issues as a consequence
of avoiding the use of live microorganisms (Ringø et al. 2010). The possibility of incorpo-
rating prebiotics to extruded dry feeds has great potential to increase live feed production, by
modulating microbial communities and controlling the development of detrimental bacteria.
However, research is necessary to document and understand the effects of prebiotics on the
microbiota of live prey. Also, as described above, live prey have been demonstrated to be an
effective way of delivering prebiotics to larvae (Daniels et al. 2010) and more research should
be conducted on this topic.