Probiotic, prebiotic and synbiotic applications for the improvement of larval European lobster (Homarus gammarus) culture

Abstract

The effects of dietary applications of a commercial probiotic (Bacillus spp.) and prebiotic (mannan oligosaccharides [MOS]), used singularly and combined (i.e. synbiotic), on larval survival, growth, intestinal microbial communities and stress resistance of larval European lobster, Homarus gammarus, were assessed. Larvae were reared in green water culture for 12days from hatch until metamorphosis to zoea III. Un-supplemented Artemia nauplii (control) or Artemia nauplii enriched with probiotics (Bacillus spp. 100mgl−1), prebiotic (MOS 12mgl−1) or synbiotics (100mgl−1Bacillus spp.+MOS 12mgl−1) were each fed to 3 replicate groups of zoea I lobsters for 12days. The effects on gut microbiota were assessed using culture-dependent methods at 1, 7 and 12days post-hatch (dph) and PCR-DGGE at 1 and 12dph. PCR-DGGE was also used to assess microbial communities of the live feeds. Carapace length and weight of five H. gammarus from each replicate was recorded on 1, 7, and 12dph and survival to zoea III was recorded. A low salinity stress test was used as a measure of organism fitness at day 12.After 12dph, H. gammarus larvae fed experimental treatments had significantly (P<0.02) improved weight, carapace length and weight gain, compared to larvae fed control treatments. Survival to 12dph was elevated by all treatments and was significantly (P<0.001) increased for the Bacillus and MOS fed larvae. Salinity stress tolerance was greatest in larvae fed Bacillus although all experimental treatments produced enhanced tolerance to salinity stress in comparison to larvae fed control treatment. Culture-dependent analysis of the gut microbiota of larval lobsters demonstrated the colonisation of Bacillus spp. in larvae fed probiotic or synbiotic enriched live feeds. There was also a reduction in Vibrio levels in certain biotic fed larvae and live feed treatments. PCR-DGGE revealed that the number of observed taxonomical units (OTUs), species richness and species diversity increased in zoea III lobsters fed probiotic, prebiotic and synbiotic. Subsequently, the microbial profiles were dissimilar to the control group with the synbiotic group showing the greatest dissimilarity to the control (36.54±2.54%). The similarity between bacterial communities associated with Artemia and zoea III larvae was highest in the Bacillus treatments (53.86%). The present study demonstrates the benefit of applying dietary supplementation of Bacillus, MOS and Bacillus+MOS on the GI microbiota of lobster larvae which subsequently improved growth performance and stress tolerance.