Effects of Host-derived Probiotics on the Growth Performance and Health of Tilapia and Carp

To address the need for well-characterised probiotic strains for tilapia and carp aquaculture, this study investigated the isolation, characterisation, and application of host-derived candidate probiotics from Nile tilapia (<i>Oreochromis niloticus</i>) and mirror carp (<i>Cyprinus carpio</i>), and their influence on growth, feed utilisation, intestinal integrity and microbiome, and mucosal health of the host.<br/>A total of 263 intestinal bacterial isolates were screened <i>in vitro</i> for antagonism against <i>Aeromonas hydrophila</i> and <i>Streptococcus iniae</i>. The top 31 isolates with inhibitory effects underwent screening against three further fish pathogens and were assessed for haemolytic activity and extracellular enzyme production <i>in vitro</i>. Isolates C61 and T70, demonstrated superior probiotic traits and were identified as strains of <i>Bacillus subtilis</i>. Both retained over 85% of their pathogen antagonism against <i>A. hydrophila</i> under simulated intestinal juice exposure while C61 showed stable and enhanced phytase specific activity under simulated gastrointestinal conditions. C61 and T70 were incorporated into diets (PT1 and PT2) at 10⁷ CFU/g and administered in Nile tilapia juveniles for 40 days. While growth did not differ significantly among treatments, PT1 fed fish exhibited increased mucosal fold height, higher goblet cell counts in the intestine and skin. <br/>In mirror carp juveniles, both live (BSpro) and heat-inactivated (BSpara) forms of C61 were tested alongside two commercial Lactobacillus paraprobiotics (Lactob1 and Lactob2) as dietary supplements under a low feeding regime. Paraprobiotic supplementation significantly altered intestinal microbial diversity and skin goblet cell coverage. Notably, Lactob1 paraprobiotic reduced intestinal <i>il1β</i> expression and skin <i>lyzc</i> relative expression, suggesting anti-inflammatory and immunoregulatory effects at the mucosal tissues.<br/>Together, these findings highlight the probiotic potential of host-derived <i>B. subtilis</i> strains as both live and inactivated bacterial feed additives for Nile tilapia and mirror carp. The bacterial feed additives have demonstrated notable influence in the intestinal microbiome, mucosal health, and immunity. <br/>

Author dc:creator

• Abarra, Sherilyn

Contributors dc:contributor

• Daniel Merrifield, Mark Rawling

Language dc:language

eng

Repository record dc:identifier

https://pearl.plymouth.ac.uk/bms-theses/472

OAI identifier oai:identifier

oai:pearl.plymouth.ac.uk:bms-theses-1471