Gastrointestinal microbiota have an important impact on fish health and disease, stimulating interest in a better understanding of how these gastrointestinal microbial communities are composed and consequently affect host fitness. In this respect, probiotic microorganisms have been extensively used in recent aquaculture production. To study the use of probiotics in the treatment of infectious diseases, the establishment of a method of experimental infection to obtain consistent results for mortality and infection in challenge tests is important. In pathogen-screening tests, 4 candidate pathogenic bacteria strains (Edwardsiella ictaluri gly09, E. ictaluri gly10, E. tarda LMG2793 and Streptococcus agalactiae LMG15977) were individually tested on xenic Nile tilapia larvae. Only Edwardsiella strains delivered via Artemia nauplii, with or without additional pathogen delivery via the culture water, led to increased mortality in fish larvae. A gnotobiotic Nile tilapia larvae model system was developed to provide a research tool to investigate the effects and modes-of-action of probiotics under controlled conditions. A double disinfection procedure using hydrogen peroxide and sodium hypochlorite solution was applied to the fish eggs, which were subsequently incubated in a cocktail of antibiotic and antifungal agents. In the gnotobiotic challenge test, E. ictaluri gly09R was added to the model system via Artemia nauplii and culture water, resulting in a significant mortality of the gnotobiotic fish larvae. The developed gnotobiotic Nile tilapia model can be used as a tool to extend understanding of the mechanisms involved in host-microbe interactions and to evaluate new methods of disease control.

Shrimp is an important food source consumed worldwide. An intensive aquaculture system with overuse of feed in combination with detrimental effects from climate change are serious problems leading to mass mortality of cultured shrimp. Biofloc technology is an approach to managing water quality and controlling the disease to counter the negative side of intensive culture system; however, most of the biofloc applications are naturally formed, which could be inconsistent. In this study, we employed an established optimal ratio of microbial consortium called “ex-situ biofloc (BF)” to be used as a feed supplement in shrimp cultured in a zero-water discharged system at low salinity conditions. Three feeding groups (100%commercial pellet (C), 95%C+BF, 90%C+BF) of shrimp were cultured for six weeks. The effect of an ex-situ biofloc supplement with commercial pellet reduction showed that levels of ammonium, nitrite, nitrate and phosphate were significantly decreased in water culture. Shrimp fed with ex-situ biofloc supplement with commercial pellet reduction exhibited significantly increased shrimp weight and survival, and significantly expressed growth-related genes involving lipolysis and energy metabolism higher than those fed with 100% commercial pellet. Nutritional analysis indicated a significant increase of docosahexaenoic acid (DHA) and eicosenoic acid (C20:1) concentrations in the ex-situ biofloc supplemented shrimp. This finding revealed the potential of ex-situ biofloc to manage water quality, improve shrimp growth performance and enhance shrimp nutritional value under intensive culture at low salinity conditions. The beneficial effects of the ex-situ biofloc in shrimp culture system make it a promising alternative strategy to mitigate climate change effects leading to the sustainable production of high-quality shrimp in the future.

The high losses in shrimp production due to mortality caused byVibrioopportunistic pathogens still constitute a significant challenge in the shrimp industry. Synbiotic feed supplementation appears to be a promising control strategy to maintain healthy shrimp stock. In this study, the effects of synbiotic-containing prebiotic seaweedsKappaphycus alvareziiandSpirulinasp. as well as probioticHalomonas alkaliphilawere evaluated on the survival, growth, and vibriosis ofLitopenaeus vannameiduring the post-larval stage. Five different feeds were tested: commercial feed, prebioticsK. alvareziiandSpirulinasp.-supplemented feed, and synbiotic-supplemented feed usingK. alvarezii, Spirulinasp. and probioticH. alkaliphilawith different concentrations of 10⁸, 10⁹, and 10¹⁰CFU.kg⁻¹. Following 14 days after the feeding test, the highest shrimp survival (91.46 ± 0.05%) was obtained in the treatment group fed with synbiotic-supplemented feed containing 0.375%K. alvarezii, 0.125%Spirulinasp., andH. alkaliphilaat 10⁹CFU.kg⁻¹(p< 0.05). A 7-day challenge test against opportunistic bacteriaVibrio harveyiiwas then performed using three treatment groups: (1) synbiotic, containing 0.375%K. alvarezii, 0.125%Spirulinasp., andH. alkaliphilaat 10⁹CFU.kg⁻¹; (2) prebiotic, with 0.375%K. alvarezii, 0.125%Spirulinasp.; and (3) control, using commercial feed. The highest shrimp survival of (79.9 ± 0.05%) was found in the synbiotic treatment group, followed by the prebiotic and control treatment groups (p< 0.05). Overall results suggested that synbiotic-supplemented feed containing 0.375%K. alvarezii, 0.125%Spirulinasp., andH. alkaliphilaat 10⁹CFU.kg⁻¹significantly improved shrimp survival even when challenged withV. harveyii. Thus, this synbiotic can be potentially applied as an alternative biocontrol strategy against vibriosis in intensive shrimp post-larval culture.