Abstract
The reliable production of marine fish larvae is one of the major bottlenecks in aquaculture due to high mortalities mainly caused by infectious diseases. To evaluate if the compound poly-β-hydroxybutyrate (PHB) might be a suitable immunoprophylactic measure in fish larviculture, its capacity to improve immunity and performance in European sea bass (Dicentrarchus labrax) yolk-sac larvae was explored. PHB was applied from mouth opening onwards to stimulate the developing larval immune system at the earliest possible point in time. Larval survival, growth, microbiota composition, gene expression profiles and disease resistance were assessed. PHB administration improved larval survival and, furthermore, altered the larva-associated microbiota composition. The bacterial challenge test using pathogenic Vibrio anguillarum revealed that the larval disease resistance was not influenced by PHB. The expression profiles of 26 genes involved e.g. in the immune response showed that PHB affected the expression of the antimicrobial peptides ferritin (fer) and dicentracin (dic), however, the response to PHB was inconsistent and weaker than previously demonstrated for sea bass post-larvae. Hence, the present study highlights the need for more research focusing on the immunostimulation of different early developmental stages for gaining a more comprehensive picture and advancing a sustainable production of high quality fry.
Highlights
A potential biocontrol strategy is the application of poly-β-hydroxybutyrate (PHB), the polymer of the short-chain fatty acid (SCFA) β-hydroxybutyrate (β-HB)[16]
The effects of the bacterial energy storage compound PHB on sea bass yolk-sac larvae were examined with respect to survival, growth performance, immunity, microbial community and disease resistance
The focus of this study was to investigate the impact of PHB on the developing larval immune system and microbiota, when administered at the earliest possible point in time
Summary
A potential biocontrol strategy is the application of poly-β-hydroxybutyrate (PHB), the polymer of the short-chain fatty acid (SCFA) β-hydroxybutyrate (β-HB)[16]. In various aquatic organisms, including shrimps (Penaeus monodon)[19], rainbow trout (Oncorhynchus mykiss)[20] and European sea bass (Dicentrarchus labrax) juveniles[21], PHB has been demonstrated to increase survival and growth. In teleosts PHB has so far only been shown to enhance the expression of immune-related genes in sea bass post-larvae[30] and serum immune parameters as well as antibody response in adult Mozambique tilapia (Oreochromis mossambicus)[31]. It was investigated if the application of PHB modulates the immune response and the microbial community in European sea bass yolk-sac larvae. Freeze-dried PHB-accumulated bacteria (Alcaligenes eutrophus) were administered to sea bass larvae from mouth opening onwards and the effect on larval survival, growth performance, microbiota and disease resistance was assessed. An extensive analysis on the expression of genes involved in immunity, metabolism, growth and stress was performed
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