Poly-β-hydroxybutyrate administration during early life: effects on performance, immunity and microbial community of European sea bass yolk-sac larvae

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

Dietary effects of poly-β-hydroxybutyrate on the growth performance, digestive enzyme activity, body composition, mineral uptake and bacterial challenge of rainbow trout fry (Oncorhynchus mykiss)

This study investigated the effects of diet supplementation with poly-beta-hydroxybutyrate (PHB) on growth performance, digestive enzyme activity, lipid metabolism, mineral uptake and bacterial challenge of the rainbow trout fry (initial weight: 111.3 +/- 13.7 mg) during a 6-week experimental period. In the experimental set-up, the commercial diet of rainbow trout fry was replaced with 0.5%, 1% and 2% PHB. The results of our work showed that the replacing of diets with PHB in experimental treatments decreases the weight of rainbow trout fry during the first 2 weeks before significantly increasing final weight at the end of the 6-week period. PHB also improved digestive enzyme activity in experimental treatments. The highest total protease, pepsin activity and pancreatic enzyme secretion were observed with the 0.5% PHB treatment. A higher concentration of Na and K was observed in the whole body of the fry fed on 1% and 2% PHB-supplemented diets. Enhanced survival rates occurred in all groups of fry after bath exposure to Yersinia ruckeri compared to rates in those fed the control diet. Our results suggest that the diet supplemented with PHB may improve growth performance, digestive enzyme activity and the functioning of the immune system. These positive effects could be considered for new applications in aquaculture

Poly-beta-hydroxybutyrate (PHB) and infection reduction in farmed aquatic animals

There is a continuous effort in finding effective and sustainable strategies to control diseases in farmed animals, and in recent years, the application of the bacterial storage compound poly-β-hydroxybutyrate (PHB) was identified as a new disease control agent for aquaculture. The idea of using PHB as a biocontrol agent was conceived based on the knowledge that this biopolymer can be degraded into short-chain fatty acids (SCFAs), and SCFAs are known compounds with antimicrobial properties. At the beginning of this chapter, an overview about the PHB granule, its detection, quantification, production, and recovery in microorganisms is presented. The main topic focuses on the application and beneficial effects of PHB in farmed aquatic animals. The mechanisms by which PHB provides beneficial effects to the host are discussed

Characterizing alternative feeds for rainbow trout (O. mykiss) by 1 H NMR metabolomics

Introduction: Fish feed formulations are constantly evolving to improve the quality of diets for farmed fish and to ensure the sustainability of the aquaculture sector. Nowadays, insect, microalgae and yeast are feedstuff candidates for new feeds. However, the characterization of aquafeed is still based on proximate and targeted analyses which may not be sufficient to assess feed quality.Objectives: Our aim was to highlight the soluble compounds that specifically differ between selected plant-based feeds complemented with alternative feedstuffs and discuss their origin and potential for fish nutrition.Methods: A growth trial was carried out to evaluate growth performances and feed conversion ratios of fish fed plant-based, commercial, insect, spirulina and yeast feeds. 1H NMR metabolomics profiling of each feed was performed using a CPMG sequence on polar extracts. Spectra were processed, and data were analyzed using multivariate and univariate analyses to compare alternative feeds to a plant-based feed.Results: Fish fed insect or yeast feed showed the best growth performances associated with the lowest feed conversion ratios compared to plant-based feed. Soluble compound 1H NMR profiles of insect and spirulina alternative feeds differed significantly from the plant-based one that clustered with yeast feed. In insect and spirulina feeds, specific differences compared to plant-based feed concerned glycerol and 3-hydroxybutyrate, respectively.Conclusion: This strategy based on compositional differences between plant-based and alternative feeds can be useful for detecting compounds unsuspected until now that could impact fish metabolism