Genetically superior European sea bass (Dicentrarchus labrax) and nutritional innovations: Effects of functional feeds on fish immune response, disease resistance, and gut microbiota

The objective of this study was to determine if selected fish genotypes could benefit from the use of functional additives in novel aqua feed formulations to improve growth performance, gut microbiota, immune response, and disease resistance in fish. Two batches of juvenile European sea bass selected for high growth (HG; selected sires x selected dams), and wild types (WT; wild sires x selected females) were fed a “future diet” coated with three different functional additives for 12 weeks as follows: (i) 2 weeks with a high dose, followed by (ii) 10 weeks with a low dose. The functional additives tested were a mixture of probiotics (PROB), organic acids (ORG), and phytogens (PHYTO). A pathogen challenge test (Vibrio anguillarum) and a stress condition (overcrowding) were performed after each dose. At the end of the feeding experiment, fish from the HG group performed better than fish from the WT group in terms of body weight, relative growth, SGR, and DGI. The results of the two challenge tests performed after two weeks of high dose and ten weeks of low dose showed a significant effect of diet on fish survival. GALT-associated gene expression analysis revealed an interaction between the genotype and diet for il-1β in the distal gut. Finally, regarding the gut microbiota, discriminant analysis showed no clear separation between fish fed the future diet and those fed the same diet with experimental additives. Nevertheless, the relative abundance of certain taxa varied between experimental groups. For example, fish fed the ORG diet had higher relative abundance of Streptococcus in both genotypes, whereas fish fed the PHYTO diet had higher abundance of Lactobacillales. In contrast, fish fed PROB had lower abundance of Pseudomonas and Acinetobacter.The current study was supported by the EU Horizon 2020 AquaIMPACT (Genomic and nutritional innovations for genetically superior farmed fish to improve efficiency in European aquaculture), number: 818367.info:eu-repo/semantics/publishedVersio

Managing input C/N ratio to reduce the risk of Acute Hepatopancreatic Necrosis Disease (AHPND) outbreaks in biofloc systems : a laboratory study

Biofloc systems are microbial mature environments that are potentially less conducive disease outbreaks. We hypothesized that the way in which biofloc microbial communities are managed determines the level of disease protection. To investigate such hypothesis, Litopenaeus vannamei post-larvae were cultured for 21 days in biofloc environments created by different water management procedures. Five different types of bioflocs were created: autotrophic bioflocs without probiotics, autotrophic bioflocs with probiotics, heterotrophic bioflocs without probiotics, heterotrophic bioflocs with probiotics, and a flow-through system as a control. Heterotrophic bioflocs were obtained by daily addition of carbon (glucose) at an estimated C/N ratio of 18 throughout the experiment. For autotrophic bioflocs this input of carbon was applied only to start up the system and upon appearance of bioflocs (TSS > 100 mg L-1) and a drop in total ammonium nitrogen concentration below 0.05 mg L-1, carbon dosing was stopped. Bioflocs cultured with addition of probiotics received a 0.5 ppm dose every 48 hours. After 21-d culture period, a 96 h challenge test was performed with a Vibrio parahaemolyticus strain known to cause AHPND. For each biofloc type, this challenge was performed in three different approaches: 1- Shrimp were taken out of their biofloc tanks and challenged by applying new seawater; 2-Shrimp from biofloc tanks were challenged in their respective biofloc suspensions; and 3- Non-experimental shrimp, randomly selected from a recirculation (RAS) system were challenged in the types of biofloc suspensions. Mortality was high when shrimp were challenged in new seawater, independent of treatment. When challenged in their respective biofloc suspensions shrimp survival was the highest in heterotrophic bioflocs with and without probiotic supplementation and the autotrophic bioflocs with probiotics, whereas shrimp survival in autotrophic bioflocs without probiotics was 50%. These results were similar when non-experimental shrimp originating from a RAS system were challenged in these biofloc suspensions. Taken together, results suggest that bioflocs as such can decrease the impact of a Vibrio parahaemolyticus challenge and that this protection depends on the operational parameters of the biofloc system. Moreover, probiotics can be used to complement the protective effect of bioflocs. This information reinforces the importance of microbial community management as a tool to reduce the risk of disease and establish highly biosecure systems

Long-term sulphide mitigation through molybdate at shrimp pond bottoms

<p>Shrimp are commonly cultured in earthen aquaculture ponds where organic-rich uneaten feed and faeces accumulate on and in the sediment to form anaerobic zones. Since the pond water is rich in sulphate, these anaerobic conditions eventually lead to the production of sulphide. Sulphides are toxic and even lethal to the shrimp that live on the pond sediment, but physicochemical and microbial reactions that occur during the accumulation of organic waste and the subsequent formation of sulphide in shrimp pond sediments remain unclear. Molybdate treatment is a promising strategy to inhibit sulphate reduction, thus, preventing sulphide accumulation. We used an experimental shrimp pond model to simulate the organic waste accumulation and sulphide formation in a long-term experiment (61 days). Sodium molybdate (5 and 25 mg/L Na2MoO4.2H2O) was applied as a preventive strategy to control sulphide production before oxygen depletion. Molybdate addition mitigated H2S production in the sediment, and delayed its transfer to the bulk liquid by pushing the higher sulphide concentration zone towards deeper sediment layers. Molybdate treatment at 25 mg/L significantly impacted the overall microbial community composition and treated samples (5 and 25 mg/L molybdate) had about 50% higher relative abundance of sulphate reducing bacteria than the control (no molybdate) treatment. In conclusion, molybdate worked as long-term mitigation strategy against sulphide accumulation by directly steering the microbial community in a shrimp pond system.</p&gt

Genetically superior European sea bass (Dicentrarchus labrax) and nutritional innovations: Effects of functional feeds on fish immune response, disease resistance, and gut microbiota

The objective of this study was to determine if selected fish genotypes could benefit from the use of functional additives in novel aqua feed formulations to improve growth performance, gut microbiota, immune response, and disease resistance in fish. Two batches of juvenile European sea bass selected for high growth (HG; selected sires x selected dams), and wild types (WT; wild sires x selected females) were fed a “future diet” coated with three different functional additives for 12 weeks as follows: (i) 2 weeks with a high dose, followed by (ii) 10 weeks with a low dose. The functional additives tested were a mixture of probiotics (PROB), organic acids (ORG), and phytogens (PHYTO). A pathogen challenge test (Vibrio anguillarum) and a stress condition (overcrowding) were performed after each dose. At the end of the feeding experiment, fish from the HG group performed better than fish from the WT group in terms of body weight, relative growth, SGR, and DGI. The results of the two challenge tests performed after two weeks of high dose and ten weeks of low dose showed a significant effect of diet on fish survival. GALT-associated gene expression analysis revealed an interaction between the genotype and diet for il-1β in the distal gut. Finally, regarding the gut microbiota, discriminant analysis showed no clear separation between fish fed the future diet and those fed the same diet with experimental additives. Nevertheless, the relative abundance of certain taxa varied between experimental groups. For example, fish fed the ORG diet had higher relative abundance of Streptococcus in both genotypes, whereas fish fed the PHYTO diet had higher abundance of Lactobacillales. In contrast, fish fed PROB had lower abundance of Pseudomonas and Acinetobacter