To study if selected fish genotypes can benefit from the use of functional additives in aquafeeds to guarantee a future scenario covering the limitations on the availability of FM/FO, in terms of enhancing fish growth performance, mucosal health and disease resistance, is the aim of the present study.
Two batches of European sea bass juveniles, high growth selected (HG; selected sires x selected dams) and wildtype (WT; wild sires x selected females) populations produced at MARBEC-IFREMER, were grown at the facilities of the Parque Científico-Tecnológico Marino (PCTM) at University of Las Palmas de Gran Canaria (Telde, Canary Islands, Spain). Fish were fed a “future diet”, replacing totally FO by a combination of PO and DHA oil from algae origin and reducing by a 50% FM content by PM inclusion, until achieving the initial experimental size of 16 g. After that, fish were randomly distributed in 24 tanks of 500 L (34 fish/tank; 12 tanks by genotype; 19.0 ± 0.4 g) and supplemented with 3 different experimental functional additives (INVE, Belgium) top-coated on future diet as follows : (i) 2 weeks at high dose followed by (ii) 10 weeks at low dose. The functional additives used were a probiotic mixture (PROB), organic acids mixture (ORG) and a phytogenic (PHYTO). Diets were manufactured by Skretting (Skretting ARC, Norway) and top-coated by INVE (Belgium). Fish were sampled for gut integrity and functional microbiome and target immune parameters at the end of the total feeding trial. After each dosage feeding period, a pathogen challenge test (Vibrio anguillarum) plus stress condition (overcrowding) was applied to study the potential of additives to ameliorate the combined effect of both pathogen and stress condition.
No effects on weight gain were detected after 2 weeks of feeding in relation to the two fixed factors evaluated: genotype origin and functional diet supplemented. After 10 weeks of low dose experimental functional additives supplementation, HG fish presented a higher weight and SGR than WT fish, presenting fish the control diet higher final weight than fish fed the PROB diet within the HG genotype group.
In terms of gut microbiota, discriminant analysis did not show a clear separation among fish fed the future diet and fish fed the experimental additives regardless of the genetic background, however variations on specific taxa relative abundance were detected. For example, fish fed ORG diet presented higher relative abundance of Streptococcus in both genotypes, whereas for fish fed PHYTO this effect was observed for Lactobacillales order and in fish fed PROB presented lower abundance of Pseudomonas and Acinetobacter genera.
Funding: 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.