Citrus flavonoids, β-Glucan and organic acid feed additives decrease relative risk duringYersinia ruckeriO1 biotype 2 infection of rainbow trout (Oncorhynchus mykiss)

Abstract

Whether through direct supplementation of bacteria or by prebiotic supplementation thought to favour subsets of bacteria, modulation of gut microbiota constitutes an important and promising alternative to the use of prophylactic and growth promoting antibiotics in worldwide aquaculture. We fed a commercial base feed, alone or supplemented with either proprietary β-glucan, β-glucan and organic acids, citrus flavonoid or yeast cell wall supplements, to rainbow trout over a period of four weeks. Fish from each feed group were then subjected to experimental, waterborne infection with Yersinia ruckeri O1 biotype 2. Following experimental feeding, the β-glucan and organic acids supplemented group showed significantly improved feed conversion and lipid efficiency ratios. Furthermore, the β-glucan, β-glucan and organic acids and citrus flavonoid supplements proved to significantly reduce the risk of mortality in rainbow trout during experimental infection as shown by hazard ratio analysis. Resulting in 33.2%, 30.6% and 30.5% reduction in risk relative to the non-supplemented base feed, respectively, these three supplements show a promising potential either as stand-alone feed supplements, or as components in complex feed formulations. How to cite this article Rømer Villumsen K, Ohtani M, Forberg T, Tinsley J, Boye M, Bojesen AM. 2020. Citrus flavonoids, β-Glucan and organic acid feed additives decrease relative risk during Yersinia ruckeri O1 biotype 2 infection of rainbow trout (Oncorhynchus mykiss). PeerJ 8:e8706 http://doi.org/10.7717/peerj.8706 Rømer Villumsen et al. (2020), PeerJ, DOI 10.7717/peerj.8706 2/15 Tripoli E, La Guardia M, Giammanco S, Di Majo D, Giammanco M. 2007. Citrus flavonoids: molecular structure, biological activity and nutritional properties: a review. Food Chemistry . Yilmaz S, Ergun S. 2018. Trans-cinnamic acid application for rainbow trout (Oncorhynchus mykiss): I. Effects on haematological, serum biochemical, non-specific immune and head kidney gene expression responses. Fish Shellfish Immunol 78:140-157 DOI 10.1016/j.fsi.2018.04.034. Yılmaz S, Ergun S, Çelik EŞ, Yigit M. 2018. Effects of dietary humic acid on growth performance, haemato-immunological and physiological responses and resistance of Rainbow trout, Oncorhynchus mykiss to Yersinia ruckeri. Aquaculture Research 49:3338-3349 DOI 10.1111/are.13798. Yılmaz S, Ergun S, Yigit M, Çelik EŞ. 2019. Effect of combination of dietary Bacillus subtilis and trans-cinnamic acid on innate immune responses and resistance of rainbow trout, Oncorhynchus mykiss to Yersinia ruckeri. Aquaculture Research 51(2):441-454 DOI 10.1111/are.14379. Ytrestøyl T, Aas TS, Åsgård T. 2015. Utilisation of feed resources in production of Atlantic salmon (Salmo salar) in Norway. Aquaculture 448:365-374 YJ. 2014. Efficacy and tolerance of yeast cell wall as an immunostimulant in the diet of Japanese seabass (Lateolabrax japonicus). Aquaculture 432:217-224

Effects of increasing dietary level of organic acids and nature-identical compounds on growth, intestinal cytokine gene expression and gut microbiota of rainbow trout (Oncorhynchus mykiss) reared at normal and high temperature

“…Pandey [41] reported consistent better growth and mineral utilization in rainbow trout fed for 12 weeks with low fishmeal-based (15%) diets supplemented with different OA at 1% (citric, lactic, fumaric, formic and acetic), especially for citric and fumaric acid. More recently, Villumsen [42] found that the dietary supplementation of organic acids and β-glucan showed improved FCR and LER in rainbow trout juveniles after 37 days feeding. The work mentioned suggested that improved performance and digestibility of OA supplementation may be explained by lowered pH resulting in a higher dissociation of mineral compounds, reduced rate of gastric emptying and formation of chelated mineral complexes that can be easily absorbed.…”

Synbiotic feed supplementation significantly improves lipid utilization and shows discrete effects on disease resistance in rainbow trout (Oncorhynchus mykiss)

“…While the outer peel of citrus fruits have been shown to generally contain the highest concentrations of flavonoids, citrus peel essential oils remain a crude mix of many components 57 , 58 . In a recent study, prebiotic supplementation with citrus flavonoids alone had no apparent effects on weight gain, FCR, SGR, LER or PER in rainbow trout 26 . A plausible explanation for the improved LER observed in this study, could be the additional inclusion of probiotics, providing a synergistic improvement of lipid utilization.…”

“…Citrus flavonoids have been suggested to conduct an antimicrobial activity against Gram-negative bacteria 63 , as well as suppression of bacterial mechanisms involved in infection 64 . Furthermore, a previous study has shown that citrus flavonoid supplemented feed conferred a significant reduction in relative risk in trout following a similar waterborne infection with Y. ruckeri 26 . Rodriguez-Estrada et al have previously demonstrated a seemingly dose-dependent reduction in mortality in rainbow trout fed MOS, inactivated E. faecalis or a combination of both following intraperitoneal injection of A. salmonicida 34 .…”

“…Citrus flavonoids have been suggested to conduct an antimicrobial activity against Gram-negative bacteria 63 , as well as suppression of bacterial mechanisms involved in infection 64 . Furthermore, a previous study has shown that citrus flavonoid supplemented feed conferred a significant reduction in relative risk in trout following a similar waterborne infection with Y. ruckeri 26 . Rodriguez-Estrada et al .…”

“…This includes postitive effects on different feed performance parameters following supplementation with a variety of compounds, including yeast cell wall components. Examples include yeast cell wall supplementation of Japanese seabass ( Lateolabrax japonicus ) 17 , fructose- and mannose-oligosaccharide (MOS) supplementation in Atlantic salmon ( Salmo salar ) 18 , as well as both MOS supplementation 19 – 21 and incorporation of various organic acids in rainbow trout feeds either alone 22 – 25 , or in combination with β-glucans 26 . In addition to this, improved disease resistance towards bacterial infection has been reported for yeast cell wall supplements in Japanese seabass 17 , as well as citrus flavonoid, β-glucan, co-supplementation of β-glucan and organic acids in rainbow trout 26 – 28 .…”