Poly-ß-hydroxybutyrate supplementation enhances growth and immune responses of juvenile Nile tilapia (Oreochromis niloticus)

Authors: SUEHS, BLAINE - Texas A&M University; YAMAMOTO, FERNANDO - Mississippi State University; Older, Caitlin; ASIRI, FAHAD - Kuwait Institute For Scientific Research; GATLIN III, DELBERT - Texas A&M University

Submitted to: Aquaculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/21/2024
Publication Date: 7/23/2024
Citation: Suehs, B.A., Yamamoto, F.Y., Older, C.E., Asiri, F., Gatlin 111, D.M. 2024. Poly-ß-hydroxybutyrate supplementation enhances growth and immune responses of juvenile Nile tilapia (Oreochromis niloticus). Aquaculture. 594:741384. https://doi.org/10.1016/j.aquaculture.2024.741384.
DOI: https://doi.org/10.1016/j.aquaculture.2024.741384

Interpretive Summary: Development of new methods to treat and prevent bacterial infections in fish farming has received considerable attention in recent years due to frequent bacterial disease outbreaks in modern intensive aquaculture. Poly-ß-hydroxybutyrate (PHB) is a biopolymer synthesized by some bacteria with potential benefits for fish, including enhancing the immune response and protecting the host against pathogenic bacteria. Scientists at Texas A&M University and the Kuwait Institute for Scientific Research, in collaboration with scientists at the USDA ARS Warmwater Aquaculture Research Unit evaluated the potential of PHB as an immunomodulator in Nile tilapia. Immune cells obtained from the head kidney of Nile tilapia demonstrated enhanced activity with increasing levels of a PHB precursor, 3-hydroxybutryate (3HB). PHB-synthesizing bacteria Zobellella denitrificans ZD1 were supplemented to a control diet five experimental diets containing PHB in stepwise increments (0.125, 0.25, 0.5, 1.0, and 2.0% of dry-diet weight). Nile tilapia fed these diets exhibited enhanced growth with increasing PHB inclusion in the diet. Finally, PHB supplemented diets also affected the bacterial communities present in the gut. These results indicate PHB supplementation in Nile tilapia diets can have positive effects on fish growth and immune response, and warrants further research into its use as a novel method of treatment and/or prevention of bacterial disease outbreaks.

Technical Abstract: Development of alternative disease treatment and prevention strategies has received considerable attention in recent years due to frequent epizootic outbreaks in modern intensive aquaculture. Poly-ß-hydroxybutyrate (PHB) is a biopolymer synthesized by some bacteria with potential immunostimulatory effects. This study analyzed the potential of PHB as an immunomodulator in juvenile Nile tilapia utilizing in vitro and in vivo approaches. Head kidney-derived macrophage production of intra- and extra-cellular superoxide anion exhibited significant linear and quadratic relationships with graded doses (0.0, 0.5, 1.0, 2.0, 4.0 and 8.0 mM) of a PHB precursor, 3-hydroxybutryate (3HB). Additionally, lyophilized PHB-synthesizing bacteria, Zobellella denitrificans (ZD1), were supplemented to a practical basal diet for Nile tilapia (36% crude protein and 6% crude lipid) to produce five isonitrogenous and isolipidic experimental diets containing PHB in five stepwise increments (0.125, 0.25, 0.5, 1.0, and 2.0% of dry-diet weight). After termination of the feeding trial, Nile tilapia exhibited dose-dependent linear and quadratic relationships in percentage weight gain, as well as feed efficiency, protein conversion efficiency, and hepatosomatic index. Finally, PHB-supplemented diets did significantly modulate intestinal microbiota composition. In conclusion, Nile tilapia exhibited enhanced growth parameters, condition factors, immunological responses, and intestinal microbiota modulation when fed PHB, with the optimal inclusion level determined to be 1% of dry diet.