Poly-β-hydroxybutyrate has limited effects on growth and immune responses of juvenile hybrid striped bass Morone chrysops × M. saxatilis, and red drum Sciaenops ocellatus based on in vivo and in vitro approaches.

Disease outbreaks in intensive aquaculture, particularly from bacterial pathogens, represent major constraints to efficient fish production. Therefore, development of novel disease treatment and prevention strategies have been receiving considerable attention in recent years. This study analyzed the efficacy of the organic acid poly-β-hydroxybutyrate (PHB) as an immunomodulator in hybrid striped bass (Morone chrysops × M. saxatilis) (HSB) and red drum (Sciaenops ocellatus) based on both in vitro and in vivo approaches. In vitro immunological assays, namely intra- and extra-cellular superoxide anion production and bactericidal capacity of HSB head kidney-derived leukocytes were determined to be significantly (P < 0.05) reduced when graded doses of sodium 3-hydroxybutyrate (3HB; 0.0, 0.5, 1.0, 2.0, 4.0 and 8.0 mM), a precursor to PHB, was supplemented in the cell culture media. For the HSB in vivo feeding trial, PHB-synthesizing bacteria, Zobellella denitrificans (ZD1), were supplemented to basal diets to produce five isonitrogenous and isolipidic experimental diets (40% crude protein and 10% crude lipid) containing PHB in stepwise increments (0.0, 0.125, 0.25, 0.5, 1.0, and 2.0% of dry-diet weight). In addition, a control diet was supplemented with 0.5% of a commercial purified PHB product. In a separate feeding trial, a commercial PHB product was supplemented to a practical basal diet in stepwise increments (0.0,0.125, 0.25, 0.5, and 1.0%) to isonitrogenous and isolipidic experimental diets (40% crude protein and 10% crude lipid). Juvenile HSB, and red drum (∼5.5, and 4.4 g/fish initial weight, respectively) in separate feeding trials were stocked in 38-L aquaria operated as a recirculating aquaculture systemHSB experimental diets were randomly assigned to quadruplicate aquaria of fish while the red drum experimental tdiets were randomly assigned to quintuplicate aquaria and fed for an 8-week period. HSB and red drum exhibited limited responses to graded levels of PHB, including percentage weight gain, feed efficiency, protein conversion efficiency and hepatosomatic index. Only juvenile red drum showed significantly (P < 0.05) increased muscle yield values with increasing dietary PHB while whole-body proximate composition analyses revealed no significant (P > 0.05) differences, except for HSB whole-body crude lipid. Thus, PHB (ZD1-derived and commercial) had limited effects on growth parameters, body condition factors, and immunological responses of both HSB and red drum juveniles. • 3-hydroxybutyrate (3HB) decreased measured innate immune responses of hybrid striped bass head kidney-derived leukocytes in vitro. • PHB supplementation had limited responses on growth performance and whole-body composition of juvenile hybrid striped bass and red drum. • Red drum exposed to a Photobacterium infection had higher survival when supplemented with the PHB ingredient than fish fed the basal treatment. [ABSTRACT FROM AUTHOR]