| dc.description.abstract | Disease outbreaks in intensive aquaculture, particularly from bacterial pathogens, represent major constraints to efficient fish production, necessitating development of novel and innovative disease treatment and prevention strategies. Poly-β-hydroxybutyrate (PHB), a biopolymer synthesized by specific gram-negative and gram-positive bacteria, is a compound with potential immunostimulatory capabilities for various fish species. This study analyzed the efficacy of PHB as an immunomodulator in Nile tilapia, hybrid striped bass (HSB), and red drum based on both in vitro and in vivo approaches. In vitro immunological assays, namely intra- and extra-cellular superoxide anion production of head-kidney-derived macrophages exhibited significant (P<0.05) linear and quadratic relationships when graded doses of 3-hydroxybutryate (3HB) (0.0, 0.5, 1.0, 2.0, 4.0 and 8.0 mM) were added to Nile tilapia cells in culture media. In contrast, 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 identical graded doses of 3HB was supplemented in the cell culture media. For the in vivo feeding trials, PHB-synthesizing bacteria, Zobellella denitrificans, were produced on-site at the Texas A&M Aquacultural Research and Teaching Facility and then supplemented to species-specific basal diets to produce five isonitrogenous and isolipidic experimental diets containing PHB in stepwise increments (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. Juvenile Nile tilapia, HSB, and red drum (~ 1.3, 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 system, complete with settling chamber, biological and sand filtration, and UV sterilization. Each of the experimental diets was randomly assigned to quadruplicate aquaria of fish and fed for an 8-week period. Nile tilapia exhibited significant (P<0.05) dose-dependent linear and quadratic relationships with regard to percentage weight gain, as well as feed efficiency, protein conversion efficiency, and hepatosomatic index, while HSB and red drum exhibited limited responses in these growth parameters. Alternatively, only juvenile red drum showed significantly (P<0.05) increased muscle yield ratios with increasing dietary PHB while whole-body proximate composition analyses revealed no significant (P>0.05) differences in any feeding trial. Thus, a species-specific effect of PHB was observed for growth parameters, condition factors, and immunological responses of Nile tilapia, HSB, and red drum juveniles, with Nile tilapia exhibiting the most dramatic, positive responses. | |
