Synergistic effects of the β-1,3 glucan paramylon and vitamin C on immunological responses of hybrid striped bass (Morone chrysops × M. saxatilis) were pronounced in vitro but more moderate in vivo.

Abstract

The objective of this study was to evaluate if immunostimulation by the β-1,3-glucan paramylon (PML) could be further enhanced with vitamin C (vit. C) for hybrid striped bass (HSB). Two separate trials were conducted in vitro and in vivo, using a 2 × 2 factorial design, where the main effects tested were PML and vit. C, or their combination (PML + vit. C), to measure possible synergistic effects on various immunological responses. Supplementation of PML in vitro to whole-blood significantly (P < .001) increased the plasma lysozyme activity, and vit. C increased the concentration of total protein (P < .01) and immunoglobulins (P < .001) in the plasma. Synergistic effects (P < .0001) were observed for the production of reactive oxygen species in whole-blood and isolated phagocytes. After corroborating the interaction of PML and vit. C in vitro, a feeding trial was conducted using HSB juveniles (~9.30 g initial weight). Fish were fed diets with 100 mg of PML kg−1, 500 mg of vit. C kg−1 or their combination (100 mg of PML + 500 mg of vit. C kg−1). A basal diet with no supplementation served as the control. Fish were fed for 8 weeks after which production parameters were recorded, and proximate composition of whole-body tissues, immunological components of the blood and plasma, phagocytes isolated from the head kidney, and enzyme activities in intestinal sections were analyzed. Supplementation of PML slightly impaired HSB growth performance and feed efficiency, and decreased the moisture content of whole-body tissues when compared to the non-supplemented group. However, fish fed diets supplemented with PML presented higher concentrations of plasma immunoglobulins, intracellular superoxide anion production, acid phosphatase activity in the posterior part of the intestine, and lysozyme activity in the anterior part of the intestine. A synergistic effect between PML and vit. C for acid phosphatase activity was observed in the anterior part of the intestine, and for whole-blood respiratory burst. Therefore, based on the results from both trials, synergism between PML and vit. C was most pronounced in vitro in terms of reactive oxygen species production, and limited enhancement of immunological responses were observed in vivo after the feeding trial.