IMMUNOMODULATORY EFFECTS OF LINEAR ß-1,3-GLUCAN PARAMYLON AND BRANCHED ß-1,3/1,6-GLUCAN ZYMOSAN AS FEED ADDITIVES AND AS ADJUVANTS FOR HYBRID STRIPED BASS Morone chrysops × M. saxatilis

Beta glucans are biological modifiers that can activate the animal's innate immune system, enhancing the primary defense lines prior to a pathogenic insult. The molecular structure of beta glucan can play a role triggering distinct immunological responses when interacting with different cell membrane receptors. The objective of this study was to assess the immune responses of hybrid striped bass (HSB) when exposed to Paramylon, a linear β-1,3-glucan derived from Euglena gracilis, and Zymosan a branched β-1,3/1,6-glucan derived from the traditional Saccharomyces cerevisiae. Two separate trials evaluated the efficacy of these immunostimulants when they were delivered orally as a feed additive or injected intraperitoneally (i.p.) as an adjuvant.

For the feeding trial, five diets were formulated to contain Paramylon (50 or 100 mg kg^-1), Zymosan (50 or 100 mg kg^-1) and no supplementation serving as a basal diet. Each treatment was assigned to four replicate groups of 15 juvenile HSB averaging ~15.4 g. Blood and head kidney were sampled during an intermediate sampling at week 4 and at the final sampling at week 8. The results showed that no differences were detected for oxidative radical production from whole blood, total plasma protein, lysozyme, hemolytic and antiprotease activity. However, an increased intracellular superoxide anion production of isolated phagocytes was observed when compared to the basal group (Figure 1).

A second trial was conducted by injecting i.p. a solution from each glucan source and phosphate buffered saline serving as a control. For each treatment, 10 fish (~330 g) were injected with approximately 10 mg of β-glucan kg^-1 of body weight. Seven days after the administration, blood was collected from the caudal vasculature, and immunological profiles from whole blood and plasma were assessed. All parameters were significantly affected (P>0.05) by the treatments (Table 1). The results of this study indicate that dietary and injected Paramylon and Zymosan can modulate the immunological responses of HSB in different fashions.