Andrographolide loaded Pickering emulsion: A bioactive component for improved growth, digestibility, and haematological properties in cultured common carp Cyprinus carpio

In aquaculture, the therapeutic potential of andrographolide had been beneficially documented but still restricted owing to its high dosage and low bioavailability. To maximize andrographolide's potential value in carps, we want to create an effective delivery mechanism. During the 8-week Cyprinus carpio feeding trial, we aimed to test a low dose (0.05 g kg−1 or 0.005%) andrographolide-supplemented diet with or without a novel delivery system (chitosan particles stabilized Pickering emulsion). The experiment included four treatment groups, having a commercial carp feed as basal diet (control), diet containing Pickering emulsion without andrographolide encapsulation (PE), diet with free andrographolide (without Pickering emulsion) (AGL), diet with andrographolide encapsulated Pickering emulsion (AGL-PE). A significantly improved (p < 0.05) body weight, thermal growth coefficient and feed conversion ratio of the AGL-PE group was observed than control or AGL alone. It demonstrated improvement of AGL's efficacy may be brought by a proper delivery system. However, the delivery system alone (PE) did not significantly interfere with the results, as the differences of PE group were non-significant (p > 0.05) with either control or AGL group. The apparent digestibility coefficient of dietary nutrients, most notably protein, fiber, carbohydrates, and energy, had improved significantly (p < 0.05) by AGL-PE treatment compared to control. This most likely resulted in improved feed utilization and growth. AGL-PE addition in carp feed did not alter the ionic concentration of common blood electrolytes or metabolites, with the exception of nitrogen factors such as NH3, urea, and creatinine, possibly because of a higher digestible intake of nitrogen. Haemato-biological parameters showed a significant increase in lymphocyte, albumin, globulin, total protein, triacylglycerol with AGL-PE group (p > 0.05) than control supporting a stress free and strengthened immune system. Additionally, AGL-PE significantly improved survivability of common carp when challenged with koi herpes virus (KHV) due to immunostimulant effect of andrographolide (and chitosan in PE). Neutrophil left shift, a marker we used for establishing immunostimulant effect, was persistently high when either PE or andrographolide was introduced in diet; even maximum when they formed a hurdle system in AGL-PE diet. Modulation of Neutrophil left shift was possibly associated with amplified gut microbiota activity that coincided with higher fiber (and NFE) digestibility of AGL-PE group. The results firmly establish application of AGL-PE system as prebiotic additive in commercial aquafeed to simultaneously improve digestibility, feed utilization, growth, immunomodulatory and haematological properties in cultured fish.