Effects of dietary supplementation with astragalus (Astragalus membranaceus) root or leaf meal on the hematology, serum biochemical parameters, histomorphology, oxidative status, and resistance of Phoxinus lagowskii against bacterial infection

The present study sought to investigate the effects of Astragalus membranaceus root (AMR) and A. membranaceus leaves (AML) on the growth performance, immune and antioxidant response, and disease resistance of Amur minnow (Phoxinus lagowskii). Here, we compared the health-promoting effects of AMR- and AML-supplemented diets on P. lagowskii and assessed whether the AML could be used as a candidate dietary supplement to promote fish health. After 8 weeks of feeding, the AM-supplemented groups exhibited higher growth performance, especially the AMR 0.5% and AML 1.0% groups. Hematological parameters including white blood cells (WBC), red blood cells (RBC), and mean cell volume (MCV) were significantly increased in fish fed supplementation with AM-containing diets compared to the basal diet, and the WBC was highest in the AML 1.0% group. The highest serum lysozyme level was found in fish fed with a diet containing 0.5% AMR. The results of lysozyme (LZM), acid phosphatase (ACP), and alkaline phosphatase (AKP) indicated that AM supplementation had no adverse effects on P. lagowskii. The liver superoxide dismutase (SOD) activity significantly increased in the AMR1.5% group, whereas catalase (CAT) activity significantly increased in all AMR and AML groups compared to the control group. Moreover, the villus height was significantly increased in the AMR 0.5% and AML 1.0% groups. After the feeding trial, the fish supplemented with 0.5% AMR exhibited the highest tumor necrosis factor alpha (TNF-α), interleukin-10 (IL-10), inducible nitric oxide synthase (iNOS), Cu/Zn superoxide dismutase (Cu/Zn-SOD), and Mn superoxide dismutase (Mn-SOD) expression levels in the muscle. Furthermore, both AMR and AML dietary supplementation enhanced the resistance of P. lagowskii against Aeromonas hydrophila except in the AML 0.5% group. The mortality rate of fish infected with Acinetobacter tjernbergiae after AMR or AML treatment was 40% to 70%, and the survival rate of the AML 1.0% group was the highest (60%). Therefore, additional studies are needed to further evaluate the applicability of Chinese herbal medicine supplementation for the prevention of diseases caused by Acinetobacter. Collectively, our analyses of hematological parameters of WBC, villus height changes, and survival rates of bacteria-infected individuals indicated that the dietary addition of AML 1.0% is an optimal dose for P. lagowskii.