Modulatory effects of plant extract combinations on growth performance, hepato-intestinal homeostasis, intestinal microbiota, and Streptococcus agalactiae resistance in Acrossocheilus fasciatus

This study aimed to evaluate the effects of a composite herbal extract (CSPS), formulated with Caesalpinia sappan, Schisandra chinensis, Prunus mume, and Syzygium aromaticum at an optimized ratio of 2.96:3.00:1.11:1.04, on the growth performance, hepato-intestinal homeostasis, intestinal microbiota, and anti-Streptococcus agalactiae resistance of Acrossocheilus fasciatus. In vitro antibacterial assays showed CSPS exhibited a 29.70 mm inhibition zone and a minimum inhibitory concentration of 31.25 mg·mL⁻¹ against Streptococcus agalactiae strain ZSTU01. A two-phase feeding trial was conducted: Phase I (28 days) identified 0.5 g·kg⁻¹ feed as the optimal CSPS dose, yielding the highest survival rate (70.0%) post-S. agalactiae challenge (LD₅₀ = 6.88 × 10⁶ CFU·g⁻¹). Phase II (28 days) confirmed this dose had no adverse effects on growth performance or feed utilization but significantly improved hepato-intestinal health: it reduced hepatocyte vacuolation, increased intestinal villus height, modulated hepatic enzyme activities (decreased AST and AKP, increased ACP), and reshaped the intestinal microbiota. Specifically, CSPS supplementation elevated beneficial bacteria (Cetobacterium somerae, Cloacibacterium) and reduced pathogenic taxa (Aeromonas veronii, Neochlamydia), without altering microbial α‑diversity. These changes enhanced non-specific immunity and intestinal health, contributing to improved resistance against S. agalactiae. Collectively, dietary CSPS at 0.5 g·kg⁻¹ is a potential antibiotic alternative candidate for A. fasciatus aquaculture, exerting protective effects via gut microbiota modulation and physiological homeostasis regulation.