To explore the impact of sedimentary nitrogen and phosphorus on Cladophora occurrence, we conducted a microecosystem experiment simulating different nitrogen and phosphorus content as well as nitrogen-to-phosphorus ratios in the sediment. Subsequently, to further explore the specific mechanism of influence that epiphytic algae have on Cladophora, we designed various microsystem culture experiments. These results revealed that an N/P ratio of 40:1 was relatively unfavorable for Cladophora growth. Additionally, there was an extremely significant negative correlation between the benthic cyanobacteria coverage on the sediment surface and the wet weight of Cladophora (p < 0.01), indicating that benthic cyanobacteria could inhibit the growth of Cladophora. Total nitrogen levels in the water column showed a significant positive correlation with phytoplankton biomass (p < 0.05), while benthic cyanobacteria coverage exhibited an extremely significant positive correlation with phytoplankton biomass through phosphorus absorption and nitrogen release (p < 0.01). Metabolite analysis of benthic cyanobacteria identified annotations for 313 metabolites; among them cis,cis-muconic acid (32.48‰), erucamide (9.52‰), phosphoric acid (6.97‰), fenpropidin (6.53‰), and propionic acid (5.16‰) accounted for proportions exceeding 5‰. However, none of these metabolites have been recognized as allelochemicals or toxins at present. This study provides novel insights into controlling Cladophora occurrence by considering sediment nutrients, including nitrogen and phosphorus, along with allelochemicals.

The fermentation product FP-WeiGuangSu is regarded as a novel, green and efficient antibiotic substitute. Such products constitute one of the principal strategies for addressing bacterial diseases in aquaculture in the future. This study investigates the effects of FPs derived from Bacillus subtilis on the antioxidant capacity and gut microbiota of Largemouth Bass (Micropterus salmoides). Experimental diets containing 0, 1%, 3% and 5% FPs (Control, H1, H2 and H3) were fed to M. salmoides. Although short-term administration of FPs exerted no significant influence on the growth performance of Largemouth Bass, serological findings demonstrated that supplementation with FPs decreased the contents of the liver injury markers ALT, AST and AKP, along with liver MDA content, and enhanced antioxidant capacity (SOD, CAT and GSH-px). Notably, the addition of 1% FPs significantly improved the systemic antioxidant performance (SOD, CAT, GSH-px and T-AOC). Moreover, the FP supplementation increased the expression levels of il-10 and IgM, and lipolysis-related genes. The results of gut microbiota analysis revealed that FPs significantly altered the diversity and structure of gut microbiota. The LEfSe results indicated that the microbial marker of the control group was Cetobacterium, those of the H1 group were Bacillus and Mycoplasma, those of the H2 group were Acinetobacter, Paenibacillus and g_unclassified_Rhizobiaceae, and that of the H3 group was Enterococcus. The most significant microbial marker upon the addition of FPs was Paenibacillus, and the pathways for biosynthesis of secondary metabolites, biosynthesis of antibiotics, and biosynthesis of amino acids were significantly activated. The Bugbase analysis results suggested that, compared with the control group, the abundance of anaerobic bacteria in the FP group decreased, while the abundance of microorganisms with mobile-element-containing and oxidative-stress-tolerant phenotypes increased. Hence, this study demonstrated that 1–3% FP dietary supplementation can be used to enhance antioxidant ability, and liver and intestine health of M. salmoides in the aquaculture industry and can be regarded as a promising feed additive in aquaculture.