Effects of Orange Peel-Derived Carbon Sources on Nannochloropsis salina Mixotrophic Cultivation

Plant-Derived Aqueous Extracts as Bio-Based Modulators of Dunaliella salina Growth for Sustainable Cultivation

This study assessed the effects of aqueous extracts from turmeric (Curcuma longa), mint (Mentha sp.), grape peel (Vitis sp.), and mango peel (Mangifera indica) on the growth and total carotenoid content of the microalga Dunaliella salina. A two-stage cultivation strategy was employed, in which aqueous extracts prepared by decoction were added at 0.5% (v/v) either at the inoculation or after the exponential growth phase. Microalgal growth was monitored by direct cell counting, and total carotenoid content was determined spectrophotometrically in the harvested biomass. The chemical profiles of the extracts were characterised by HPLC-MS/MS, enabling the annotation of key phenolic and flavonoid compounds. Specific orange turmeric and mint formulations enhanced microalgal cell proliferation by up to 31.88% and 28.95%, respectively, compared to the control. However, despite the higher biomass, the total carotenoid content did not increase correspondingly; orange turmeric extract even led to reductions of 90.84 to 92.86% in carotenoid content. These findings suggest that exogenous antioxidants may suppress the oxidative stress signals required to trigger carotenoid biosynthesis in D. salina. Additionally, grape peel extracts prepared at higher temperatures promoted better algal growth than those obtained at lower temperatures. These findings highlight the dual role of plant extracts in modulating microalgal growth and secondary metabolism, demonstrating that antioxidant-rich extracts may be used to enhance biomass accumulation before the subsequent induction of stress-mediated carotenogenesis, thereby potentially improving biotechnological yields.

Effects of Three Dried Citrus Peels as Feed Additives on Growth Performance and Intestinal Microbiota of Oreochromis niloticus

Citrus processing generates large quantities of peel by‐products that are often discarded, resulting in resource waste and environmental burden. This study systematically evaluated the effects of dietary supplementation with fresh Citrus reticulata “Gonggan” peel (NG), fresh C. reticulata “Chachi” peel (NC), and 3‐year‐aged C. reticulata “Chachi” peel (3 C) on growth performance, muscle quality, antioxidant capacity, immune response, and intestinal microbiota of Oreochromis niloticus. Fresh peels, particularly NG, contained higher concentrations of total flavonoids than aged peels. All three peel additives tended to improve growth performance, with 3C showing the most pronounced growth‐promoting effect. Dietary supplementation significantly increased the levels of sweet‐ and umami‐associated amino acids in muscle. The NG group exhibited the highest antioxidant enzyme activities and inflammatory/stress‐related marker expression levels, whereas the 3C group showed the lowest levels of oxidative and inflammatory markers. Intestinal microbiota analysis revealed increased microbial richness and altered community composition in all treatment groups, with 3C notably enhancing microbial diversity and altering taxa abundance patterns. Collectively, these findings suggest that three distinct citrus peels may exert differential functional effects as feed additives, although inclusion level and peel type influence the balance between growth promotion and immune activation. This study provides preliminary evidence supporting the utilization of citrus by‐products in aquafeeds and supports sustainable and circular aquaculture development.

Potencial biotecnológico de las microalgas como biofertilizantes para mitigar el estrés salino en cultivos

The collected evidence shows that genera such as Chlorella, Scenedesmus, Dunaliella, Arthrospira, and several cyanobacteria improve nutritional efficiency, increase antioxidant activity, promote ionic balance, and reduce oxidative damage induced by excess salts.

Deciphering the phyto-immunomodulatory potential of orange (Citrus sinensis) peel in goldfish (Carassius auratus) diet against Aeromonas hydrophila

The increasing demand for sustainable and functional feed additives in aquaculture has driven interest in agro-industrial by-products such as orange (Citrus sinensis) peel, which are rich in bioactive compounds. This study investigated the effects of dietary orange peel supplementation on growth performance, digestibility, physiological responses, and disease resistance in goldfish Carassius auratus. Fish were fed diets containing 0% (control), 2.5%, 5%, and 7.5% orange peel for 60 days, followed by analyses of growth, digestive enzymes, haematological, biochemical, immunological parameters, and a pathogen challenge test. Results showed that the 2.5% inclusion level significantly enhanced growth, with approximately two-fold higher weight gain and improved feed conversion ratio (ANOVA: p < 0.05). Protein digestibility increased by ~20% in 2.5% and 5% groups, while digestive enzyme activities, particularly amylase (~120% increase) and protease (~25% increase), were markedly elevated. Haematological indices (RBC, HB, HT) improved significantly (p < 0.001), while glucose, triglycerides, and cholesterol were reduced in higher inclusion groups (p < 0.001). Antioxidant (SOD, CAT) and immune responses (NBT, MPO) were significantly enhanced (p < 0.001), indicating improved oxidative stress resistance and immune competence. Carotenoid deposition increased significantly in muscle (~24%) and skin (~23%). Following Aeromonas hydrophila challenge, survival improved up to 1.7-fold in supplemented groups (p < 0.05). Overall, the results demonstrate that orange peel, particularly at 2.5% inclusion, serves as an effective, sustainable functional feed additive that enhances growth, physiological health, and disease resistance, offering practical implications for improving aquaculture productivity and resilience.

Valorisation of Citrus paradisi peel wastes to pharmacologically active essential oil: GC–MS analysis and pharmacological screening

Lipid fluorescence and antioxidant activity in microalgae under polystyrene microplastic stress

Microplastic (MP) pollution, particularly polystyrene (PS), poses a growing threat to aquatic ecosystems and primary producers such as microalgae. Three mangrove-derived diatoms, Nitzschia navis-varingica , Nitzschia palea , and Navicula bory , were used in this work to assess the effects of 2 μm PS MPs on lipid content and antioxidant activity. Clonal cultures were subjected to PS doses of 0, 5, 10, and 50 mg/L. Nile Red fluorescence staining and corrected total cell fluorescence (CTCF) were used to measure lipid content, while IC 50 values from the DPPH experiment were used to measure antioxidant activity. In all species, the exposure to PS initially decreased lipid fluorescence, especially at 50 mg/L, suggesting transient metabolic stress. Nevertheless, species-specific adapta - tion responses were noted, with lipid accumulation rising during cultivation and peaking on day 1 in N. bory and day 9 in both Nitzschia species. While N. navis-varingica did not exhibit any significant variations between treat - ments, N. palea and N. bory revealed significant effects of PS on lipid content (p<0.05). Significantly reduced IC 50 values in all species (p<0.05) indicate that antioxidant activity increased along with PS concentration, with the highest activity seen at 50 mg/L. These findings demonstrate that PS promote oxidative stress and affect lipid metabolism in mangrove microalgae, while also eliciting adaptive antioxidant responses. The observed species-specific reactions point to possible ecological repercussions for trophic interactions and primary productivity in aquatic environments polluted by MPs.