Toxicodynamic effects of chronic Pb2+ exposure on milkfish (Chanos chanos) and the phytoremediation role of Caulerpa Taxifolia: Water quality, bioaccumulation, and multi-level biological responses

This study investigated the phytoremediation efficacy of Caulerpa taxifolia in alleviating chronic lead (Pb 2+ ) toxicity in milkfish ( Chanos chanos ) through hematological, oxidative, histological, and respiratory indicators. Fish were exposed to 5.33 mg/L Pb 2+ for 14 days in rearing systems integrated with Caulerpa taxifolia biomass at 25, 50, 75, and 100 g. The macroalga demonstrated strong biosorption capacity, with Pb 2+ accumulation reaching 1.23 ± 0.23 mg/g at 100 g dosage. Liver tissue from fish in phytoremediated systems exhibited reduced degeneration and necrosis. Hematological profiles improved significantly; RBC counts increased from 1.68 × 10 6 to 2.18 × 10 6 cells/mm 3 , and hemoglobin rose from 7.22 to 9.10 g/dL. Oxidative stress was mitigated, as indicated by lower SOD and CAT activities, reduced MDA levels, and attenuated GST activity in phytoremediated groups. Erythrocyte malformations were also reduced. Respiratory parameters, including opercular beat and oxygen consumption rates, remained more stable in Caulerpa taxifolia integrated systems. Survival rates improved from 60 % in the Pb 2+ only group to 90 % in the 75–100 g groups. Bioactive profiling of Caulerpa taxifolia revealed increased levels of phenolics, flavonoids, and carotenoids under Pb 2+ stress. These findings highlight Caulerpa taxifolia as an effective phytoremediator, functioning both as a biofilter that reduces dissolved Pb 2+ concentrations and as a source of antioxidant compounds that help mitigate oxidative stress, improve hematological parameters, and promote recovery from histopathological alterations in fish tissues. • Caulerpa taxifolia lowered Pb 2+ in water and bioaccumulated it in tissues. • Hematological and oxidative stress responses improved under phytoremediation. • Liver pathology and erythrocyte malformations decreased with higher biomass. • Fish survival improved from 60 % to 90 % with 75–100 g Caulerpa taxifolia .