Effect of the bipolar aluminum electrocoagulation model (BAEM) on heavy metal concentration, growth, immunological response, and parasitic activity in cultured Dicentrarchus labrax in underground seawater

This study assessed the effectiveness of the bipolar aluminum electrocoagulation model (BAEM) as a water treatment method for heavy metal pollution and parasitic load in Dicentrarchus labrax. Over a six-month experiment, the growth and health of D. labrax fingerlings were monitored under two BAEM treatment schedules: T2 (8-h daytime) and T3 (4-h daytime and 4-h night). Basic water physicochemical parameters were analyzed, and ectoparasites' prevalence, infection intensity, and mortality rate were investigated. Additionally, the growth performance and immune response of the BAEM-treated fish were compared to those of the control nontreated T1 fish. Parasitological examination of fresh skin and gill mounts revealed three common ectoparasites: the protozoan Trichodina sp., the monogenean Diplectanum sp., and the digenean Transversotrema sp. The results demonstrated significant improvements in water quality, with reduced turbidity, total dissolved solids, and heavy metal concentrations. The highest reduction percentages for the heavy metals iron, copper, zinc, and lead were observed in the BAEM-treated samples at T3. Additionally, the BAEM-treated groups exhibited lower prevalence and infection intensities of ectoparasites and enhanced growth performance and immune responses compared to the control group T1. This study presents the first evidence of the BAEM model's effectiveness in enhancing physicochemical parameters, reducing ectoparasite prevalence, and improving growth and immunological responses in cultured fish reared in untreated underground seawater. The model's positive outcomes make it recommended for RAS aquaculture systems and areas with high heavy metal concentrations.