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Microalgae are major antioxidant producers and feed containing these substances is known to be beneficial. Microalgae cultivation is an alternative way to produce biodiesel and, after oil extraction, residual algal biomass (RAB) is obtained. The RAB was tested as an ingredient in fish feed production and its safety evaluation is important to prevent risks to fish health. This study aim was to evaluate, through biochemical and genetic biomarkers, the safety of RAB in catfish, Rhamdia quelen, feed. Acutodesmus obliquus microalgae RAB, cultivated in Chu medium, was used in feed formulation. A standard feed without RAB (0%) was produced, and three other feeds were enriched with RAB in 1, 2, and 3% proportion. Each feed kind was given to a 15 R. quelen fingerling group for 60 days. The evaluated biochemical biomarkers were superoxide dismutase (SOD) and catalase (CAT) activities, lipid peroxidation (LPO) in the liver, and acetilcolinesterase (AChE) activity in the brain and muscles. The genetic biomarkers analyzed were halo assay in erythrocytes, comet assay in erythrocytes, liver and brain, and piscine micronucleus. The SOD activity was increased in the 3% group; CAT activity and LPO levels were not different among the groups. In the comet assay, a significant decrease in DNA damage in erythrocytes (2 and 3%) and liver tissue (3%) was observed. In the brain, DNA damage was not observed. These results corroborate that as the RAB amount increased, the organisms showed a potential antioxidant effect, as the 3% RAB feed had the best results.