International Journal of Aquaculture, 2025, Vol.15, No.1, 11-20 http://www.aquapublisher.com/index.php/ija 17 range from phenolic acids, such as protocatechuic, p-hydroxybenzoic, vanillic, syringic, and ferulic acids, to flavonoids, including catechin, quercetin, homoorientin, orientin, taxifolin, deoxyhexose, isovitexin, and scopoletin. Figure 3 Open arrows show cytoplasmic vacuolization in the liver tissue of koi carp at 0.0% CD (A); asterisks show necrotic tissue in the liver of koi carp at 0.0% CD (B); Tukey (p<0.05) In simplified terms, diets supplemented with açaí, due to the higher concentration of phytochemicals, contribute to the high antioxidant capacity observed in this study. According to Abbate et al. (2021) and Akbari et al. (2022), phenolic compounds and polyphenols, such as flavonoids, are effective in combating oxidative stress, promoting cell health, and increasing resistance to diseases and stress. The antioxidant process possibly involved is the neutralization of reactive molecules by non-enzymatic substances. Li et al. (2022) describe that these substances play an important role in reducing the activity of free radicals, leading to a decrease in the chain reactions mediated by these radicals and, consequently, protecting cells from oxidative damage. Among the non-enzymatic molecules present in açaí, flavonoids stand out, which may be associated with this antioxidant action, as evidenced by Rudenko et al. (2023) and Hu et al. (2025). The research by Carvalho et al. (2017) on the antioxidant capacity of genotypes of Euterpe oleracea pulp supports the results of this study, as it showed that açaí pulp exhibited high values in 2,2-diphenyl-1-picrylhydrazyl (DPPH) tests, as well as an increase in Oxygen Radical Absorbance Capacity (ORAC) and Trolox Equivalent Antioxidant Capacity (TEAC), confirming the exceptional effectiveness of açaí pulp in eliminating free radicals. The results obtained indicated attenuated histological changes as the inclusion of açaí in the fish diet increased. The hepatic tissue plays a key role in the metabolism process, including nutrient absorption and detoxification (Popović et al., 2023). Therefore, monitoring this tissue is crucial for assessing the animals' health status. The loss of the cord-like structure was more intense in the control group, possibly related to the larger area of necrotic tissue, which was also more pronounced in this group. As a result, tissue degeneration hindered the formation and organization of the sinusoidal cords. These findings suggest that açaí supplementation exerts a protective action against hepatic tissue degeneration, possibly due to its antioxidant and anti-inflammatory compounds. The high antioxidant capacity of açaí neutralizes free radicals and reduces oxidative stress in hepatic tissues, as observed by Laurindo et al. (2023), which likely contributed to a hepatoprotective effect in the supplemented animals. These results are significant as they support observations made by Colombo et al. (2020), who identified antioxidant and hepatoprotective effects in Litopenaeus vannamei after the inclusion of açaí (10%) in the diet, and by Moura et al. (2022), who obtained promising results regarding the inclusion of açaí in the diet on mortality rates and batch uniformity, at concentrations of 2.48% for Pterophyllum scalare and 0.88% for Heros severus. However, in the group that received 2.0% açaí in the diet, the highest index of sinusoidal congestion was observed compared to the other treatments. This condition may be associated with an increase in blood flow to the liver or a reduction in the organ’s ability to adequately drain blood, potentially affecting liver function and leading to more severe complications (Téllez et al., 2022). According to Pereira et al. (2016), an increase in sinusoidal congestion was also observed in rats fed fat-rich diets supplemented with açaí. Furthermore, the congestion observed may
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