Effects of dietary microalgae supplementation at different levels on Macrobrachium rosenbergii insect meal-based diets: Antioxidant capacity, hepatopancreatic morphology, and carotenoid retention

The replacement of fish meal with insect meal (IM) in aquafeeds is increasingly promoted as a sustainable strategy to reduce dependence on marine resources. However, IM based diets are inherently low in carotenoids and natural antioxidants, which can limit pigmentation, oxidative stability, and final product quality in crustaceans. Although IM inclusion in shrimp diets has been widely reported, to our knowledge, no study has evaluated whether supplementation with bioactive ingredients can functionally enhance IM based diets. This study investigated whether carotenoid-rich microalgae could compensate for these limitations in black soldier fly meal-based diets for the giant freshwater prawn (Macrobrachium rosenbergii). Experimental diets were supplemented with 2.5 % or 5 % Arthrospira platensis (Spirulina) or Haematococcus pluvialis and evaluated during a 60-day nursery trial. Growth performance, carotenoid retention, colorimetric traits, antioxidant status, lipid peroxidation, and hepatopancreas histology were assessed. Growth performance did not differ among treatments (P > 0.05). In contrast, microalgae supplementation significantly increased astaxanthin, lutein, and β-carotene retention, confirming that IM alone does not adequately support pigmentation-related quality traits. The highest total carotenoid concentration was observed in prawns fed the H5 diet (35.4 μg g⁻¹). Spirulina primarily enhanced raw prawn coloration, whereas H. pluvialis significantly affected cooked prawn color. Antioxidant capacity was highest and lipid peroxidation lowest in the S2 treatment, while higher inclusion levels (5 %) were associated with elevated oxidative stress. These findings demonstrate IM capabilities can be effectively enhanced through moderate microalgae supplementation. Inclusion at 2.5 % optimised coloration, carotenoid retention, and antioxidant status, without compromising growth, supporting the development of high-quality, sustainable insect-based prawn diets.