Effects of mixed microalgae on larval metamorphosis of the Pacific white shrimp Penaeus vannamei: Integrated analysis of digestion, antioxidant capacity and transcriptome

High-quality initial nutrition is critical for the larval cultivation of Pacific white shrimp, Penaeus vannamei. While mixed microalgal diets are known to be superior to single-species feeds, the underlying mechanisms of different mixing ratios remain unclear. In this study, we fed P. vannamei larvae with two microalgae, Chaetoceros muelleri (CM) and Thalassiosira weissflogii (TW), at three volumetric ratios (2:1, 1:1, and 1:2) and evaluated their effects on larval development, digestive enzyme activity, antioxidant capacity, and transcriptomics. The results revealed that the mixed-algae diets (1:1 and 1:2 ratios) significantly accelerated metamorphosis and increased body length and digestive enzyme activity (P < 0.05). However, this rapid growth came at a cost: these groups exhibited significantly lower survival and increased oxidative stress, as evidenced by decreased antioxidant enzyme activity and higher malondialdehyde (MDA) levels (P < 0.05). Transcriptome analysis revealed that the mixed diets upregulated pathways related to nutrient metabolism but downregulated pathways associated with immunity and detoxification, highlighting a “growth–immunity trade-off”. In conclusion, feeding a 1:1 or 1:2 mixed diet of C. muelleri and T. weissflogii effectively promoted larval growth but induced significant physiological stress. This study provides a molecular-level understanding of this trade-off, offering a crucial theoretical basis for developing optimized and balanced feeding strategies for crustacean larviculture.