<![CDATA[Graphical Abstract Highlight Research Potential probiotic yeast non-Saccharomyces for the aquaculture sector has been explored. To the best of our knowledge, this is the first study to evaluate the potential of ohmeri as a candidate probiotic yeast in whiteleg shrimp under V. parahaemolyticus challenge. Effect of yeasts ohmeri and C. parapsilosis as growth promoters and immunostimulants against V. parahaemolyticus infection in whiteleg shrimp has been revealed. K. ohmeri and C. parapsilosis improved growth performance and influenced hemocyte-related immune parameters in whiteleg shrimp following V. parahaemolyticus challenge. Abstract Bacterial disease constrains shrimp aquaculture, motivating non-antibiotic approaches to improve growth and survival. However, the performance of non-Saccharomyces yeasts in whiteleg shrimp remains poorly characterized. This study compared the candidate probiotic yeasts Kodamaea ohmeri GU12 and Candida parapsilosis GU13 for growth, microbial abundance, hemocyte responses, and survival following Vibrio parahaemolyticus challenge in Litopenaeus vannamei. A completely randomized aquarium experiment allocated 240 shrimp among four treatments: the two yeast candidates, a challenged positive control, and an unchallenged negative control. Three independent aquaria per treatment were retained for analysis. The aquarium, rather than each individual shrimp, was treated as the independent experimental replicate unit. Yeasts were administered through rearing water for 30 days, followed by bacterial challenge on day 31 and seven days of monitoring. Kodamaea ohmeri yielded a specific growth rate of 4.00 ± 0.29% day⁻¹ and feed conversion ratio of 1.46 ± 0.23, outperforming controls in growth-related measures. Both yeast treatments showed lower total Vibrio and V. parahaemolyticus counts than the positive control, alongside differences in total and differential hemocyte profiles. Following challenge, survival reached 82.8% with K. ohmeri and 74.8% with C. parapsilosis, compared with 52.9% in the positive control; the unchallenged negative control reached 95.7%. Together, these findings suggest that the candidate yeasts, particularly K. ohmeri, were associated with improved growth-related performance and post-challenge survival under the tested aquarium conditions. Because these yeasts have potential safety concerns and experimental findings may not generalize to farms, strain-specific safety assessment, mechanistic investigation, and field-scale validation are needed before practical application.]]>
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