Effect of autochthonous live yeasts on survival, growth, digestive functionality, and innate immune response in cobia (Rachycentron canadum) larvae

The use of host-derived probiotic yeasts is a promising strategy to enhance larval performance, but their effects during and after supplementation remain poorly understood. This study evaluated the effects of three autochthonous yeast strains: Candida haemuloni C27, Debaryomyces hansenii C10, and D. hansenii C28, isolated from cobia ( Rachycentron canadum ). A well-known strain, D. hansenii CBS8339 (isolated from rainbow trout), was included for comparison. Larvae were fed for 14 days (2–15 days post-hatch, dph) with rotifers and Artemia metanauplii enriched with each yeast strain. A total of 75,000 larvae (2 dph; ∼3 mm) were randomly distributed into 15 tanks, with three replicates assigned to each of five groups: three groups received yeasts, one group was supplemented with D. hansenii CBS8339, and one control group received non-enriched live food. Digestive enzyme activity, larval growth, and yeast persistence in the gastrointestinal tract were assessed during (6 and 12 dph) and after (18 and 24 dph) supplementation. Survival and innate immune gene expression were evaluated at 24 dph. The results showed that all strains except D. hansenii C10 remained viable in the larval gut until 24 dph. Larvae fed C. haemuloni C27 and D. hansenii CBS8339 showed higher acid protease activity during supplementation. After supplementation, D. hansenii C28 enhanced the activity of eight out of nine digestive enzymes analyzed, while all yeast-fed groups showed increased α-amylase and lipase activity. C. haemuloni C27 upregulated il-1β and tnf-α expression. Survival was improved in larvae supplemented with C. haemuloni C27 and D. hansenii C28 (∼31 %) compared to the control (∼22 %). No differences in growth or intestinal histology were detected between treatments. These findings demonstrate that C. haemuloni C27 and D. hansenii C28 exert beneficial effects in cobia larvae by enhancing survival, digestive function, and immune response with lasting effects likely due to their persistence in the gut. • Viable yeasts were detected in larvae during and after supplementation. • Probiotic effects persisted beyond the supplementation period. • C. haemuloni C27 and D. hansenii C28 enhanced larval survival in cobia. • C. haemuloni C27 upregulated innate immune cytokine expression. • D. hansenii C28 enhanced the activity of most digestive enzymes.