Résumé
This study aimed to investigate the potential protection conferred by the probiotic strain NC201 against biotic and abiotic stresses in Pacific blue shrimp Litopenaeus stylirostris that had received the probiotic throughout their lives. The presence of NC201 in shrimp hemolymph was investigated over the course of 24 h, before exposure to bacterial or physical stress. Results showed that NC201 had invaded the shrimp hemolymph 2 h following administration, but had completely disappeared by 48 h. NC201 identification through morphotype observation was confirmed by MALDI-TOF biotyping and results also indicated that NC201 and Pseudoalteromonas piscicida are closely related. A challenge by immersion was carried out on subadults using Vibrio nigripulchritudo at 105 CFU/ml. Cumulative mortality was two-fold lower in the treated group (24%) than in the control group (48%) at 144 h post infection. The probiotic in the shrimp hemolymph was diminished in infectious conditions compared with non-infectious ones and V. nigripulchritudo prevalence was simultaneously lower in animals treated with NC201. The relative expression of genes coding lysozyme and penaeidin 3 was evaluated 24 h post infection and their transcript numbers were found to be lower in probiotic animals than in control animals for both genes. Hyposaline stress was also used to evaluate the benefits of NC201 treatment on early juveniles and subadults. At low salinities, animals showed an increased survival rate when treated with NC201, by 10 and 17.5% at 48 h post stress, respectively. Moreover, in subadults treated with the probiotic, a better recovery of the plasmatic osmolality was observed. All these results confirm that NC201 is a good candidate probiotic for shrimp aquaculture.