Aims: The activity of two essential oils (EOs) of Cinnamosma fragrans, an endemic plant to Madagascar (B8: linalool-type and B143: 1,8-cineole-type), against bacterial isolates from a shrimp hatchery of Penaeus monodon and their effects on the survival and bacterial concentration of larvae were determined. Methods and Results: Minimum inhibitory concentrations were determined using a broth dilution technique. The bacterial concentrations of both larvae and water tank were assessed on Marine agar and Thiosulfate Citrate Bile Sucrose agar. The assays took place in OSO Farming's shrimp hatchery in Madagascar. EOs were directly added to the water tank. Regarding the survival, the assays in larval culture (four replicates each of B8, B143, E and control) showed that B8 oil had a similar effect (P > 0Æ05) as the antibiotic (Erythromycin) and was more active than B143 (P < 0Æ05). A negative correlation was observed between the bacterial concentration and the survival of larvae for all assays. Conclusion: Both C. fragrans essential oils, as antibiotic, exhibited significantly higher survival rates and lower bacterial concentrations of the larvae than the control (oil and antibiotic free). Significance and impacts of the study: The potential of C. fragrans essential oil to control the bacterial load in in vivo conditions, thereby enhancing survival rate of P. monodon larvae, makes it a relevant option for developing a novel alternative to antibiotics in shrimp hatchery culture.