The increasing need for healthy protein to feed the growing global population has led to rapid expansion in shrimp production (Litopenaeus vannamei), however, increasing disease problems have occurred. Oregano essential oil (OEO) has been widely demonstrated to support the health and performance of monogastric livestock, however, to date little research has been performed in aquatic species. To investigate the effect of OEO in shrimp a trial was performed at Nong Lam University in Vietnam under Vibrio parahaemolyticus challenge.
Pathogen-free shrimp from post-larval stage were raised for 8 weeks in a recirculation system using two treatments (Control and OEO). Shrimp were fed 4 times daily at 5% of mean body weight and uneaten food was removed after 2 hours and dried then deducted from the total feed. Water temperature was 27± 1o C and salinity was 10 ± 5 g l-1. Water changes and bio-filtration kept ammonia below 0.5mg l–1 and nitrite-N below 0.15 mg l–1. Shrimp with initial weights of 1.5±0.2g were randomly assigned to 0.5m3 tanks with four tanks per treatment. Basal diets are shown in (Table 1). Orego-Stim Forte (Anpario plc.) was added to one treatment at 3.5kg/t. At 8 weeks, 20 shrimp per treatment were challenged with Vibrio parahaemolyticus at 105 CFU/ml (confirmed via spectrophotometry and serial plate counts) and mortality was assessed over 14 days. Data was statistically analysed in IBM SPSS 2.0 using one-way ANOVA with a Duncan posthoc.
There was no significant difference in growth performance between treatments (Table 2). However, following the bacterial challenge, there was a significant 17.5% reduction in total mortality (p<0.05) at the end of study between the Control and OEO groups (Figure 1).
Conclusion: The dietary supplementation of OEO resulted in a significant reduction in total mortality under Vibrio parahaemolyticus challenge. This suggests that OEO could be a useful tool for controlling bacterial challenge in shrimp.