Growth, immunological and physiological parameters of white shrimp Litopenaeus vannamei reared at different salinity levels (1, 10, 15, 25 and 35 g/L) at stocking density of 214 shrimp/m 3 were examined at 1, 30 and 63 days. Results showed that the total haemocyte count (THC) of shrimp decreased with time at all salinity levels, indicating a potential reduction in the resistance of shrimp against pathogens, since a low value of THC indicates a perturbation of the immune system. Glucose and protein values observed in the haemolymph throughout the study indicate that shrimp adapted well to low salinities (1, 10 and 15 g/L). Although of those shrimp reared at 10 g/L only 83.3% survived, at this salinity, shrimp depicted a higher glucose concentration in haemolymph at the beginning and end of the study. K E Y W O R D Simmune and physiological response, Litopenaeus vannamei, salinity

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We evaluated the inhibition activity of extracts from two common plants, moringa (Moringa oleifera) and croton (Croton californicus), against Vibrio parahaemolyticus (IPNGS16), which causes acute hepatopancreatic necrosis disease (AHPND). The experiment was developed in three phases. First, extracts were prepared, and phytochemical screening of plants was performed. Second, microbiological tests were applied to calculate the minimum inhibitory concentration (MIC). Finally, two bioassays were performed on juvenile shrimp by administering the extracts (first) in shrimp feed at 24 and 72 h, pre-infection, and the second in feed and directly to the culture water. Based on preliminary results of antimicrobial activity, an extract concentration of 60 mg mL-1 inhibited V. parahaemolyticus (IPNGS16) at a final concentration of approximately 1×106 CFU mL-1. Bioassays were carried out in order to determine the V. parahaemolyticus (IPNGS16) median lethal dose (LC50) for juvenile Penaeus vannamei (0.20 ± 0.05 g); the LC50 was 85×103 CFU mL-1. As a first test, the extracts were added to commercial feed at doses of 20, 40, and 60 mg mL-1. After feeding, the shrimp were infected with V. parahaemolyticus (IPNGS16), and mortality was recorded. For the first infection time (24 h), survival was 46 and 33% with croton and moringa, respectively; for the second infection time (72 h), survival was 16 and 25% with croton and moringa. Application of antibacterial extracts directly to culture water were effective against V. parahaemolyticus (IPNGS16). The best result (94% survival) was obtained with a high dose (3.6 mg mL-1 or 30%) of moringa extracts added directly to culture water. Moringa methanol extracts produce active compounds capable of inhibiting replication of V. parahaemolyticus (IPNGS16) in shrimp aquaculture and reducing shrimp mortality.