Vibrio parahaemolyticus commonly found in coastal areas and estuaries. It causes acute hepatopancreatic necrosis disease (AHPND), a condition previously known as early death syndrome (EMS). Phytogenics has been widely used in aquaculture because of their antibacterial activity and less pollution. The feeding and disease challenge trial was conducted to evaluate the impact and efficacy of a natural feed additive on the growth and health of Litopenaeus vannamei.
Four treatment groups were designed, among which, the control group was standard feed; the trial group 1 (T1) was standard feed with 0.2% natural feed additive; the trial group 2 (T2) was standard feed with 0.4% natural feed additive; the negative control group (NC) was standard feed with 0.0015% florfenicol which purity is above 98%. First, 360 shrimps with body weight of (2.30±0.07)g were randomly divided into 12 buckets with 3 replicates in each treatment group and 30 shrimps in each replicate. During the trial, the water was natural seawater after gauze filtration and disinfection, and the water temperature was 29~31℃. The water was changed 4/5 per day, the feed was 4 times per day, the daily feed was 5% ~ 7% of the shrimp body weight. After 52 days of the feeding trial, the remaining shrimp after sampling were challenged with Vibrio parahaemolute at 108CFU/ml. Mortality was then monitored for 72 hours.
As can be seen from Table 1, there was no significant difference in survival rate between all treatment groups. The final weight, weight gain rate and specific growth rate showed a similar trend, and the T2 group was significantly higher than that of control group and NC group (P<0.05). According to the results of challenge test in table 2, shrimp in T1 and T2 groups had lower mortality than the control group and NC group after 72 hours.