Bacillus supplementation boost Whiteleg Shrimp performance and resistance to osmotic shock and Vibrio parahaemolyticus
The shrimp aquaculture industry faces significant challenges due to suboptimal culture conditions and susceptibility to opportunistic pathogens like Vibrio parahaemolyticus. Given the underdeveloped immune system of shrimp, these factors can lead to high mortality rates and economic losses. Probiotics, particularly strains of Bacillus sp., are increasingly recognized for their potential to enhance shrimp health and performance. This study, led by Florian Geay, investigates the effects of dietary supplementation with Bacillus pumilus and Bacillus subtilis on the growth, osmotic stress tolerance, and resistance to Vibrio parahaemolyticus in Whiteleg shrimp (Penaeus vannamei).
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The feeding trial was conducted using post-larval shrimp (PL12) over a four-week period. Two dietary treatments were tested: a control diet and a diet supplemented with a probiotic mix of Bacillus pumilus and Bacillus subtilis at a concentration of 8.0 x 10^6 cfu/g feed. Each treatment was administered to shrimp housed in eight 400-liter tanks, stocked at a density of 1 PL per liter. Performance metrics such as final mean weight, biomass, average daily gain (ADG), feed conversion ratio (FCR), and survival rate were recorded.
Osmotic Stress Test
At the end of the feeding period, 50 shrimp from each tank were subjected to an osmotic shock, transitioning from 8 ppt to 0 ppt salinity. Mortality was recorded every 30 minutes over a seven-hour period to evaluate osmoregulation capacity. (Figure 1)
Vibrio parahaemolyticus Challenge
Following the feeding trial, 30 shrimp from each tank were exposed to Vibrio parahaemolyticus in a bath challenge. Mortality was monitored every three hours for three days to assess resistance to bacterial infection. (Figure 2)
Results
Growth Performance
Shrimp fed the probiotic-supplemented diet showed significant improvements in growth performance metrics compared to the control group. The final mean weight, biomass, and ADG were all significantly higher in the probiotic group (p<0.05), while FCR was significantly lower, indicating better feed efficiency.
Osmotic Stress Tolerance
Shrimp fed the probiotic diet exhibited enhanced tolerance to osmotic stress, with significantly lower mortality rates compared to the control group during the osmotic shock test (p<0.01) (Figure 1). This suggests a better capacity of shrimp fed with probiotics to cope with environmental stressors.
Resistance to Vibrio parahaemolyticus
The probiotic-supplemented shrimp also demonstrated increased resistance to Vibrio parahaemolyticus infection. The survival rate was significantly higher in the probiotic group compared to the control group during the bacterial challenge (p<0.01) (Figure 2). The probiotics likely contributed to this improved resistance by competing with the pathogen for nutrients and adhesion sites, and by stimulating the shrimp's immune system.
Figure 1: Mortality recorded over the osmotic stress test performed at the end of the feeding trial (N=400)
The results of this study underscore the potential benefits of probiotic supplementation in shrimp diets. The enhanced growth performance, better feed efficiency, and improved resistance to both osmotic stress and Vibrio parahaemolyticus infection highlight the role of probiotics in promoting shrimp health and robustness. These benefits are attributed to the probiotics' ability to secrete digestive enzymes and essential nutrients, and to modulate the microbial balance in the shrimp gut.
Dietary supplementation with Bacillus pumilus and Bacillus subtilis significantly improves the growth performance, osmotic stress tolerance, and resistance to Vibrio parahaemolyticus in Whiteleg shrimp. Incorporating probiotics into shrimp feed, alongside optimal farm management and biosecurity protocols, offers a sustainable strategy to enhance shrimp health and mitigate pathogen-related losses.
Figure 1: Mortality recorded over the Vibrio parahaemolyticus challenge performed at the end of the feeding trial (N=240)