Combating Vibrio harveyi infections in shrimps with microalgae supplements

Disease outbreaks (particularly Vibrio species) in aquaculture can affect production and trade in various parts of the world. There has been much development into antibiotic resistance, however the popular use of antimicrobials for disease control has been seen to have hazardous effects to human health, as it encourages bacterial resistance. Studies have shown that the use of microalgae as live feed in aquaculture can reduced the levels of bacterial diseases. This study by Seraspe et al., (2014) looks at using Chaetoceros calcitrans, a unicellular and eukaryotic diatom, as a supplement in the diet of Penaeus monodon to control Vibrio harveyi infection. Total lipid and fatty acid profile of Chaetoceros calcitrans was also analyzed to determine the presence of polyunsaturated fatty acids (PUFAs) which are considered important in the treatment and prevention of diseases. 

Cultures of Chaetoceros calcitrans were obtained, freeze-dried and mixed to form the basal diet at 15 and 30g/kg diet. Feed incorporated with Curdlan was used as a positive control. Penaeus monodon postlarvae were obtained and fed all the same feeds up until an average weight of 10g, and then were fed either Chaetoceros calcitrans (15g/kg diet or 30g/kg diet) or a control of Curdlan. They were then subjected to a bacterial challenge test with virulent Vibrio harveyi (via intramuscular injection). Relative percentage survival (RPS) was computed based on a formula. Immune responses were noted after exposure including prophenoloxidase activity (proPO) which involved the production of protein and as an index to measure general activation of the immune response, along with plasma protein concentration. 

Results showed that the microalgal diet did not affect general growth and survival of the shrimp. However, after exposure to the Vibrio harveyi challenge, the microalgal supplementation did affect the shrimp’s survival. Decreased mortality rates were seen in shrimps fed the supplement of Chaetoceros calcitrans, along increased span of time till 80% mortality was reached (if occurred). There was also higher prophenoloxidase activity in shrimps fed Chaetoceros calcitrans, indicated an enhanced immune response against bacterial diseases. This could be due to the high fatty acid content found in Chaetoceros calcitrans, which are known to have antibacterial effects.

Overall, the use of microalgae as a supplement in preventing and treating bacterial diseases could provide opportunities against infectious diseases, particularly with Vibrio species in aquaculture. This could possibly be incorporated into marine habitats themselves, especially with how the increase in sea-surface temperature comes with an increase in Vibrio species.

Reference:

Seraspe, E., Gabotero, S., De la Peña, M., Pahila, I. and Amar, E. (2014). Evaluation of dietary freeze-dried Chaetoceros calcitrans supplementation to control Vibrio harveyi infection on Penaeus monodon juvenile. Aquaculture, 432, pp.212-216.