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Shrimp grow better at low densities in Biofloc systems

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By Milthon Lujan

Biofloc
Biofloc

Looking for a more sustainable way to cultivate shrimp? Biofloc systems (BF) are gaining ground for their ecological approach. But how many shrimp can realistically be raised in a BF tank?

A new study published by researchers from Suez University (Egypt) sheds light on the ideal population density for optimal health and growth of Pacific white shrimp (Litopenaeus vannamei) in a biofloc system. They compared shrimp growth performance in low-density (LD) culture ponds with 50 organisms/m2 and high density (HD) ponds with 200 organisms/m2.

Advantages of Biofloc

Traditional shrimp farming often relies on intensive water exchange and can contribute to environmental pollution. In this context, biofloc systems offer a closed-loop solution. They cultivate a beneficial community of microorganisms (the “floc”) that naturally cleans the water and even serves as a supplementary food source for shrimp.

The use of biofloc systems reduces reliance on external feed and minimizes water wastage, making BF systems a promising pathway for sustainable shrimp aquaculture.

Challenges of Overcrowding

While BFT offers numerous benefits, high population densities can be detrimental. Overcrowding can lead to:

  • Stress from competition for food, space, and territory.
  • Poor growth: Limited resources can hinder shrimp development.
  • Water quality issues: Excessive waste from a concentrated population can overload the system.
  • Increased risk of diseases: Overcrowded conditions can favor the growth of harmful bacteria.

Population Density Matters

This study investigated the impact of population density on the performance of Pacific white shrimp (Litopenaeus vannamei) in BF systems. Shrimp were raised in low-density (LD) ponds with 50 shrimp per square meter or high-density (HD) ponds with 200 shrimp per square meter. After 16 weeks, the results were clear:

  • Survival and Growth: Shrimp in the LD group had significantly higher survival rates, grew faster, and consumed more feed compared to their HD counterparts.
  • Biofloc Quality: The biofloc in the LD system had higher protein content (16.63% vs. 15.21%), likely contributing to the superior growth performance of the shrimp.
  • Microbial Balance: While overall bacterial counts in the water remained similar between groups, the HD system harbored a higher abundance of potentially harmful Vibrio bacteria.
  • Shrimp Health: Analysis revealed that shrimp in the LD group had higher protein and lipid content, indicating better overall health. In contrast, the HD group showed signs of stress, with elevated levels of total aerobic bacteria and the presence of undesirable bacteria such as Salmonella enterica. Additionally, Vibrio levels were significantly higher in HD shrimp.
  • Stronger Immune System: Gene expression analysis revealed significantly elevated levels of genes related to the immune system in LD shrimp, suggesting a more robust defense system. In contrast, HD shrimp showed higher gene expression related to stress.
  • Efficient Digestion: LD shrimp showed higher activity of digestive enzymes such as amylase, lipase, and protease, indicating better nutrient utilization.
  • Reduced Oxidative Stress: Antioxidant enzyme activity was significantly higher in LD shrimp, which could aid in stress resistance.
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High Density Brings Challenges

While high density may seem appealing for increasing production, this study highlights potential drawbacks:

  • Microbial Imbalance: Vibrio levels were significantly higher in the HD group, posing a potential threat to shrimp health.
  • Pathogen Presence: The HD group showed the presence of Salmonella enterica ssp. arizonae, a concerning bacterium in aquaculture.
  • Gill Damage: Histological examination revealed negative effects on the gills of HD shrimp, suggesting potential respiratory issues.

Conclusion

This research emphasizes the importance of population density in BF systems. Lower densities promote healthier shrimp with better growth, immunity, and digestive efficiency. By optimizing population density, along with other factors such as carbohydrate source and feeding management, BF systems can truly revolutionize sustainable shrimp farming.

Open access to the publication has been funded by The Science, Technology & Innovation Funding Authority (STDF) in cooperation with The Egyptian Knowledge Bank (EKB).

Contact
Haitham G. Abo-Al-Ela
Genetics and Biotechnology, Department of Aquaculture, Faculty of Fish Resources, Suez University
Suez, 43221, Egypt
Email: haitham.aboalela@frc.suezuni.edu.eg

Reference (open access)
Said, M. M., G., H., A., Y., Ahmed, O. M., & Dighiesh, H. S. (2024). Influence of stocking density on the growth, immune and physiological responses, and cultivation environment of white-leg shrimp (Litopenaeus vannamei) in biofloc systems. Scientific Reports, 14(1), 1-15. https://doi.org/10.1038/s41598-024-61328-4