Valorisation of invasive North Sea macroalgae as functional feed additives to improve disease resilience in Pacific white shrimp (Litopenaeus vannamei)
This study demonstrates that incorporating extracts from invasive North Sea macroalgae, particularly *Ulva australis* from the Netherlands, into Pacific white shrimp diets significantly enhances survival rates against *Vibrio parahaemolyticus* infection by modulating gut microbiome composition, despite not improving overall growth performance.
Original paper licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer
The ocean is a vast, dynamic system where life thrives in delicate balance, but human activity has introduced new players that disrupt this equilibrium. Along the coastlines of Europe, certain types of seaweed, originally from distant waters, have arrived and multiplied, crowding out native plants and altering the local ecosystem. These are known as invasive species, and while they pose an ecological challenge, they also represent a massive, untapped resource. At the same time, the global demand for food is driving a rapid expansion in aquaculture, the farming of aquatic animals like shrimp. This industry faces a persistent threat: disease. Bacterial infections can wipe out entire harvests, leading farmers to rely heavily on antibiotics, a practice that is increasingly discouraged due to environmental and health concerns. Scientists are therefore searching for natural alternatives that can boost the health and disease resistance of farmed shrimp without harming the environment. The question at the heart of this research is whether these troublesome, invasive seaweeds can be transformed from an ecological nuisance into a powerful tool for protecting farmed shrimp.
Researchers at Ghent University and the Royal Netherlands Institute for Sea Sea Research set out to test this idea using two specific types of invasive seaweed found in the North Sea: a green seaweed called Ulva australis and a brown seaweed known as Sargassum muticum. They collected these plants from the coasts of the Netherlands, France, and Belgium, drying them and grinding them into a fine powder. From this powder, they extracted a liquid rich in plant chemicals, specifically focusing on compounds known as phenolics, which are natural substances found in many plants that can act as antioxidants and antimicrobial agents. The team first tested these extracts in a laboratory setting against Vibrio parahaemolyticus, a dangerous bacterium that causes a severe and often fatal disease in shrimp known as acute hepatopancreatic necrosis disease. The results were promising; the seaweed extracts were able to slow down or stop the growth of the bacteria. The extract from the Dutch Ulva australis was particularly effective, requiring a lower concentration to inhibit the bacteria compared to the others.
Encouraged by these laboratory results, the scientists moved to a living experiment. They raised young Pacific white shrimp, the most common species farmed globally, in tanks and fed them a diet mixed with small amounts of the seaweed extracts. Some shrimp received a diet with one percent of the extract, while others received three percent. A control group was fed a standard commercial diet with no seaweed. The researchers wanted to see if the seaweed would help the shrimp grow faster or survive better. After a month of feeding, they challenged the shrimp by exposing them to the harmful Vibrio bacteria. The outcome was clear and significant. The shrimp that had eaten the seaweed-supplemented food survived the bacterial attack at much higher rates than the shrimp on the standard diet. The group fed the three percent Dutch Ulva australis extract showed the strongest protection, with survival rates rising from sixty percent in the control group to nearly seventy-five percent in the treated group. This improvement was not just a small fluctuation; it was a statistically significant difference that points to a real biological benefit.
However, the story was not a simple tale of seaweed making everything better. While the treated shrimp were better at surviving the disease, they did not grow as fast as the shrimp on the standard diet. In fact, the control group, which ate no seaweed, gained more weight and converted their food into body mass more efficiently. This suggests that the seaweed extracts are not growth promoters in the traditional sense. Instead, they appear to function as a shield, priming the shrimp's immune system or altering their internal biology to better withstand infection. The researchers also looked inside the shrimp to see how the seaweed affected their gut microbiome, the community of bacteria living in their digestive tract. They found that the seaweed diets did change the types of bacteria present, shifting the balance of the microbial community, but the overall variety of bacteria remained similar across all groups. This indicates that the seaweed is subtly reshaping the shrimp's internal environment to favor health, rather than simply adding more beneficial bugs.
The study concludes that these invasive North Sea macroalgae hold genuine potential as functional ingredients for shrimp feed. They are not a magic bullet that solves every problem, nor do they replace the need for good farming practices. Instead, they offer a specific, valuable advantage: the ability to help shrimp survive disease outbreaks that would otherwise be devastating. By turning a problematic invasive species into a feed additive, the industry could simultaneously address an ecological issue and improve animal health, reducing the need for antibiotics. The researchers note that while the current results are encouraging, more work is needed to understand exactly which chemical compounds are doing the heavy lifting and to determine the perfect amount to add to the feed. For now, the findings offer a hopeful glimpse into a future where the ocean's unwanted guests might become essential allies in sustainable food production.
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