On June 17, 2025, Sun et al. from the Department of Aquaculture at Zhejiang Ocean University published an article in the journal Metabolites entitled "Impact of Dietary Carbohydrate Levels on Growth Performance, Feed Efficiency, and Immune Response in Litopenaeus vannamei Cultured in Biofloc Systems." The research provides a critical analysis of how biofloc technology (BFT) modifies the nutritional requirements of high-value aquatic species. The study reveals that L. vannamei exhibits a significantly higher tolerance and utilization efficiency for dietary carbohydrates when raised in BFT environments compared to traditional systems, with optimal levels identified between 31.44% and 31.77%. By mapping the enzymatic shifts in glycolysis and gluconeogenesis, the authors demonstrate that BFT acts as a metabolic buffer, enhancing growth performance while mitigating oxidative stress, thus paving the way for more sustainable, low-nitrogen Carbohydrate Manufacturing for the aquaculture industry.

Metabolic Synergies in Sustainable Biofloc Environments

The intensification of global aquaculture has reached a critical juncture where the dual pressures of environmental sustainability and operational profitability necessitate a fundamental shift in feed formulation and water management. Traditionally, intensive shrimp farming has been plagued by the accumulation of ammonia and nitrite, toxic byproducts of protein metabolism and uneaten feed. Biofloc technology (BFT) has emerged as a transformative solution, leveraging a high carbon-to-nitrogen (C/N) ratio to stimulate the growth of heterotrophic microbial communities. These microbes effectively recycle inorganic nitrogen into protein-rich bioflocs, which serve as a continuous, supplemental nutrient source for the cultured organisms.

Carbohydrates are not only the primary energy source for the shrimp but also the "fuel" for the biofloc community. While traditional mariculture often limits carbohydrate inclusion due to the poor glycemic control observed in many crustaceans, the integration of BFT suggests a higher threshold for sugar utilization. Understanding the precise interplay between dietary carbohydrate levels and the BFT-mediated microbial environment is essential for developing "protein-sparing" diets. By replacing expensive and environmentally taxing fish meal proteins with optimized Carbohydrate Sources like Corn Starch, manufacturers reduce feed costs and minimize nitrogenous waste, aligning with the principles of the circular bioeconomy.

Analyzing Growth Metrics and Feed Conversion Efficiency

The researchers conducted a meticulous eight-week trial utilizing five isonitrogenous and isolipidic diets with carbohydrate levels ranging from 11% to 47%. The experimental design aimed to pinpoint the exact concentration at which carbohydrates maximize growth without inducing metabolic dysfunction. The results demonstrated a clear parabolic relationship between carbohydrate intake and growth performance. As inclusion levels increased from 11% to 38%, there was a significant enhancement in final body weight (FBW), weight gain (WG), and specific growth rate (SGR).

Fig.1 Water quality in the BFT system under varying dietary carbohydrate levels. (Sun, et al., 2025)

Notably, the 38% carbohydrate group (C38) exhibited the most robust growth profile, contrasting sharply with the 11% group, which showed a significantly higher feed conversion ratio (FCR) and lower protein efficiency ratio (PER). This indicates that at low carbohydrate levels, shrimp are forced to utilize dietary protein for energy rather than tissue synthesis, a phenomenon known as "protein wasting." Through piecewise regression analysis, the study determined that the optimal dietary carbohydrate range for L. vannamei in a BFT system is 31.44-31.77%. This finding is an innovation in itself, as it surpasses the typical 20-25% recommendation for traditional aquaculture, proving that the BFT environment fundamentally alters the shrimp's nutritional "sweet spot."

Fig.2 PER and FCR as functions of dietary carbohydrate levels. (Sun, et al., 2025)

Enzymatic Orchestration of Hepatopancreatic Carbohydrate Metabolism

A pivotal aspect of this research is the deep dive into the hepatopancreas, the central metabolic organ of the shrimp, to observe how dietary sugar levels influence enzyme activity. The study measured key regulators of the glycolytic pathway, such as pyruvate kinase (PK) and phosphofructokinase (PFK), alongside critical gluconeogenic enzymes, namely phosphoenolpyruvate carboxykinase (PEPCK) and glucose-6-phosphatase (G6Pase). The findings revealed a sophisticated metabolic adaptation: as dietary carbohydrates increased, the shrimp upregulated the expression of PK and PFK, effectively accelerating the breakdown of glucose to generate ATP.

Fig.3 Amylase and carbohydrate metabolic enzyme activities in L. vannamei within the BFT system, as influenced by dietary carbohydrate levels. (Sun, et al., 2025)

Simultaneously, the researchers observed a marked downregulation of PEPCK and G6Pase. This suppression of gluconeogenesis is a logical physiological response to an abundance of exogenous glucose; the organism conserves energy by halting the internal synthesis of sugar. This enzymatic "push-pull" mechanism explains why L. vannamei thrives on higher-carbohydrate diets in BFT systems. The microbial nutrition provided by the biofloc likely provides essential cofactors and secondary metabolites that support this heightened glycolytic flux. However, the study also identified a metabolic ceiling. At the extreme 47% carbohydrate level, the system began to show signs of strain, suggesting that even with microbial assistance, the crustacean hepatopancreas has a finite capacity for processing concentrated carbohydrate loads.

Immune Resilience and the Mitigation of Oxidative Stress

Beyond growth and metabolism, the study investigated the impact of carbohydrate levels on the shrimp's innate immune system and oxidative status. In aquaculture, high-sugar diets are often associated with hyperglycemia-induced stress and immunosuppression. The researchers monitored markers such as superoxide dismutase (SOD), catalase (CAT), and malondialdehyde (MDA), as well as lysosomal enzymes like acid phosphatase (ACP) and alkaline phosphatase (AKP).

Fig.4 Antioxidant enzyme activity in L. vannamei within the BFT system as influenced by dietary carbohydrate levels. (Sun, et al., 2025)

The results showed that BFT provides a significant protective effect. While the activities of SOD and CAT remained relatively stable across most groups, indicating a well-managed antioxidant defense, the 47% carbohydrate group eventually succumbed to oxidative stress, evidenced by a significant spike in MDA levels. Furthermore, the highest carbohydrate group showed a decline in hemolymph total protein and ACP activity, suggesting a compromised immune state. Interestingly, the study found that BFT systems partially mitigate these negative effects compared to traditional systems by enhancing lysosomal enzyme activity. This suggests that the biofloc itself may act as an "immunostimulant," providing the shrimp with a higher baseline of resilience against dietary imbalances. The innovation here lies in the confirmation that while BFT expands the metabolic window for carbohydrates, careful monitoring is still required to avoid the tipping point of oxidative damage.

Advantages and Innovations

• Redefinition of Nutritional Thresholds: The study identifies a significantly higher optimal carbohydrate level (31.44-31.77%) for L. vannamei in BFT systems than previously reported for traditional systems. This provides a scientific basis for the manufacturing of high-energy, low-protein feeds that utilize sustainable carbohydrate sources more aggressively.
• Mechanistic Mapping of Metabolic Plasticity: By quantifying the reciprocal regulation of glycolysis (PK, PFK) and gluconeogenesis (PEPCK, G6Pase) in response to dietary load, the research offers a blueprint for understanding metabolic flux in crustaceans. This allows for the precise engineering of diets that align with the organism's natural enzymatic capacity.
• Holistic Integration of Microbiome and Metabolism: The research demonstrates that the BFT microbial environment serves as a "metabolic auxiliary," enhancing carbohydrate utilization and mitigating oxidative stress. This highlights the potential for "synbiotic" aquaculture where feed formulation and microbial management are developed as a single, integrated technology.

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Conclusion

By proving that BFT facilitates a more efficient utilization of carbohydrates in L. vannamei, the authors have provided the industry with a clear path toward reducing nitrogen emissions and lowering production costs through protein sparing. The discovery of a specific metabolic adaptation, the upregulation of glycolytic enzymes coupled with the suppression of gluconeogenesis, offers a mechanistic explanation for the success of carbohydrate-rich diets in these systems. For the carbohydrate manufacturing sector, these findings encourage the development of specialized, functional carbohydrate blends designed specifically for BFT-based aquaculture. As we move toward a future of zero-water exchange and high-density farming, the ability to fine-tune the carbohydrate-to-protein ratio will be the key to balancing rapid growth with robust animal health and environmental stewardship.