Fine-Tuning Macro- and Micronutrients in Sturgeon Diets 

Global demand for sturgeon meat is driving more intensive production, where farming practices, i.e. transport and high stocking densities, expose fish to crowding events that induce stress and impair immune function. As part of overcoming these stressful factors, feed formulations needs to  fine-tune macronutrients while balancing specific micro-nutrients that support performance and robustness of fish. This study, led by Keke Zheng and Anne Kristine Hansen, explores how targeted adjustments in dietary protein, lipid, and omega-3 fatty acids affect growth, welfare, and harvest quality in hybrid sturgeon. 

Two trials were carried out with hybrid sturgeon (A. baerii ♀ x A. schrencki ♂) at Zhejiang Ocean University, China. Firstly, an 8-week growth trial with juvenile fish (initial weight 135 g, final weight approximately 420 g), using nine extruded diets developed through a Central Composite Design to vary dietary protein and lipid levels. Secondly,  sturgeon (initial weight 110 g, final weight approximately 700 g) were fed for 15 weeks under optimal conditions with graded dietary levels of EPA + DHA, from 3.3% to 30.9% of total fatty acids. An acute crowding challenge was conducted to mimic transportation practices at the end of each trial: 180 kg/m³ in the first trial and 260 kg/m³ in the second. All experimental procedures complied with the national guidelines for the care of laboratory animals in China and were approved and monitored by the Animal Ethics Committee of Zhejiang Ocean University. 

Results 

Growth and Feed Performance 

In the first trial, surface response models integrating dietary protein and lipid were developed to optimize key outcomes, including specific growth rate (SGR), feed conversion ratio (FCR), protein retention, and somatic indices. In the second trial, growth and feed performance were not affected by EPA + DHA levels within the range tested, indicating that the standard requirement is met across the inclusion range. 

Immune and Inflammatory Response 

During the stressful event, high-lipid diets consistently induced higher TGFβ1 expression, suggesting enhanced immunoregulatory signalling and increased investment in tissue remodelling and repair. TNFα expression was jointly affected by dietary protein and lipid, with the most nutrient-dense formulations showing higher expression, consistent with stronger pro-inflammatory and innate immune activation. 

Skin and Flesh Quality After Crowding 

On the other hand, increasing dietary EPA + DHA reduced the severity of bleeding spots and yellow discoloration on the skin belly after the crowding challenge. While EPA + DHA did not affect growth, higher levels improved harvest quality under stress conditions.

The results show that fine-tuned formulations for sturgeon are needed to support not only growth but robustness. For example, high-lipid, nutrient-dense formulations strengthen resilience to crowding stress by modulating key immune functions, while higher EPA + DHA inclusion improved post-stress skin and flesh condition. As sturgeon production becomes more intensive, formulations that account for both performance and physiological resilience will be crucial to protect welfare and harvest quality of the fish and to sustain the existence and expansion of the industry.