WWW.WAS.ORG • WORLD AQUACULTURE • DECEMBER 2025 43 (CONTINUED ON PAGE 44) Figure 1. Benefits of Thraustochytrid-rich feeds in Sustainable Aquaculture nutritional requirements of farmed aquatic animals and the overarching sustainability goals of the aquaculture sector. The Nutritional Imperative: Omega-3s in Aquaculture Long-chain polyunsaturated fatty acids (LC-PUFAs), specifically docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA), are indispensable components of aquatic animal diets. Unlike terrestrial livestock, most farmed fish and shellfish have a limited capacity to synthesize these crucial fatty acids de novo, making dietary inclusion essential (Parrish 2024). Within aquaculture species, DHA and EPA play pivotal roles in a myriad of physiological processes, including optimal growth and development, reproductive success, visual acuity, neural function, and robust immune responses. Deficiencies in these lipids can lead to reduced growth rates, increased susceptibility to disease, poor feed conversion efficiency, and diminished stress tolerance, ultimately impacting the productivity and profitability of aquaculture operations. Beyond the health and performance of the cultured organisms, the nutritional composition of farmed seafood has a direct impact on human health. Seafood, particularly fatty fish, is widely recognized as a primary dietary source of DHA and EPA for humans, offering significant benefits for cardiovascular health, cognitive function, and the regulation of inflammation. As aquaculture supplies an everincreasing proportion of global seafood consumption, ensuring that farmed fish are rich in these beneficial omega-3s is vital for public health. Traditionally, fish oil, derived from wild-caught forage fish, has been the primary source of LC-PUFAs in aquafeeds. While highly effective, this reliance presents a significant bottleneck for sustainable aquaculture growth. The global supply of fish oil is finite and largely static, while the demand from the burgeoning aquaculture industry continues to climb. This imbalance leads to volatile prices, ethical concerns regarding ecosystem impacts, and questions about the long-term sustainability of the entire feed value chain (Jaseera and Kaladharan 2019). The imperative to find viable, scalable, and sustainable alternatives to bridge this growing ‘omega-3 gap’ is therefore more critical than ever for the future of aquaculture. Thraustochytrids: A Closer Look Amidst the search for sustainable omega-3 alternatives, marine heterotrophic protists belonging to the order Thraustochytriales, commonly known as thraustochytrids, have emerged as star candidates. These fascinating single-celled organisms are broadly classified within the Stramenopiles and are ubiquitous in marine environments, inhabiting diverse niches from coastal waters to deep-sea sediments (Raghukumar 2008). Unlike microalgae, which rely on photosynthesis, thraustochytrids are heterotrophic, meaning they derive their energy from organic matter (Leyland et al. 2017). This characteristic makes them exceptionally wellsuited for industrial cultivation. Their standout feature lies in their remarkable metabolic capacity to accumulate high levels of lipids, particularly LC-PUFAs, within their cells. Specific genera and species, such as Schizochytrium sp. and Aurantiochytrium sp., are renowned for their ability to synthesize significant quantities of DHA, and in some strains, EPA, through a process of controlled fermentation (Raghukumar 2008, Yokochi et al. 1998). This makes them a direct and potent source of the very fatty acids that are critical for aquaculture. The cultivation of thraustochytrids offers several distinct advantages over traditional fish oil production or even photosynthetic microalgae. They can be grown rapidly in large-scale bioreactors under controlled and sterile conditions, mitigating issues associated with seasonal variability, land use, and weather dependency that affect conventional agricultural crops. Their heterotrophic nature means they do not require light, simplifying bioreactor design and operation. Furthermore, thraustochytrid biomass can be produced using various cost-effective carbon sources, including agricultural by-products and industrial waste streams (Wang et al. 2024), aligning perfectly with circular bioeconomy principles and reducing the environmental footprint of production (Yamasaki et al. 2006). This controlled, high-yield fermentation process ensures a consistent and reliable supply of high-quality omega-3-rich biomass, free from the heavy metals and contaminants often found in wild fish. Beyond Omega-3s: Functional Bioactives While the high concentration of DHA and EPA is a primary driver for the inclusion of thraustochytrids in aquafeeds, their nutritional profile extends far beyond these essential fatty acids. Thraustochytrids are also a rich source of various functional bioactives that offer additional benefits for the health, welfare, and quality of farmed aquatic species. These compounds contribute to improved pigmentation, antioxidant defense, and immune modulation, making thraustochytrid biomass a holistic feed ingredient (Figure 1). Prominent among these bioactives are carotenoids, particularly astaxanthin. This potent antioxidant is Thraustochytrids are marine, non-photosynthetic microorganisms that naturally produce high levels of omega-3s like DHA, along with valuable antioxidants. Grown through fermentation, they offer a sustainable alternative to fish oil in aquafeeds.
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