In a groundbreaking advancement blending innovative aquaculture technology with gastronomy, Okayama University of Science (OUS) has unveiled its latest premium aquaculture product: the “Okayama Ridai Matsukawa-garei,” a cultivated flounder raised in a revolutionary water system known as the “Third Water.” This pioneering method has enabled the university to cultivate a species traditionally challenging to farm, delivering a delicate and richly flavored fish that has now made its commercial debut on the sushi conveyor belt at the prestigious Kurasushi Osaka Expo 2025 branch.
The “Third Water” aquaculture system represents a significant scientific breakthrough—an environment where both freshwater and seawater species coexist effectively within a controlled, closed recirculating tank. This technological innovation by OUS’s Education and Research Center for Biological Production allows for the cultivation of the Matsukawa flounder (Matsukawa-garei), a species noted for its thick, succulent flesh, complex fat profile, and naturally sweet flavor. By precisely modulating water salinity, temperature, oxygen levels, and nutrient balance, this system mimics the transitional aquatic environments flounders encounter in nature, vastly improving survival rates and growth quality.
Introduced to the public on July 25, 2023, the Matsukawa flounder was stocked initially as juveniles averaging 2.6 grams and 6 centimeters in length. The fish were nurtured meticulously in a 35-ton, fully closed recirculating tank system designed to maintain optimal growth conditions. The recirculating aquaculture system (RAS) employed here cycles water continuously through mechanical and biological filtration processes, ensuring the removal of waste products and the maintenance of pristine water quality. This allows for minimal environmental impact and resource efficiency, key components as aquaculture strives to meet rising global seafood demand sustainably.
The cultivation process spans several months, during which the Matsukawa flounder exhibit steady growth until reaching an average market weight of approximately 1.5 kilograms. The relatively rapid growth rate underscores the efficacy of the Third Water method in providing a stable and nutrient-rich environment. Moreover, the system’s closed nature provides robust biosecurity, reducing disease transmission risks and antimicrobial use compared to traditional open-sea aquaculture farms.
Recognized in culinary circles as the “King of Flounder,” Matsukawa carries prized gastronomic qualities. Its thick flesh boasts a distinct firmness paired with a luxurious layering of natural fats and subtle sweetness—a profile highly sought after in premium sushi preparation. At Kurasushi’s Osaka Expo 2025 branch, this delicacy is served as nigiri, featuring the flounder atop vinegared rice and enhanced with a soy-sauce koji marinade, a traditional fermentative dressing that complements the fish’s umami characteristics.
This commercial launch marks the second successful collaboration between OUS and Kurasushi leveraging the Third Water system. Earlier in May 2023, the market saw the introduction of “Okayama Ridai Unagi,” a similarly cultivated eel product that achieved nationwide distribution. The expansion of this innovative aquaculture branding at Kurasushi reaffirms the potential for integrated scientific research to reshape aquaculture and culinary sectors alike.
Kurasushi’s Osaka Expo 2025 branch, boasting 338 seats and an impressive 135-meter conveyor belt lane, offers patrons a diverse global menu in line with the Expo’s international cultural ethos. The integration of OUS’s Matsukawa flounder into such a high-capacity, cutting-edge venue highlights the technological and culinary prestige accreted around this new product. Early customer reactions have been overwhelmingly positive; a young Osaka local praised the fish’s perfectly balanced texture and flavor profile, bringing out its firm yet slightly crunchy flesh and elegant sweetness.
Associate Professor Toshimasa Yamamoto from OUS’s Faculty of Life Sciences, who supervises the aquaculture research, remarked on the emotional and scientific dedication behind this accomplishment. He highlighted the student researchers’ meticulous care throughout the cultivation process, likening their nurturing to raising children. Beyond mere commercial success, Yamamoto envisions the Matsukawa flounder as a symbol of Japan’s cutting-edge biological production research, aiming to attract global attention to the university’s innovative aquaculture capabilities.
The underlying science of the Third Water system entails complex hydrological and biochemical engineering challenges. Creating an aquatic milieu suitable for both freshwater and marine organisms requires precise control of ionic concentrations, osmotic pressures, and microbial communities. Advanced sensors continuously monitor physicochemical parameters, feeding data into real-time automated regulation systems to maintain steady-state conditions. This dynamic equilibrium fosters optimal metabolic rates within the flounder, enhancing growth efficiency and flesh quality.
From an environmental perspective, the recirculating aquaculture approach aligns with the broader goals of sustainable seafood production—reducing reliance on wild fish stocks, minimizing nutrient runoff, and curbing antibiotic dependence. The closed-loop system exemplifies how university-led research can translate into commercially viable, eco-conscious food sources fitting modern consumer preferences and regulatory standards.
The commercial acceptance of Matsukawa flounder also owes much to evolving consumer trends favoring traceability, welfare-conscious farming, and novel gourmet experiences. Labeling the product as “Okayama Ridai Matsukawa-garei” emphasizes regional pride and scientific pedigree, enriching the narrative behind consumers’ dining experience. This fusion of cutting-edge science with cultural appreciation may catalyze wider adoption of innovative aquaculture products in global markets.
Looking forward, OUS aims to further refine the Third Water system for additional species and explore genomic, immunological, and nutritional optimization to enhance farmed fish resilience and flavor attributes. Such multidisciplinary research integrating biology, engineering, and food science heralds a future where aquaculture can sustainably meet increasing demands without compromising quality or environmental integrity.
In summary, the commercial debut of Matsukawa flounder at Kurasushi’s flagship Osaka Expo 2025 branch represents a landmark integration of innovative aquaculture technology with culinary excellence. The union of OUS’s Third Water system and a major sushi chain not only offers consumers an extraordinary dining experience but also showcases Japan’s leadership in scientific aquaculture research. This progress underscores the transformative potential of university-industry collaboration in crafting sustainable, premium food solutions designed for the future.
Subject of Research: Innovative aquaculture of Matsukawa flounder using the Third Water recirculating system at Okayama University of Science.
Article Title: Okayama University of Science Launches Premium “Okayama Ridai Matsukawa-garei” Cultivated Flounder at Kurasushi Osaka Expo 2025 Branch
News Publication Date: July 25, 2023
Web References:
https://mediasvc.eurekalert.org/Api/v1/Multimedia/ff7bcb8d-966f-44d1-a875-eb735c92f161/Rendition/low-res/Content/Public
Image Credits: Okayama University of Science
Keywords: Matsukawa flounder, Third Water aquaculture, recirculating aquaculture system, sustainable seafood, Okayama University of Science, Kurasushi, Osaka Expo 2025, premium sushi, aquaculture innovation, biological production, closed-loop system, gourmet aquaculture
