Aquaculture continues to expand globally, bringing increasing attention to how its environmental footprint can be managed. Recirculating aquaculture systems (RAS) are often presented as a step forward, yet they still generate CO₂-rich off-gases and nutrient-containing effluents that require handling. These streams are commonly treated as by-products. The study highlighted here, part of the Topical Collection Algal Biotechnology in Wasterwater Treatment, takes a different approach, asking how they might instead be used as inputs for another form of biological production.

The work focuses on Haematococcus pluvialis, a microalga widely studied for its ability to accumulate astaxanthin, a carotenoid with established applications in aquaculture feed, nutraceuticals and beyond. Rather than relying on conventional cultivation media, the authors examine the feasibility of using RAS-derived CO₂ and nutrient flows. This creates a direct connection between two systems that are usually treated separately, linking fish production with microalgal biotechnology.

One aspect of the study is how these alternative inputs influence algal growth and pigment formation. Cultivation conditions are known to shape both biomass productivity and metabolic pathways in microalgae, and H. pluvialis is particularly sensitive to environmental cues when shifting toward astaxanthin accumulation. By working with real effluent streams rather than synthetic media, the study provides insight into how such variability can be managed in applied settings.

Circular bioeconomy

The broader context is the development of circular bioeconomy concepts within aquatic production. Microalgae have long been considered useful for nutrient capture and carbon fixation, with the additional advantage of producing compounds of commercial interest. Integrating them into aquaculture systems offers a way to recover value while addressing environmental concerns, although practical implementation requires careful alignment of biological and engineering parameters.

There are also constraints to consider. Effluent composition can fluctuate, and maintaining consistent productivity under such conditions remains a challenge. Scaling integrated systems introduces further complexity, particularly when balancing the needs of fish culture and algal growth. The study therefore contributes not only by demonstrating feasibility, but also by pointing to areas where further work is needed.

Taken together, the findings add to a growing conversation about how different forms of biomass production can be coupled more closely. Rather than treating waste and production as separate problems, approaches like this suggest a more interconnected perspective. For researchers working in algal biotechnology, aquaculture, or environmental engineering, this intersection continues to open new questions about efficiency, design, and long-term viability.

if you want to see more articles on this topic, visit the Collection: Algal Biotechnology in Wasterwater Treatment of the Journal of Applied Phycology. Submissions are open.

Text and image were created with the assistance of AI.