A new study led by Assistant Professor Pallab Sarkar at the University of California, Santa Cruz, demonstrates that microalgae can serve as an affordable and nutritionally viable replacement for fishmeal in the diets of farmed rainbow trout. This breakthrough in aquaculture feed formulations could reduce the reliance on wild fish stocks and alleviate pressure on ocean ecosystems. The study builds on previous research that sought to replace traditional fishmeal with Nannochloropsis, a species of microalgae.
In their two-month growth study, researchers fed over 500 rainbow trout diets containing varying levels of microalgae, replacing fishmeal in amounts ranging from 33% to 100%. The results showed no significant difference in the growth of the fish compared to those fed a conventional diet. Furthermore, the nutritional value for humans and the cost-effectiveness of the microalgal-based feed were comparable to traditional fishmeal-based diets. This success suggests that microalgae could become a sustainable and economical alternative to fishmeal, helping reduce the environmental impact of aquaculture.
The researchers are now focused on further improving the feed formulations by replacing fish oil, aiming to create a fully fish-free feed. They are also exploring the possibility of increasing the amount of microalgae used to replace other land-based agricultural ingredients, potentially improving the nutritional profile of the fish and lowering the carbon footprint of the feed. Their long-term goal is to contribute to the development of diverse, high-quality, fish-free feed options for the aquaculture industry.
Professor Sarkar emphasized the importance of aquaculture in global food production, noting that half of the fish consumed worldwide are farmed. However, the growing demand for fish has often led to overfishing and environmental degradation. By shifting away from wild fish-derived feed ingredients, the industry could expand sustainably without further stressing ocean ecosystems.
The team’s research was not without challenges, particularly when it came to feeding rainbow trout. Unlike tilapia, which are naturally herbivorous, trout are carnivores with a preference for the taste and smell of fishmeal. Earlier attempts to replace fishmeal with microalgae resulted in poor growth, but the researchers identified that trout’s aversion to the microalgae’s taste was a major obstacle. They overcame this by adding taurine and lecithin, natural compounds found in fishmeal, to improve the feed’s palatability. Additionally, new processing techniques, such as using high-temperature extrusion to form pellets, contributed to the success of the microalgae-based diet.
Although the results are promising, Sarkar cautioned that microalgae production must become more cost-effective for widespread use in aquaculture feeds. Currently, the only affordable method for incorporating Nannochloropsis into fish feed is by recycling leftovers from human dietary supplements. Scaling up microalgae production specifically for aquaculture will be essential to making these feed alternatives a sustainable industry standard.
Overall, this research marks a significant step towards creating more sustainable and cost-effective solutions for the aquaculture industry, with the potential to reduce reliance on wild fish stocks and minimize environmental impacts.
Source: HatchBlue
