The growth of the finfish aquaculture industry depends heavily on a traditionally essential but finite resource: fishmeal and fish oil. Faced with pressure on marine resources and price volatility, the industry is urgently seeking sustainable, cost-effective, and nutritious protein alternatives.
A review study recently published in Frontiers in Aquaculture by researchers from the Scottish Association for Marine Science, the University of Dar es Salaam, the University of Kerala, Shantou University, and the University of Stirling, offers a deep and detailed look at the potential of marine macroalgae as a key ingredient in finfish feeds, not only as a source of nutrients, but as a functional additive capable of improving the health and quality of the final product.
The need for new protein sources
Historically, fishmeal has been the protein ingredient of choice in aquaculture due to its high protein content and a nearly perfect amino acid profile for most cultivated species. However, feeds account for over 50% of operating costs in intensive systems, with protein being the most expensive component.
Vegetable alternatives, such as soy, have gained ground but have limitations, such as deficiencies in certain essential amino acids (EAA) and the presence of anti-nutritional factors. It is in this scenario that macroalgae, or seaweeds, emerge as a promising solution.
What do macroalgae offer to fish nutrition?
Macroalgae are divided into three major groups: red (Rhodophyta), green (Chlorophyta), and brown (Phaeophyceae), each with a distinct nutritional profile.
- Proteins and amino acids: Some red algae, such as Porphyra (nori) and Palmaria (dulse), can reach protein contents of up to 47% of their dry weight, comparable to legumes like soybeans. Green algae like Ulva (sea lettuce) also have significant protein levels. Although their total protein content may be moderate, the quality, defined by the proportion of essential amino acids (EAA), is often similar or superior to that of fishmeal and soy.
- Lipids and essential fatty acids: While lipid levels in algae are generally low, they are a valuable source of polyunsaturated fatty acids (PUFA), including long-chain omega-3s like EPA and DHA, which are crucial for the health of many carnivorous marine species.
- Vitamins and minerals: Algae are exceptionally rich in minerals such as iodine, calcium, and iron, surpassing many terrestrial plants. For example, algae of the genus Laminaria are one of the largest accumulators of iodine in nature, which opens the door to the natural fortification of fish fillets.
- Bioactive compounds and functional properties: Perhaps one of the greatest potentials of algae lies not in their macronutrient contribution, but in their wealth of bioactive compounds. Polyphenols, pigments, and especially sulfated polysaccharides (such as carrageenans and fucoidans) have been shown to have immunostimulant, antioxidant, antibacterial, and antiviral properties.
What does science say?
The review analyzes a large number of feeding trials in various fish species, revealing that the response to macroalgae inclusion is dose-dependent and specific to both the algae and fish species.
- Partial replacement inclusion: Most studies suggest that macroalgae can partially replace fishmeal at levels of up to 15% without adverse effects on growth or feed efficiency in many species.
- Carnivores vs. herbivores: As expected, herbivorous and omnivorous species, such as tilapia and carp, tolerate higher inclusion levels than carnivorous species like salmon or sea bass, due to their digestive adaptations. For example, for Mugil cephalus, a 20% inclusion level of Ulva lactuca showed the best growth performance.
- Health benefits: Beyond growth, the inclusion of algae at low levels has been shown to improve the immune response and disease resistance. Trials with European sea bass (Dicentrarchus labrax) and gilthead sea bream (Sparus aurata) showed that diets supplemented with Gracilaria and Ulva improved antioxidant response and resistance to pathogens.
- Final product quality: Algae supplementation can improve fillet quality. In Atlantic salmon, the inclusion of Palmaria palmata not only improved liver health but also imparted a yellow/orange color to the fillet, presenting itself as an alternative to synthetic pigments.
Challenges and the path forward
Despite the enormous potential, there are limitations. The main obstacle for macroalgae to replace a larger proportion of fishmeal is their lower total protein concentration and the high presence of indigestible components such as fiber and ash. The complex polysaccharides in the cell walls of algae can limit the digestibility of proteins.
The solution could lie in processing. As with soy, the development of algae protein concentrates, where non-protein components are removed, could be key to creating a high-quality ingredient comparable to traditional ones. Furthermore, the use of enzymes to break down cell walls has been shown to improve the digestibility of nutrients.
Conclusion
The study concludes that while macroalgae may not be a total replacement for fishmeal in their raw form, their true value lies in their strategic use. Whether as a partial substitute of up to 15% or as a functional “micro-ingredient” at low levels (1-5%), seaweeds offer a way to improve sustainability, profitability, and health in aquaculture.
The ability of macroalgae to enhance the immune response, stress resistance, and nutritional quality of fish for the final consumer positions them as a fundamental component in the formulation of future feeds: more natural, healthier diets in harmony with the demands of the planet and the market.
Reference (open access)
Hughes, A. D., Twigg, G. C., Msuya, F. E., Padmakumar, K. P., & Tocher, D. R. (2025). The use of macroalgae in feeds for finfish aquaculture. Frontiers in Aquaculture, 4, 1570842. https://doi.org/10.3389/faquc.2025.1570842
Editor at the digital magazine AquaHoy. He holds a degree in Aquaculture Biology from the National University of Santa (UNS) and a Master’s degree in Science and Innovation Management from the Polytechnic University of Valencia, with postgraduate diplomas in Business Innovation and Innovation Management. He possesses extensive experience in the aquaculture and fisheries sector, having led the Fisheries Innovation Unit of the National Program for Innovation in Fisheries and Aquaculture (PNIPA). He has served as a senior consultant in technology watch, an innovation project formulator and advisor, and a lecturer at UNS. He is a member of the Peruvian College of Biologists and was recognized by the World Aquaculture Society (WAS) in 2016 for his contribution to aquaculture.
