The quest for more sustainable aquaculture is driving the search for alternatives to fishmeal (FM) and fish oil (FO), which are finite resources with fluctuating costs. In this context, ingredients derived from low-trophic-level organisms, such as microalgae, insects, and tunicates, are emerging as promising options. A recent study, published by researchers from the University of Thessaly, Nofima AS, the Hellenic Center for Marine Research, and the University of Patras, among other organizations, evaluated whether an innovative combination of these ingredients could completely replace fishmeal and fish oil in the diet of the gilt-head bream (Sparus aurata), one of the most important fish in Mediterranean aquaculture. The results are encouraging: total replacement is possible without compromising growth performance, provided that a balanced mixture of these novel ingredients is used.
How was the study conducted?
The 65-day study, published in the journal Aquaculture Nutrition, was conducted with juvenile gilt-head bream (Sparus aurata) with an average initial weight of 6.57 grams. The fish were distributed in a recirculating aquaculture system and fed four distinct experimental diets:
- Control diet (C): Formulated with fishmeal and fish oil as the primary protein and lipid sources, simulating a commercial diet.
- 0%FMFO diet: In this diet, 100% of the fishmeal and fish oil was replaced by a blend of microalgae (Phaeodactylum tricornutum and Schizochytrium limacinum), defatted insect meal (Hermetia illucens), and tunicate meal (Ciona intestinalis).
- IM diet (Insect meal): Replaced 68.09% of the fishmeal with H. illucens meal.
- TM diet (Tunicate meal): Replaced 45.91% of the fishmeal with C. intestinalis meal.
At the end of the trial, researchers evaluated growth parameters, feed utilization, fillet composition, and various physiological and gut health indicators.
Growth performance: The blend outperforms individual ingredients
The most significant finding of the study was that fish fed the 0%FMFO diet (the complete blend of alternative ingredients) showed no significant differences in growth performance compared to the Control diet fish. Weight gain, specific growth rate (SGR), and feed conversion ratio (FCR) were statistically equivalent between these two groups.
This result starkly contrasts with the performance of diets that used a single alternative ingredient in high proportions:
- Insect meal diet (IM): Fish in this group exhibited significantly lower final weight, weight gain, and specific growth rate (SGR).
- Tunicate meal diet (TM): This group showed the poorest performance, with the lowest growth, reduced feed intake, and the highest FCR (worst efficiency) of all treatments.
These findings suggest that while a high inclusion of either insect or tunicate meal alone may not be nutritionally adequate for gilt-head bream, their combination with microalgae creates a synergy that allows for the successful and total replacement of fishmeal and fish oil.
Impact on fillet quality and composition
Nutrition affects not only growth but also the quality of the final product. In this respect, the 0%FMFO diet also proved to be a viable alternative.
Stay Always Informed
Join our communities to instantly receive the most important news, reports, and analysis from the aquaculture industry.
- Lipids and energy: The lipid and energy content in the fillets of fish fed the 0%FMFO diet was similar to the Control group. In contrast, the tunicate diet (TM) significantly reduced fillet lipid content, whereas the insect diet (IM) increased it.
- Fatty acid profile: Notably, fillets from fish that consumed the 0%FMFO diet showed an increase in beneficial fatty acids such as DHA (22:6n-3), 18:2n-6, and 18:3n-3 compared to the other groups. This is attributed to the inclusion of microalgae like Schizochytrium sp., which are known for their high DHA content.
Gut health and metabolism: A look inside the fish
The study also delved into how these diets affect the internal physiology of the gilt-head bream.
- Hepatic metabolism: Changes were observed in metabolic pathways. For instance, the tunicate diet (TM) appeared to induce greater use of carbohydrates for energy (higher glycolytic potential) and, interestingly, a reduction in stress response indicators (Hsp70 and Hsp90).
- Intestinal microbiome: Analysis of bacterial communities in the mid-gut revealed the presence of beneficial taxa in all groups, many of which are involved in producing enzymes, vitamins, and short-chain fatty acids. It is noteworthy that the TM diet, despite its poor growth performance, generated the greatest richness of intestinal bacteria.
- Histology: No severe alterations were detected in the liver or intestine in any of the groups. All fish, including those on the replacement diets, displayed a normal intestinal structure. A slight accumulation of lipid droplets was observed in the livers of all groups, including the Control and replacement diets.
Conclusions and implications for aquaculture
This study opens new and promising avenues for feed formulation for gilt-head bream, demonstrating that:
- Total replacement is possible: It is feasible to replace 100% of fishmeal and fish oil in diets for Sparus aurata without negatively affecting growth or feed efficiency.
- The key is in the blend: Success lies not in a single “miracle” ingredient but in a strategic and balanced combination of low-trophic-level sources like microalgae, insect meal, and tunicate meal.
- Sustainability and functionality: The use of these sustainably cultivable ingredients not only reduces dependence on marine resources but can also provide functional benefits, such as enhancing the fatty acid profile of the fillet.
These findings represent a significant step toward developing more sustainable and resilient feeds for the aquaculture industry, in line with the principles of the circular economy.
Contact
Anna Tampou
Department of Ichthyology and Aquatic Environment, School of Agricultural Sciences, University of Thessaly
GR-38446, Volos, Greece.
Email: tampou@uth.gr
Reference (open access)
Tampou, Anna, Kousoulaki, Katerina, Vasilaki, Antigoni, Vlahos, Nikolaos, Nikouli, Eleni, Panteli, Nikolas, Feidantsis, Konstantinos, Kormas, Konstantinos, Andreopoulou, Styliani, Karapanagiotidis, Ioannis T., Berillis, Panagiotis, Nengas, Ioannis, Antonopoulou, Efthimia, Mente, Eleni, Growth Performance of Gilthead Sea Bream (Sparus aurata) Fed Low Fish Meal Diets With an Innovative Mixture of Low Trophic Ingredients, Aquaculture Nutrition, 2025, 7504207, 21 pages, 2025. https://doi.org/10.1155/anu/7504207
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.
