EUROPEAN SEABASS AND GILTHEAD SEABREAM REQUIRE TAILORED MICRODIETS FOR FIRST FEEDING

Introduction and Aim

Early larval nutrition remains one of the main bottlenecks in marine fish aquaculture, strongly influencing survival, growth, robustness and juvenile quality. Recent advances in inert microdiet technology aim to reduce reliance on live feeds while improving nutritional precision and sustainability, including the use of novel ingredients such as algae-derived components and protein hydrolisates. This work synthesises results from four controlled feeding trials evaluating innovative microdiets during first-feeding and early weaning of two important Mediterranean aquaculture species: gilthead seabream (Sparus aurata) and European seabass (Dicentrarchus labrax). The overall aim was to assess how dietary formulation and feed processing innovations can enhance larval performance, thereby supporting the development of effective alternatives to live prey in hatcheries.

Experimental design

Trials were performed at IPMA (Portugal) facilities. Larvae were reared in 300 L cylindro-conical tanks (open circulation, 36‰ salinity) under controlled conditions. Seabass were kept at 16.5 ± 1 °C and offered experimental microdiets starting at 8 or 15 days after hatching (DAH) (depending on the trial) through to 50 DAH, under a co-feeding regime with live prey. Seabream were kept at 18 ± 1 °C, with microdiets introduced at 2 or 3 DAH (depending on trial) through to 50 DAH, also in co-feeding with live feed. Dietary treatments in these trials targeted variations in feed formulation — such as peptide hydrolysis level (producing different average peptide sizes), inclusion level of marine protein ingredients, and inclusion of algal fractions — as well as feed processing technology (fluidized bed agglomeration vs. micro-extrusion). Each trial monitored key performance indicators including larval growth (length and dry weight), survival, and incidence of skeletal deformities.

Results and Discussion

Across all trials and for both species, the novel microdiets produced by fluidized bed agglomeration (FBA) supported good larval performance, in some cases matching or even exceeding the growth achieved with reference diets produced by standard micro-extrusion. No significant differences in survival or in the incidence of skeletal deformities were observed among dietary treatments within each trial. However, clear species-specific responses to diet were evident. In seabream larvae, diets formulated with larger peptide fractions consistently promoted greater larval length and dry weight compared to diets with more extensively hydrolysed (smaller) peptides. In contrast, seabass larvae showed an opposite trend: at an early stage (22 DAH), a diet containing smaller peptides resulted in improved growth relative to the control, but by the end of the nursery phase (50 DAH) this same diet led to depressed growth performance.

Figure 1. Infographic summarizing Algae Vertical findings on how dietary formulation and feed processing innovations can enhance first feeding larval performance.

Conclusions

The optimal level and type of marine protein ingredients for maximizing growth differed between gilhead seabream and European seabass. Nonetheless, increased inclusion of algal ingredients (such as microalgae-derived components) yielded good growth in both seabream and seabass, indicating the potential of these sustainable ingredients in larval diets. Overall, these results demonstrate major progress in first-feeding strategies for marine fish, driven by advances in microdiet formulation and production technology and by the use of alternative ingredients (including algae). Crucially, the data show that optimal diet characteristics differ markedly between fish species, and even between developmental stages within a species, indicating that a "one-diet-fits-all" approach is not appropriate. Tailored, species-specific microdiets are therefore essential to maximize larval performance and quality in order to support aquaculture sustainability.

Acknowledgments

This work was financially supported by "Pacto da Bioeconomia Azul" (Project No. C644915664-00000026) within the WP5 Algae Vertical, funded by Next Generation EU European Fund and the Portuguese Recovery and Resilience Plan (PRR), under the scope of the incentive line "Agendas for Business Innovation" through the funding scheme C5 – Capitalization and Business Innovation. Technical support from EPPO and S2AQUAcoLAB staff, as well as the SPAROS feed production team, is gratefully acknowledged.