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To improve the sustainability of aquaculture practices, a step towards the use of alternative nutrient sources (such as food processing discards) may secure the future of aquaculture sector, namely for emergent species, such as sea urchins. In this context, adult females of the commercial sea urchin Paracentrotus lividus were reared using four feeds based on lettuce discards (72%) and enriched (8%) with an animal-source ingredient (fish Sardina pilchardus, Feed-S; krill Euphausia superba, Feed-K; mussel Mytilus galloprovincialis, Feed-M; anchovy Engraulis encrasicolus discards, Feed-AD). A fifth feed, used as control treatment, was composed of macroalgae (Laminaria sp. and Ulva sp., Feed-UL). Feed performance was evaluated employing a new productive protocol, the Raking method, which propose testing feed effects on sea urchin caviar (oocytes rather than gonads) production. Thus, ingestion rates and absorption efficiency were measured to evaluate feed palatability. Somatic growth and caviar production, expressed introducing the ovosomatic index (OI) instead of the traditional gonadosomantic index, were measured to assess feed productive performances. Caviar quality was assessed by nutritional content and color. Ingestion rate results showed that all feeds were palatable, while findings on absorption efficiency showed differences between the five proposed feeds, with Feed-M and Feed-AD presenting the worst results. Somatic growth was promoted regardless the provided feeds, while OI resulted higher with Feed-K and Feed-M than the other feeds. All produced caviar resulted suitable for human consumption with high protein and fatty acid content, but caviar produced by Feed-UL showed the poorest nutritional profile. Similarly, Feed-UL led to the production of caviar with the lowest quality color, while Feed-S showed the best orange color. Lettuce-based feeds were therefore effective for feeding P. lividus as they stimulated production of high quality caviar. Findings support the exploitation of food discards for the production of eco-friendly feeds for sea urchin aquaculture.

Development of sustainable aquaculture practices is a suitable solution to reduce the pressure on overexploited stocks of the Mediterranean sea urchin, Paracentrotus lividus, and to respond to the increasing market demand. To move forward the Blue Growth and following the principles of circular economy, a three-month feeding experiment was conducted to test a sustainable feed based on food processing discards on sea urchins. Two feed formulations differing on the proportions of the two main ingredients (endive outermost leaves and European anchovy discards in a ratio of 60:40 and 80:20 respectively) were prepared and tested on P. lividus gonad yield, development and quality. The results were compared with those of wild sea urchins to assess the differences with natural patterns. Both feed formulations promoted gonad growth resulting in a significantly higher percentage increase in gonad biomass compared with wild specimens (490%, 330% and 78% increase in gonad weight in the feed 60/40, 80/20 and wild sea urchins respectively). Similarly, GSI of reared sea urchins varied by about 3–12% and 14% for sea urchins fed with feeds 80/20 and 60/40 respectively, while that found in wild sea urchins varied by about 3–5%. Gonad development was also boosted by the provision of the sustainable feed, as sexual maturation was faster in reared specimens than in wild ones. At the end of the trial, reared sea urchins showed also a very high (> 90%) frequency of marketable gonad colour. Lastly, the formulation with a more balanced vegetal/animal ratio (feed 60/40) gave the best results overall, combining the highest GSI and the best gonad colouration. Outcomes of this study confirm the suitability of food processing discards as ingredients for sea urchin feeds, although further research is needed to evaluate the effects on nutritional quality and organoleptic features of sea urchin gonads.