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RESEARCH PRODUCT

Exploitation of food processing discards as main ingredients of sustainable feeds for the aquaculture of Paracentrotus lividus

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Sea urchin gonads are considered a delicacy in many parts of the world, leading to an increase of fishing pressure and resulting in the decline of natural stock of commercially valuable species. Aquaculture could be the best solution to fill the gap between market demand and natural supply, but in a context of Sustainable Development and Blue Growth, aquaculture sector is called to reduce its ecological footprint. Aquaculture feeds are produced using ingredients obtained from natural resources already overexploited by human activities, such as fish meal and fish oil that are considered the best source of lipids, or cereal meals that are included as protein sources. In this context, in order to propose a more sustainable approach, increasing attention has been focused on the formulation of alternative feeds, with low environmental and economic impacts, for the two main field of sea urchin aquaculture: gonad enhancement of wild specimens and full-cycle production, from larval development until the achievement of the commercial size. Here, sustainable diets obtained using food processing discards as main ingredients were produced and tested as feed for the purple sea urchin Paracentrotus lividus (Lamarck, 1816), the most important commercial sea urchin in the Mediterranean Sea. A first short-term feeding experiment was conducted to assess feed stability in seawater, testing two different amounts of binder on formulated feed. The nutritional value of the main ingredients and feed formulations was assessed, and then a bioenergetics trial was conducted to test feed suitability for P. lividus. Findings confirmed the goodness of the proposed formulations for sea urchins, due to their satisfactory stability in seawater, palatability and adequate nutritional value. In the next step, two of the four proposed formulations tested in the previous experiment, were selected to feed adult P. lividus for three months, aiming to evaluate gonad development, biomass increase and quality. Results highlighted a progression in sea urchin sexual maturation and a significant rise in gonad biomass coupled with a consistent increase of the gonad somatic index. Finally, sea urchins fed with the experimental feed formulations presented high quality gonads, thanks to a marketable colouration. A third long-term feeding experiment was conducted on adult females of P. lividus reared using five diets: four composed mainly of lettuce discards and one composed of macroalgae, considered their natural food. Diet performance was evaluated employing a new productive protocol, the Raking method, which allows testing the effects of experimental diets on egg production rather than in gonad production, without sacrificing the experimental sea urchins. Thus, ingestion, absorption efficiency, somatic growth, egg production and quality were assessed to evaluate the suitability of the five 5 experimental diets. Findings showed that the lettuce-based diets resulted more effective than algal diet, presenting an adequate nutritional content, promoting increase in total weight and egg production, and presenting a better egg colour. Finally, the effect of the five experimental diets on larval development was assessed, using stable isotope and fatty acid analyses to secure dietary nutrient allocation in produced eggs, with the aim to extend the information of nutrient needs for the development of a full cycle production system. Results of SIA and FA confirm diet assimilation, with significant changes in egg composition according with the respective diet. The analysis on larval development showed a lower efficacy of lettuce-based diets than the algal diet, which promoted a faster and more efficient larval development. The three experiments allowed a comprehensive evaluation of the validity of sustainable diets and feeds for P. lividus, presenting encouraging results. Findings suggest that the nutritional content of the diets used allows the production of gonads of adequate size and quality to meet market demands, thus making them suitable for the practice of gonad enhancing. On the other hand, they do not seem to meet the correct composition to produce gametes able to sustain effective and complete larval development.