Introduction
The sea urchin Paracentrotus lividus is an echinoderm widely distributed along the coasts of the Mediterranean Sea and the eastern Atlantic Ocean, extending northward to Ireland. This species is harvested for its gonads (roe), which are highly valued as a seafood delicacy in many European cuisines. However, increasing demand for roe, combined with overfishing, climate change, and pollution, has led to a progressive decline in natural stocks over recent decades. In response, several countries, including Italy, have implemented management measures for sea urchin fisheries at both national and regional levels. In this context, the development of echinoculture represents a promising strategy to mitigate overexploitation through restocking initiatives, while also providing a sustainable supply of biomass for the market. To advance knowledge on diet formulation and its suitability for echinoculture - currently the main constraint limiting the development of this practice, this study investigates the effects of experimental feeding regimes. Specifically, the green algae Ulva spp. (class Ulvophyceae) was selected as the primary substrate due to its sustainability, low cost, and wide availability in many coastal lagoons (Addis et al., 2023). In addition, meal derived from the black soldier fly, Hermetia illucens, was included as an alternative protein source; insect-based meals have recently been authorized in Europe as feed ingredients in aquaculture (EPRS, 2024).
The aim of this study is to evaluate the effects of two experimental diets on gonadal growth and quality, assessed in terms of color, carotenoid profile, and bioaccessibility.
Material and Methods
Trials were carried out at the research facility GillaLab (University of Cagliari, Home - GillaLab). Sea urchins (n= 240) were fed with two experimental pellet diets 1) the green seaweed Ulva spp. (UL) and 2) Ulva spp. supplemented with Hermetia illusens meal (IN). These treatments were compared with control groups: sea urchins reared in land-based tanks and fed with fresh biomass (CT), wild sea urchins (SI), and sea urchins reared in open-sea cages (SS). Gonadal growth was assessed using the gonadosomatic index (GSI), while gonad color was measured using a CIELAB colorimetric system L* =lightness, a* =red/green and b* = yellow/blue (Chroma meter CR-410, Konica Minolta Sensing, Inc., Tokyo, Japan). Carotenoid profiles were determined by chromatographic analysis and in vitro digestion (INFOGEST 2.0 protocol) was applied to assess carotenoid bioaccessibility (Brodkorb et al. 2019). The experiment lasted 30 days.
Results and Discussion
The highest GSI values were observed in SS (7.42 ± 1.97) and IN (4.77 ± 1.65), followed by CT (3.91 ± 1.03), UL (3.04 ± 0.81), and SI (2.79 ± 0.84). The ��E*ab index represents the comprehensive color difference between two samples in the CIELAB color space. Color variation among gonad samples were determined with SS as the reference. Gonads from UL and IN groups showed color parameters comparable to wild specimens, with low chromatic differences (��E*ab = 6.70 and 7.20, respectively), indicating acceptable visual quality. Carotenoid analysis revealed lutein, echinenone, and amauroxanthin as the main compounds, with significant variability among treatments. Higher lutein concentrations were found in the CT (10.93 ± 0.65 µg/g) and SS (8.29 ± 0.38 µg/g), while UL and IN, showed the lower levels (4.44 ± 0.28 and 4.07 ± 0.24 µg/g, respectively).
The INFOGEST 2.0 protocol highlighted how the bioaccessibility values ������(%) of IN sea urchin for lutein and echinenone were generally higher compared to those observed in UL and CT.
Figure 1. Colour model of gonad samples from the different experimental groups (CT, UL, IN, SS and SI). L*, a*, b* values, as well as RGB and HEX codes, are reported.
Figure 2. Gonad-somatic index (GSI, %) of (CT, UL, IN, SS and SI). Data are expressed as mean ± standard deviation.
Overall, although experimental diets resulted in lower carotenoid content, they produced gonads with colour characteristics similar to wild individuals, suggesting their potential suitability for echinoculture. The inclusion of insect meals improved gonadal growth, highlighting a promising strategy for sustainable feed formulation.
Acknowledgment
This work was supported by the Italian National Recovery and Resilience Plan (PNRR) through the project "EMBRC UP – EMBRC Unlocking the Potential for Health and Food from the Seas" (Project Code: MIUR IR0000035).
References
Addis, P., Pasquini, V., Angioni, A. et al. Ulva as potential stimulant and attractant for a valuable sea urchin species: a chemosensory study. J Appl Phycol 35, 1407–1415 (2023). https://doi.org/10.1007/s10811-023-02925-0
Brodkorb, A., Egger, L., Alminger, M. et al. INFOGEST static in vitro simulation of gastrointestinal food digestion. Nat Protoc 14, 991–1014 (2019). https://doi.org/10.1038/s41596-018-0119-1
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