Temporal changes in sex-specific color attributes and carotenoid concentration in the gonads (roe) of the purple sea urchin (Paracentrotus lividus) provided dry feeds supplemented with β-carotene

Abstract

The market value of sea urchin roe (female and male gonads) depends on several quality criteria, such as size, color, texture, and flavor. Sea urchins given dry pellet feed often produce large gonads, but the preferred bright orange color has been difficult to achieve without the inclusion of supplementary dietary carotenoids. Gonad color depends on carotenoid concentrations (CC), and is influenced by several factors, including diet and sea urchin sex. This study aimed to evaluate the impact of sea urchin sex, gonad size, and maturation level on gonad color and CC. Small Paracentrotus lividus urchins (18 mm test diameter) were fed every 48 h with three diets of similar proximate composition (protein: 31–33% dry matter DM, fat: 9–10% DM; carbohydrates: 45–46% DM). The diets were formulated with fishmeal, algae, and plant-based ingredients and supplemented with β-carotene (100 mg Kg−1). The nutritional trial was conducted in three recirculatory aquatic systems equipped with 40 L glass tanks guaranteeing triplicates by diet with an initial biomass of 5 g L−1. The gonadosomatic index (GSI), gonad maturity and color of 15 urchins per replica were analyzed at mid-trial (103 days, T1) and at the end of the trial (173 days, T2), and compare with initial condition (baseline). At each sampling event, the color of female (F) and male (M) gonads was analyzed using qualitative (four-level visual scale) and quantitative methods (Commission Internationale de l’ Eclairage CIE L*, a* and b* color parameters). Additionally, CC was determined by spectrophotometry in pooled samples freeze-dried gonads per replica and sex and compared with baseline. At T1, 59 females and 71 males were analyzed, and results showed that females presented larger (GSI = 7.50) gonads with higher CC (117.5 μg g−1 DM) than males (GSI = 5.16 and CC = 76 μg g−1). Female gonads also presented a more intense color (a* = 8.8, b* = 17.13) than males (a* = 5.1, b* = 12.49). At T2, 61 females and 62 males were analyzed and, except for a high percentage of female gonads classified as color grade I (57%), the differences on gonad color and CC between sexes identified in T1 became non-significant. In general, the gonad color tended to become lighter (L*, baseline: 34.8 and T2: 47.2) and yellower (b*, baseline: 12.5 and T2: 17.50), and CC decreased (baseline: 201.8 μg g−1 DM and T2: 31.6 μg g−1 DM) with increasing gonad weight (baseline: 0.16 g and T2: 0.77 g) and GSI (baseline: 3.0% and T2: 9.9%). In conclusion, this study shows that the carotenoid concentration and color attributes of sea urchin gonads are influenced by sea urchin sex and gonad size. The different diets and the carotene supplementation had little or no effect on the gonad CC and color attributes, indicating that the sources and concentrations of carotenoids in the diets were not sufficient to allow the accumulation of pigments in the gonads needed to enhance the color of P. lividus urchins.