Formulated Diets Drive Gonadal Maturity but Reduce Larval Success in Paracentrotus lividus

Over the past few decades, demand for sea urchin roe has risen, while wild sea urchin populations have declined. This trend has increased interest in aquaculture techniques and the development of formulated feeds to support ecological restoration and research. Here, we examined the effects of a high-protein formulated feed on gonad development in Paracentrotus lividus, compared to fresh feeds (maize and spinach), across three replicated tanks. We assessed gonad maturation, gamete viability, and larval development, and developed a new histopathological index applicable to both sexes. Formulated feed significantly enhanced gonad maturation, increased gamete production, and led to heavier gonads with higher gonadosomatic indices compared to fresh feeds, which were insufficient to promote maturation within four weeks. Notably, no histological alterations were observed in the gonads. Fertilization trials showed that embryos were produced, but none reached the pluteus stage, indicating decreased embryo viability. Although the formulated feed improved gonad development, it adversely affected water quality, increasing nutrient concentrations and lowering pH. Overall, these findings suggest that high-protein formulated feeds could potentially improve aquaculture production by enhancing gonad maturation and gamete output, but additional measures may be needed to support complete larval development.