In recent decades, various species of Mediterranean sea urchins, including Paracentrotus lividus, have been subject to widespread seasonal episodes of mass mortality whose causative agents are still unclear. In particular, P. lividus is subject to late winter events of mortality, due to a disease manifested by a massive loss of spines and the presence of greenish amorphous material on the tests (i.e., the sea urchin skeleton consisting of spongeous calcite). Documented mortality events show a seasonal epidemic diffusion and might produce economic losses also in aquaculture facilities, besides the environmental constraints to its diffusion. We collected individuals showing conspicuous lesions on the body surface and reared them in recirculated aquaria. Samples of external mucous were collected along with coelomic liquids and cultured to isolate bacterial and fungal strains, further submitted to molecular identification through the amplification of prokaryotic 16S rDNA. In addition, pools of infected sea urchins were reared in recirculated tanks after short baths in a formulated therapeutic compound and their survival rates were compared to non-treated individuals for variable periods. Here, we aimed at a redescription of the etiopathogenetic nature of the parasites and tested the efficacy of a possible treatment, to be proposed for aquaculture purposes.

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.