Advancements in controlled reproduction of the endangered species Pinna nobilis, comparing spontaneous and controlled fertilization on the larval development

Abstract

In response to the critical decline of Pinna nobilis populations in the Mediterranean, following a multifactorial disease outbreak that caused mass mortality, several conservation efforts were initiated to safeguard surviving populations, including the reintroduction of juvenile and adult P. nobilis. Aquaculture was identified as a valuable conservation strategy to support captive reproduction while reducing pressure on wild populations. Central to these efforts is a comprehensive understanding of reproductive biology and the development of rearing protocols in controlled environments. To this end, a specific aquaculture set-up was used to improve the maintenance conditions of P. nobilis in captivity. Five spawning induction assays were performed on 6 adults between May and July 2024 by thermal shock. An additional two spawning events were triggered by transport stress, providing the release of only male gametes and already dividing oocytes (putative self-fertilization). Low larval viability was observed in these latter events, since larvae stopped at the D-larval stage (9 days post-fertilization-dpf). Following the thermal shock, we observed the release of male and female gametes (unfertilized eggs), separately, by several specimens, enabling controlled fertilization, resulting in larval development that reached the umbonate larval stage (150 μm, 16 days post fertilization). This last larval cycle lasted up to 21 days (although the larvae died afterwards), in contrast to spontaneous internal fertilization. This success was likely due to a combination of factors: larval density (5 embryos/mL), water changes every two days, and a diet rich in EPA (eicosapentaenoic acid). Collectively, these elements underline the potential of controlled aquaculture systems to support the early development and conservation of P. nobilis.

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