Embryonic Development and Larval Rearing of the Topshell Trochus niloticus (Linnaeus)

The topshell Trochus niloticus is an economically important species due to its high nutritional value and ecological significance. However, wild populations have declined sharply due to overharvesting and habitat degradation. Current breeding efforts remain fragmented, with low reproducibility and limited investigation into optimal food sources. In addition, conventional methods for defining developmental stages lack precision, thereby limiting the development and application of technologies for accurate cultivation management. In this study, artificial breeding was investigated by optimizing induced spawning techniques, systematically documenting morphological changes during embryonic development, and comparing the effects of different algal diets to advance the aquaculture industry for T. niloticus. Spawning was successfully induced through a combined approach involving desiccation and water-exchange stimulation. The embryonic developmental process was carefully documented and categorized into the following sequential stages: the intra-egg membrane development stage (0–11 h), the protoconch larval stage (11–36 h), the metamorphosis stage (36 h–4 d), the ‘white-shell’ stage (48 h–15 d), and the ‘green-shell’ stage (beyond 15 d). Among the three feeding regimes evaluated, larvae fed benthic diatoms exhibited relatively faster growth and development. T. niloticus displayed an initial slow-growth phase during the first three months, followed by a period of accelerated growth, and a significant positive correlation was observed between shell length and shell weight in juveniles. This study established a comprehensive technical protocol encompassing broodstock spawning induction through juvenile rearing. It also provides critical developmental timelines and morphological indicators during the transition from embryo to juvenile. Collectively, these findings establish a theoretical foundation for the large-scale seed production of this species.