FISHERIES RESEARCH INSTITUTE,MOA,TAIWAN

The top shell, Tectus pyramis, is one of the most heavily exploited marine gastropods in the Penghu area, Taiwan. Experiments on induced spawning of this species were conducted in this study to establish a technique for mass seed production and stock enhancement. Mature shells were collected from the Penghu area. The effects of temperature, desiccation, and their combination on induction of spawning were studied. Results showed that the 3 methods were significantly effective at induced spawning. The combined method had no significant extra effect as compared to the other 2 methods. Fertilized eggs of the top shell are granular, spherical, green, and demersal, with a mean diameter of 252.0 ± 4.8 µm. The first cleavage occurred at about 40 min after fertilization at a water temperature of 27.1 °C. The second cleavage occurred at 60 min, and the third cleavage occurred at 80 min after fertilization. In the third cleavage, there were 4 bigger, white cells at the vegetable pole, whereas there were 4 small, green cells at the animal pole. The cells in both the vegetable and animal poles individually symmetrically cleaved. Prototrochal cilia appeared at 4 h and 50 min, and the trochophore stage developed at 8 h and 40 min. The formation of the larval shell in the veliger stage was at 17 h and 40 min. Metamorphosis to become a crawling larva occurred at 35 h.