Biologia

REPRODUCTION AND LARVAL DEVELOPMENT OF THE
WEST INDIAN TOPSHELL, CITTARIUM PICA
(TROCHIDAE), IN THE BAHAMAS

Lori J. Bell

ABSTRACT

The reproduction and larval development of the West Indian topshell, Cittarium pica (Linnaeus), was studied in the southern Exuma Cays, Bahamas, between June 1990 and June1991. Topshells held in outdoor water tables spawned unpredictably, possibly inresponse to simulated low and high tides and the moon phase. Eight of nine spontaneous spawnings occurred within 4 days of either the full or new moon between 20 June and 4 November.

Larvae of C. pica were lecithotrophic with a relatively short larval life of 3.5-4.5 d, when reared at 26.5-27.5·C. Emergence from the egg membrane occurred at the trochophore stage. At this stage the larval shell coveredabout two-thirds to three-fourths of the posterior end of the larvae, with the velum not yet developed. Settlement could be induced by providing a bacterial/algal film substratum. Oocyte diameters from histological slides of ovaries were used to determine reproductive seasonality. Females began to mature in July.

A gradual increase in oocyte diameters occurred over the summer until theypeaked in late September and early October, followed by a significant decline. Oocyte size was variable between October and January, after which the mean size was consistently small with little variability. The data suggest a natural spawning period in early October. Mean oocyte diameter was highly correlated with seawater temperature. An influx of juvenile C. pica (1-2 mm shell width) was observed inJanuary. Using growth rates of laboratory-reared juvenile C. pica, a spawning date corresponding to the significant decline in oocyte diameter in early October was extrapolated.

The West Indian topshell, Cittarium pica (Linnaeus, 1758) (Trochidae), is an intertidal gastropod found along rocky shores in the Bahamas and Caribbean, south to Trinidad (Abbott, 1974). It is very rare in south Florida(Abbott, 1976) and became extinct in Bermuda in comparatively recent times (probably early 1800's, Verrill, 1901). It is an important food item, second only to the queen conch, Strombus gigas, in value among Caribbean gastropods (Randall, 1964; Flores and Talarico, 1981), and it has been overexploited in many of the dense1ypopulated areas of the West Indies (e.g., Cayman Islands, P. Bush, pers.comm.; Virgin Islands, R. Boulon, pers. comm.; Venezuela, Flores and Talarico, 1981). The biology of C. pica was first studied in the Virgin Islands by Randall (1964). More recently Castell (1987) and Debrot (1990a; 1990b) studied various aspects of its biology. Aside from seasonal trends in gonad indices (Castell, 1987; Debrot, 1990a), little is known of the reproductive activity of C. picaTrochids are found in tropical and temperate waters and the reproductive cycles of temperate intertidal trochids have been fairly well documented (Fretter and Graham, 1977; Garwood and Kendall, 1985; Lasiak, 1987). Colman and Tyler (1988) have provided the first insight into the reproduction of a deep-sea (990-2,450 m) trochid. Spawning in the laboratory, as well as larval development, has beendescribed for several temperate species (Desai, 1966; Underwood, 1972; Holyoak, 1988a; 1988b). Much less is known about reproduction of tropical trochid gastropods. Spawning and larval development offive tropical species have been described from the Pacific and Red Sea (Gohar and Eisawy, 1963; Duch, 1969; Eisawy, 1970; Heslinga, 1981; Hulings, 1986), although little has been reported of their reproductiveperiodicity (Randall, 1964; Heslinga and Hillmann, 1981).

The objectives of the present study were to describe and illustrate the larval development of C. pica and to examine aspects of its reproductive periodicity. This information could be applied to management and possible mariculture of the species.

MATERIALS AND METHODS

This study was conducted from June 1990 through June 1991 at...