Antulio Prieto

Growth and survival of the pearl oyster Pinctada imbricata (Röding 1758) in supended and bottom culture in the Golfo de Cariaco, Venezuela

We evaluated growth and survival rates of Pinctadaimbricata in relation to environmental changes during nine months insuspended and bottom culture in the Golfo de Cariaco, Venezuela. Juveniles,measuring 13 mm in length, were cultured using two methods, (1) inSpanish-type baskets suspended at 3–4 m in depth from a longline and (2) in baskets embedded on the seabed (7–8 m indepth). At monthly intervals, we quantified mortality and took a sample ofoysters to determine shell length (dorsal-ventral axis) and the dry mass of theshell, muscle and remaining tissues. We also quantified the dry mass of foulingon the shells (a potentially important environmental factor). Survival rateswere slightly higher in suspended culture (98–100%), although notsignificantly higher than on the bottom. The growth rate was higher in suspendedculture than on the bottom culture, and the difference between culture methodswas greater for tissue and shell biomass than for shell dimensions. At the endof the study, oysters measured 55 mm in shell length for oysters insuspension and 45 mm for those on the bottom. Although growth wasnot significantly correlated with any environmental factor, it tended toincrease with increases in chlorophyll a during periods ofupwelling, thus suggesting that phytoplankton abundance enhanced the growth ofPinctada imbricata. The pearl oyster Pinctadaimbricata should be an excellent species for aquaculture activities,given its high rates of growth and survival in suspended culture and itseconomic importance in the Caribbean region.

RELATION OF SEASONAL CHANGES IN THE MASS OF THE GONAD AND SOMATIC TISSUES OF THE ZEBRA ARK SHELL ARCA ZEBRA TO ENVIRONMENTAL FACTORS

Abstract Over the period from June 2002 to June 2003, we examined the relationship of seasonal changes in the mass of the gonad and somatic tissues to environmental factors for four size groups of the zebra ark shell Arca zebra at Chacopata, in northeastern Venezuela. The gonads of A. zebra began to increase in size when individuals attained 18–20 mm in shell length, but maximum gonad mass relative to somatic mass was only attained at 55–60 mm in length. Large individuals (>50 mm) showed a distinct annual reproductive cycle with a marked increase in gonad mass from July to late September 2002, coinciding with the increase in temperatures related to stratification of the water column. A decrease in gonad size occurred during October 2002 through January 2003 and coincided with a temperature decline related to renewed upwelling. The mass of somatic tissues was highest between late August to late December 2002, coinciding with the reproductive period and elevated temperatures. Other environmental factors showed little seasonal variation, although chlorophyll a concentration was lowest during the major period of increase in the gonad and somatic tissues (July to late September 2002), suggesting that the animals were not limited by the abundance of phytoplankton food. A. zebra seemed to be well adapted to the high loads of inorganic seston found in the Chacopata region.