Growth and survival of the Calafia mother-of-pearl oyster Pinctada mazatlanica (Hanley 1856) under different sequences of nursery culture-late culture at Bahia de La Paz, Baja California Sur, Mexico

The Calafia mother-of-pearl oyster, Pinctada mazatlanica (Hanley), and the Rainbow nacre shell, Pteria sterna (Gould), represent an important resource for Mexico because of their potential in pearl production. The present wor k deals with the effect of different sequences of nursery culture-late cult ure on growth and survival of P. mazatlanica, from September 1993 to Octobe r 1994. The collected spat presented two main size groups: small (mean shel l height of 7 mm), and large (13 mm). They were arranged into four experime ntal batches for each size group at a constant stocking density of 40-45 ju venile pearl oysters per Nestier cage. Three batches remained in nursery cu lture for 2, 4 and 6 months respectively, after which they were transferred to late culture in rail cages. A control group remained in nursery culture for 12 months. Growth was evaluated monthly and compared through anova and HSD Tukey tests. In addition to the shell height, width, depth (mm) and we ight (g), data of shell volume (height x width x depth, in mm(3)) was also introduced to estimate and compare growth among the experimental groups. Mo rtality was estimated by counting the dead specimens every month and obtain ing the percentage from a 100% initial survival at the start of the experim ent. The juveniles showed different responses to the change from nursery cu lture to late culture; the level of each response varied significantly amon g the experimental groups at the end of the study. It seemed that a 6-month period for nursery culture was propitious for P. mazatlanica.