Changes in shell dimensions of pearl oysters, Pinctada mazatlanica (Hanley 1856) and Pteria sterna (Gould 1851), during growth as criteria for Mabé pearl implants

The relationship between the shell dimensions of pearl oysters. Pinctada mazatlanica (Hanley 1856) and Pteria sterna (Gould 1851). was studied to determine the possible change of form of the shell during growth. The intention was to determine the number, size and location of nuclei that could be implanted in oysters used for Mabé pearl production. Using the database of our Pearl Culture Research Programme developed in Bahía de La Paz, México, we obtained measurements of 500 shells of P. mazatlanica and 500 shells of P. sterna, representing 3 years of continuous growth under extensive culture conditions. The height-length, height-thickness and the height-weight relationships of both species were analysed, as was the height-wing length relationship for P. sterna. There was isometric growth up to 100 mm shell height, and negative-allometric growth after 120-125 mm for P. mazatlanica. The height-thickness relationship followed a linear model, whereas the height-weight relationship was exponential. No clear allometric pattern was found in P. sterna and all relationships fitted the power equation.     

Spatfall of pearl oyster, Pteria sterna (Gould), on experimental collectors at Bahía de La Paz, South Baja California, Mexico

Spatfall of pearl oyster, Pteria sterna (Gould), was analysed at two sites, stations Gaviota and Merito, at Bahía de La Paz, South Baja California, Mexico, during an annual cycle in 1991-1992. and from surface to 15 m depth. Sampling was carried out monthly using experimental collectors which remained immersed for 60-65 days. Four different substrates were tested for spat settlement preference: a native bush called ‘chivato’, dry palm leaves, and red and yellow plastic onion bags: temporal variations, and horizontal and vertical spatfall distribution patterns were evaluated between and within stations. Spat settlement showed significant differences depending on the structure and texture of the substrate type. Chivato bush was in general the best spat collector, but was difficult to handle for large-scale operations; plastic onion bags were more suitable and spat yield was adequate; palm leaves were poor spat collectors. There was no evidence for colour preference of spat settlement between red and yellow onion bags. Pteria sterna spat were present throughout almost all of the study period. Main spatfall was detected in winter-spring, coinciding with low temperatures; most spat then occurred from surface to 4-5 m depth. Few spat were present in summer and most then occurred below 7-9 m depth. The distribution patterns of spat within substrate replicates were apparently influenced by the abundance of spatfall. Aggregated spatial patterns were evident in shallow water during months of maximum spatfall but not when spat was less abundant. These events did not occur in the same substrate type, and differences were also detected between stations. Trends were related to oceanographic conditions prevailing at each site. Two patterns of spatfall abundance and vertical distribution were evident, one for winter-spring, and the other for summer. Samples at station Gaviota were grouped by spatfall abundance and spat vertical distribution patterns, while the latter defined better the grouping of samples at station Merito. Geographical variations of spatfall characteristics for Pteria sterna itself, and in comparison with Pinctada mazatlanka (Hanley) in the Gulf of California, are discussed.     

Growth of the Pearl Oysters Pinctada mazatlanica and Pteria sterna in Different Culture Structures at La Paz Bay, Baja California Sur, México

A growth study of Pinctada mazatlanica and Pteria sterna was conducted to explain the basic steps required for the development of a pearl culture program in México. Seed for both species was collected using onion bags filled with black polyethylene sheets (40 ± 80 cm) and 5 g of vexar filament. The spatfall was July-August 1987 for P. mazatlanica and December 1987-February 1988 for P. sterna . The seed (12.8 ± 1.2 and 13.0 ± 0.6 mm respectively) was placed in pearl-nets for intermediate culture (to attain 30 mm height). Populations were subsequently divided into three groups, two groups at 10 m depth in lantern and pocket nets and a third placed over a submerged shelf at 10 m depth in plastic net cages. Growth in height, survival and temperature were monitored. After 22 mo P. mazatlanica showed no significant differences in growth between culture structures. Nevertheless, the survival obtained in cages (99%) was larger than that obtained in hanging structures (65%). After 18 mo of culture, significant differences (F = 5.199 P = 0.05) in growth were observed for P. sterna . Larger animals were found in pockets (106.6 ± 0.8 mm) followed by lanterns (104.0 ± 0.7 mm) and finally in cages (103.5 ± 0.6 mm). Survival in pockets was 99%, 84% in lanterns and 98% in cages. With the operation of the different culture structures used in this study, the bottom cage system seems optimal to begin a culture program to obtain pearl-oysters for nucleus implantation.     

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

The Calafia mother‐of‐pearl oyster, Pinctada mazatlanica (Hanley), and the Rainbow nacre shell, Pteria sterna (Gould), represent an important resource for México because of their potential in pearl production. The present work deals with the effect of different sequences of nursery culture‐late culture on growth and survival of P. mazatlanica, from September 1993 to October 1994. The collected spat presented two main size groups: small (mean shell height of 7 mm), and large (13 mm). They were arranged into four experimental batches for each size group at a constant stocking density of 40–45 juvenile pearl oysters per Nestier cage. Three batches remained in nursery culture 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 weight (g), data of shell volume (height × width × depth, in mm³) was also introduced to estimate and compare growth among the experimental groups. Mortality was estimated by counting the dead specimens every month and obtaining the percentage from a 100% initial survival at the start of the experiment. The juveniles showed different responses to the change from nursery culture to late culture; the level of each response varied significantly among the experimental groups at the end of the study. It seemed that a 6‐month period for nursery culture was propitious for P. mazatlanica.     

Growth and survival of the winged pearl oyster Pteria sterna (Gould, 1851) in suspended culture in the tropical Eastern Pacific: Influence of environmental factors

The growth, survival and influence of environmental factors were analysed in two cohorts of cultured Pteria sterna in Ayangue Bay, Province of Santa Elena, Ecuador (tropical Eastern Pacific). Juveniles representing cohorts I and II (8.4 ± 0.54 and 5.0 ± 0.17 mm in dorso‐ventral axis) were deployed in November 2015 and February 2016, and grown in pearl nets suspended in a long line for 12 and 10 months respectively. The stocking density was monthly and bi‐monthly reduced during sampling of individuals to determine growth in dorso‐ventral shell axis, dry mass of shell, soft tissues and dry mass of fouling on shell. Water temperature, salinity, total seston and phytoplankton biomass (chlorophyll a) were determined at the culture site. Results showed that P. sterna reached ~100 mm in length during the first year of culture. Although little negative influence of environmental factors was detected, high temperatures during the reproduction period can be the most negative influential trait. The highest tissue mass (6 g), which occurred at the 10th month of cultivation, as well as a high availability of spat by artificial collectors in the coastal waters, showed that the species can be considered a good candidate for aquaculture in the tropical eastern Pacific.     

Results of spontaneous spawning of yellow snapper (Lutjanus argentiventris peters, 1869) reared in inland ponds in La Paz, Baja California Sur, México

Maturation and fecundity in two-year cycle of the yellow snapper (Lutjanus argentiventris) was studied as a potential fish-culture species in northwest Mexico. The results of this work will be used in future experiments to control sexual maturation by manipulation of photoperiod and temperature.     

Mortality, growth and somatic secondary production of the bivalve, Pinna rugosa (sowerby), in suspended and bottom culture in Bahia de La Paz, Mexico

The objectives of this study were the determination of mortality, growth, condition factor and meat yield, biochemical variables, and somatic secondary production of Pinna rugosa (Sowerby, 1835) in suspended and bottom conditions in Bahia de La Paz, Mexico. The use of each of these parameters was analysed as a decision element for managing the resource. The experimental design was based on the recruitment of wild spat on collectors and introducing bivalves of the same size into different areas. In each area, bivalve samples were used both in suspended trays, and lying on the bottom, approximating their natural occurrence, but surrounded by a plastic mesh fence. The stocking densities in both cultivation systems were 50, 100 and 150 m^?2. The organisms were checked monthly for almost 2 years, recording various measurements. In one of the treatments that most closely represented the average, the growth values were 19.5 mm month^?1 and 14.5 g month^?1 in the first year, a length-growth Von Bertalanffy K of 0.118 and an instantaneus growth rate in weight G of 4.77. During the first year, there was annual mortality of 22% on the bottom and 11% at the surface, with somatic secondary production, in dry weight, of 17.8 g per organism. The results of the estimation of each variable were submitted to a multifactorial anova . NO significant differences in K as a function of sites, cultivation systems or density could be found. The effect of site on instantaneous growth rate G was significant. The largest values were from the inner bay (site 1) where the highest mortality rate also occurred. Among condition factor, meat yield and biochemical components, only lipids showed a difference for systems and site factors. We concluded that secondary production gave statistical elements for the selection and culture decision-making in all factors tested. The results showed good aquaculture prospects for P. rugosa.