Pablo Monsalvo-Spencer

Suspension culture of catarina scallop Argopecten ventricosus (=circularis) (Sowerby II, 1842), in Bahia Magdalena, Mexico, at different densities

Abstract Hatchery-reared spat (5 mm) of catarina scallop ( Argopecten ventricosus (=circularis )) were cultured in plastic trays suspended from a long line at Rancho Bueno, Baja California Sur, Mexico. The mean surface temperature range was 20 to 29 °C and salinity remained steady at 37 ppt during the 320-day experiment. Every 1 or 2 months, the trays and the scallops were cleaned, the scallops measured, and survival recorded. Three densities were tested on each of the culture stages; called nursery (from day 1 to day 80), intermediate (80 to 136) and growout (136 to 320). Average densities were 1500, 2500, and 4000 scallops/m 2 for the nursery stage; 400, 700, and 1000 for the intermediate; and 150, 250, and 400 for the growout stages. At the end of nursery and intermediate stages, scallops of the modal size class were selected to begin the following stage using scallops of homogeneous size. In the nursery stage, growth rate was higher at low density. At the intermediate stage, growth rates were highest in low and medium densities ( P P 91% at the end of the experiment and did not correlate with density. Mortality began to occur in animals older than 8 months, during the spawning season at the onset of summer. Two hypothetical growth curves were constructed from the data taking for each stage those densities producing the fastest and slowest growth. Results indicate maximum shell length could be attained in 273 (fastest) and 398 (slowest) days. A cost analysis indicates that, regardless of the longer time, culturing scallops at high density would be less expensive than at low density, taking into account the muscle-weight loss caused by crowding.

FACTORS INFLUENCING RECRUITMENT OF HATCHERY REARED PEARL OYSTER (PINCTADA MAZATLANICA; HANLEY 1856) SPAT

Abstract We evaluated experimental collection of Pinctada mazatlanica spat on substrates of different textures and colors placed at different depths within settlement tanks. When larvae reached the pediveliger stage (day 25), black-colored spat collectors (“envelope” type) composed of the following materials were offered as settlement substrates: onion bag, mosquito net, fishing net, and 63% shade-cloth. Spat collectors measured 30 × 30 cm and were composed of an outer bag and inner substrate made of the same material. The influence of the color of spat collector material on recruitment was investigated using a second type of spat collector composed of onion bags as the outer bag and inner substrate (“bag” type). Bags were prepared in 3 different outer/inner (O/I) color combinations of green/green, green/black, and red/black (O/I). Both types of collectors were deployed at different depths within settlement tanks. Approximately 2.7% of the initial larval population survived, resulting in 35,583 spat. Of these, 71.3% recruited to bag type collectors, 21.9% to envelope type collectors, and 6.8% to the surfaces of the culture tanks. Spat recruitment was significantly affected by collector material (P < 0.01), with fishing net and shade-cloth yielding highest and lowest density of spat, respectively. Similarly, spat collector color combination significantly influenced spat collection (P < 0.01), with higher recruitment to red and green substrates. For both spat collector types, there was significantly greater (P < 0.01) recruitment of spat to collectors in the middle of the water column (60–90-cm depth). This study showed that both the type and color of material used for spat collectors, as well as depth of deployment, influenced recruitment of P. mazatlanica spat. These results will help fine-tune current hatchery techniques for this species.

Mixture of parthenogenetic and zygogenetic brine shrimp Artemia (Branchiopoda: Anostraca) in commercial cyst lots from Great Salt Lake, UT, USA

The brine shrimp Artemia is one of the most studied animals in the world. A large part of the knowledge of this crustacean is based on cysts harvested from two main sources; the Great Salt Lake, UT (GSL), and the San Francisco Bay salterns, CA (SFB), USA. Artemia populations from these habitats are recognized to belong to a single zygogenetic species, Artemia franciscana Kellogg, 1906. However, the GSL Artemia has been in doubt for more than a century about the existence of parthenogenetic reproduction. By using morphological, reproductive, and molecular analyses, we report that commercial GSL cyst lots contained two different brine shrimp species; a parthenogenetic (60%) and a zygogenetic (A. franciscana) (40%). From this finding, at least three hypotheses can be drawn. The parthenogenetic Artemia is native of GSL, or it was introduced to GSL, or foreign parthenogenetic cysts were mixed with A. franciscana cysts and canned for commercial distribution. Researchers using brine shrimp cysts from GSL should therefore pay careful attention to the correct identity of the species under study. The potential of an easy and unnoticed introduction of parthenogenetic Artemia into America is discussed.

Heavy metals in the clam Megapitaria squalida collected from wild and phosphorite mine-impacted sites in Baja California, Mexico: considerations for human health effects.

The “chocolate clam” Megapitaria squalida, is widely consumed by the population of several localities along the Pacific coast. Clams collected from seven stations in Bahía de la Paz, a bay within the Gulf of California, before and after the summer rainy season were analyzed for Pb, Ni, Cd, Mn, Zn, Cu, and Fe. The location of the sampling sites significantly affected the concentration of metals in clam tissues, but not in relation to the proximity to alleged contaminated sites. Clams from a site close to a phosphate mine had the highest levels of Pb, but only in April, and the highest concentrations of Cd were recorded in clams collected in areas with no anthropogenic activities. Clams from sites considered clean had higher levels of Cd, Fe, Zn, and Mn. The mean concentrations (μg/g dry weight) ranged from 0.1 to 7.8 for Pb, from 1.9 to 8.8 for Ni, from 1.5 to 11.1 for Cd, from 2.5 to 14.1 for Mn, from 47.2 to 64.6 for Zn, from 5.4 to 18.7 for Cu, and from 154 to 558 for Fe. Collecting clams in sites apparently pristine is no guarantee that metals will be in low concentrations.

Gonadic conditioning of the calafia mother-of-pearl oyster, Pinctada mazatlanica (Hanley, 1856), under two temperature regimes.

Abstract Gonadic conditioning of pearl oyster Pinctada mazatlanica was studied under two water temperature regimes using cultured specimens. Before starting conditioning, specimens were induced to spawn with thermal shock. Two different regimes were evaluated, controlled temperatures (CT) and gradually increasing temperatures (IT). In both trials, specimens were fed daily with Isochrysis galbana and Chaetoceros gracilis in a proportion of 7:3. Gonad and muscle samples were excised from the oysters every 15 days and processed for histological analysis. Condition Index and Muscle Condition Index were calculated. Similarly, oocyte frequency and oocyte diameter measurements were made. ANOVA analyses were used to test significant differences in the frequency and diameter of postvitellogenic oocytes, and values of both condition indexes between temperature regimes, and over time. The IT showed more suitable conditions for gonad conditioning than CT, although the time needed for reaching maturity was higher in the former regime. For CT, a temperature of 24°C was the best for conditioning, since there were no traces of atretic oocytes, partially spawned specimens, and there were less previtellogenic oocytes and more postvitellogenic oocytes filling the follicles. At 20°C, no positive results were noticed. Condition indexes appear to be reliable indicators of gonad activity during conditioning in both trials. The ANOVA analysis detected significant differences in almost all the statistical treatments run for oocyte frequency, oocyte diameter and condition indexes according to temperature regime and over time.

LARVAL AND EARLY JUVENILE DEVELOPMENT OF THE VOLCANO KEYHOLE LIMPET, FISSURELLA VOLCANO

Abstract Larval and juvenile development were studied in the volcano keyhole limpet Fissurella volcano over 77 days under laboratory conditions at temperatures ranging from 18°C to 20°C. Larvae obtained by spontaneous spawning were fed a mixture of the microalgae Nannochloropsis oculata and Phaeodactylum tricornutum. Elapsed time from fertilization to veliger larva was 22.5 h. Veliger release occurred on day 3. Formation of the fissure giving rise to the keyhole began after day 16. On days 28 through 33, the keyhole reached its final position and juveniles exhibited adult-like morphological characteristics.

Settlement and Early Nursery of Juvenile Anadara grandis (Pelecypoda: Arcidae) Under Different Conditions at the Hatchery and Ponds

ABSTRACT Fifteen-day pediveliger larvae of Anadara grandis (shell length, 230 ± 20 µm (mean ± SD, n = 20) were cultivated up to the juvenile stage by testing 2 densities: 71 larvae/cm2 and 283 larvae/cm2 for 37 days. During this time, we registered morphological changes of the larvae from pediveliger up to the juvenile stage, as well as absolute growth, and growth and survival rates. The growth rate was 53.5 µm/day at a density of 71 larvae/cm2, with a survival of 60%; at a density of 283 larvae/cm2, the growth rate was 33.6 µm/day, with a survival of 40%. Subsequently, the juveniles obtained were nursed for 57 days in 2 types of experimental units: Nestier trays suspended in a pond and cylindrical upwelling containers with increasing water flow in the laboratory. In each experimental unit we cultured 66,666 juveniles with a shell length of 1.57 ± 0.05 mm (n = 20). In the Nestier trays, growth was 4–6 µm/day, with a survival of 15%. In the upwelling-type units, growth was 5–6 µm/day, with a survival of 93%. ANOVA revealed significant differences (P < 0.05) in juvenile growth between the Nestier trays and the upwelling-type containers. Low juvenile survival in Nestier trays is attributed to clogging with wind-blown slime. However, a nursery of A. grandis juveniles in ponds requires further research to show its economic feasibility.