Carlos Cáceres-Martínez

Changes in lipid content of oocytes of the penshell Atrina maura as a criterion of gamete development and quality: a study of histochemistry and digital image analysis.

ABSTRACT Tools of histochemistry and digital image analysis were used to quantify changes in the coverage area of lipid droplets (lipid content) of oocytes of the penshell Atrina maura during oogenesis and to determine its relation to changes in water temperature and seston content. These data led to calculating a lipid index as a criterion of gamete development and quality. Gonads were collected monthly for 18 mo and prepared for histochcmical processing with Sudan Black B for identification of lipids. Finished slides were digitized for determining stages of oogenesis and variations in the size of oocytes. Two periods of greatest reproductive activity occurred during the study, with a lower peak from November through January (∼15°C; 26 mg/g) and a major peak from April through June (∼20°C; 25–40 mg/g). Oocyte area significantly varied during the stages of active development (516–2,743 µm2), ripeness (1,073–2,930 µm2), spawning (145–2,939 µm2), and atresia (331–2,001 µm2). Lipid incorporation into oocyte cytoplasm followed a clear seasonal pattern, peaking again in winter and spring. Temporal variations in the lipid index and its relation to oocyte diameter were irregular, but also peaked in winter and spring. Histochemistry and digital image analysis resulted in reliable methods for estimating oocyte development and quality in this species, and can certainly be applied in studies of reproduction of other bivalve, invertebrate, and vertebrate species.

Gametogenesis of Atrina maura (Bivalve: Pinnidae) under artificial conditions

Summary Gametogenesis in the Chinese pen-shell bivalve, Atrina maura (Sowerby, 1835) was provoked under artificial conditions in a running water system maintained under constant environmental conditions in semi-closed tanks. The specimens were fed with a diet commonly used in experimental hatcheries. Gametogenesis was described using stereological techniques (based on the oocyte diameters), classical and semi-thin histology procedures, and electron microscopy. Four reproductive stages were recognized based on oocyte size and cytological characteristics of the gonad: early gametogenesis (4–15 μm), growing (16–30 μm), mature (31–45 μm), and degenerating (46–65 μm). During gametogenesis, the auxiliary cells surrounded the oocyte basal region in the growing stage, afterward disappearing. A process of auto- and heterosynthesis characterize the mature stage, and nuclear deterioration and cytoplasmic membrane disintegration define the degenerating stage. The ultrastructural study of gonads showed that the cytological evolutionary process is comparable to those described for other bivalves. Additionally, the use of semi-thin histology permitted observation of oogonia mitosis. The conditioning system used in this experiment allowed the pen-shells to attain gonadal maturity in 35 days. The application of this procedure will permit hatcheries to obtain viable oocytes for larvae culture.

Annual Reproductive Effort of Pacific Winged Pearl Oyster Pteria sterna and Its Relation with the Timing for Planning Pearl Seeding Operations

ABSTRACT Using a combination of stereological and calorimetric methods, we studied reproductive effort of Pacific winged pearl oyster Pleria sterna during an annual cycle in Bahia de La Paz, B.C.S., Mexico. The relationship between changes in the volumetric fraction of germinal and somatic tissues (gonad, digestive gland, adductor muscle, and mantle tissue) and changes in their energy content was analyzed. These data were also correlated with changes in water temperature and availability of food (seston). Because P. sterna spawns several times a year, reproductive effort was estimated ∼400% in terms of energy increase from early development in October 2006 to the spawning occurring in January to February 2007. During this period, when water temperature was decreasing and seston concentration was increasing, P. sterna followed a conservative strategy for allocating energy from reserves previously stored in somatic tissues. In contrast, when productivity dropped in spring, the species followed an opportunistic strategy for sustaining gametogenesis from food energy. In decreasing order, total energy channeled for reproduction came from the digestive gland (23 KJ g 1), adductor muscle (19 kJ g 1), and mantle tissue (16 KJ g 1). Based on these results, we recommend that commercial pearl culture practices be conducted from mid-autumn (October) through early spring (April), when P. sterna is energetically more resistant to manipulation. An additional recommendation is to avoid grafting during the summer (June through September), when the species is energetically exhausted and highly vulnerable to manipulation.

Effect of cadmium, chromium, lead and metal mixtures on survival and growth of juveniles of the scallop Argopecten ventricosus (Sowerby II, 1842)

The effects of Cd, Cr, Pb and their mixtures on the growth and sensitivity of the scallop Argopecten ventricosus were analyzed in this study. Cadmium showed to be more toxic metal to juveniles (96 hour median lethal concentration (LC50) = 0.396 mg Cd/L), followed by lead (LC50 = 0.830 mg Pb/L) and chromium (LC50 = 3.430 mg Cr/L). Cadmium toxicity was 8 times higher than chromium and 2 times than lead. The most toxic combination was Cd + Cr + Pb. (LC50 = 0.302 mg/L). Based on toxic units analyses (T.U.), a synergistic effect was observed for Cr + Pb and Cd + Cr + Pb. (T.U. = 0.374; T.U. = 0.403), and antagonic effects for Cd + Cr and Cd + Pb (T.U. = 1.26; T.U. = 1.43) respectively. The level of effect (from high to low) on the growth of A. ventricosus juveniles was: Cd > Cd + Cr + Pb > Cr > Pb. The EC50 (metal concentration where a reduction of 50% growing rate is observed) obtained were: Cd = 0.018 mg/L, Cd + Cr + Pb = 0.104 mg/L, Cr = 0.51 mg/L and Pb = 4.21 mg/L. These results suggest that A. ventricosus juveniles are more sensitive to these metals in comparison to other juveniles from other bivalve species (e.g., A. irradians, Mytillus edulis, Crassostrea virginica).

Ciclo gametogénico e índice de condición de la almeja Chione fluctifraga en Bahía San Jorge, Golfo de California, México

Abstract.- The gametogenic cycle of the black clam Chione fluctifraga of northwestern Mexico, collected from March 2009through February 2010, was studied using conventional histological techniques and oocyte modal analysis. A conditionindex was also determined. Clams exhibited a semi-annual gametogenic cycle. The species generated the first oocytecohort in spring (April) started its vitellogenic growth and remained continuous over 9 months until early winter (December).A resting period occurs in winter. Clams released gametes continuously throughout the reproductive period, but the mainspawning occurred during the warmest period (>28°C). Gametogenic activity seemed to be strongly regulated by watertemperature. The average growth rate of oocyte cohorts was calculated (0.41 ± 0.10 μm day –1 ), with the most rapid growth(0.67 μm day –1 ) from September through October. The condition index was higher in summer, but other peaks occurred inwinter, producing accumulation of nutrients from increased phytoplankton biomass. The female:male ratio was 1:1.3; nohermaphrodites were detected. A reproductive classification is proposed. These results can help regulate exploitationand establish off-limit periods for this clam in the Gulf of California.

Analysis of different methods to estimate fecundity in bivalve molluscs

Abstract We analyzed the advantages and disadvantages of three methods to estimate potential fecundity in the bivalve molluscs Pinctada mazatlanica and Atrina maura, both species having commercial value in northwestern Mexico. Data of gonad samples collected during the breeding season in March 1999 (P. mazatlanica) and March 2003 (A. maura) were processed with histological techniques combined with Cavalieri’s Principle; stereological analysis of the gonad with the caliper method; and estimation of the theoretical radius of oocytes. These estimates were compared to a reference value obtained from direct counts of the number of oocytes stripped from the gonad. Compared to other methods, potential fecundity determined with the caliper method was more accurate in both species: A. maura (9.8–15 × 106 cells ind−1 and P. mazatlanica (10.8–17 × 106 cells ind−1). The potential of the caliper method, combined with image analysis software may offer accurate estimates of aspects of reproduction in different bivalve species, which has direct applications in hatcheries and conservation programs.

Chapter 29 - Scallop Fisheries and Aquaculture in Mexico

This chapter describes the three most important Mexican scallop species (lions paw: Nodipecten subnodosus; Pacific calico scallop: Argopecten ventricosus; Vogdes scallop: Euvola vogdesi), their ecology, fisheries and aquaculture. All commercially important scallops in Mexico occur in the Pacific Northwest and Gulf of California, especially in the lagoon systems along the coast in shallow waters to depths of about 100 m. The three scallop species are fast growing, reproduce early in life, and form large banks that have been commercially exploited over the past decades by hooka-diving from small fibreglass skiffs with outboard engines. As happened in many scallop fisheries around the world, exploitation is characterised by boom and bust phases. Commercial fisheries of Mexican bay scallop started in the early 1980s and represented the most important mollusc fishery in the country from 1985 to 2013, when the banks in Magdalena bay were diminished so much, that the fishery was closed. Vogdes scallop was only locally exploited for a short time, the lions paw, however, has sustained a small commercial fishery in Ojo de liebre and Guerrero Negro lagoons from the early 1990s to 2010 with a maximum production of about 150 mt of meats. In 2010, the population crashed, probably due to a disease, the cause of which is still being investigated. This species was also fished at different sites in the Gulf of California (Loreto, Bahia de Kino), but on a much smaller scale. Today, all scallop fisheries in Mexico are in a serious crisis and are deemed unsustainable. Therefore, large efforts have been undertaken to develop commercial aquaculture of A. ventricosus and N. subnodosus. While hatchery techniques for the former are fully developed and commercial spat production has been accomplished routinely, hatchery production of the latter is still on a small scale, and no commercial spat supply is as yet available, despite a large number of scientific studies on the subject. Small-scale pilot and commercial cultures of both species have been conducted at >15 sites on the Baja California Peninsula and the coasts of Sonora and Sinaloa over the past two decades, with varying results. No active scallop cultures are in operation as of 2015, which shows that they have not been commercially viable for the most part. Lack of spat production, site selection, El Nino years, diseases, handling, market failures, competition with the capture fishery and mismanagement have been quoted as possible reasons, and the Mexican government does not have a comprehensive programme to promote scallop aquaculture. Unfortunately, the large body of scientific studies on scallop aquaculture in Mexico has not translated into an economic alternative for the aquaculture and fishing industry in the region. As fisheries in the region are clearly in decline, efforts should be strengthened to promote sustainable aquaculture of native species and thereby improve the livelihood of coastal communities.