Mantle regeneration in the pearl oysters Pinctada fucata and Pinctada margaritifera

Mantle tissue in pearl oysters (Pteriidae) is responsible for secreting the mother-of-pearl or nacre lining the shell. When grafted into another oyster, excised mantle tissue, commonly called ‘saibo’, is responsible for cultured pearl production. This study was undertaken to assess the process of mantle regeneration in the Akoya pearl oyster Pinctada fucata and the blacklip pearl oyster Pinctada margaritifera following mantle excision. Prior to saibo excision, oysters were anaesthetized with 2 mL L^−1 propylene phenoxetol. Saibo tissue was excised from 50 P. fucata and 10 P. margaritifera. After excision, all oysters were returned to culture conditions. All oysters were maintained in panel (pocket) nets on a long-line at Magnetic Island, north Queensland, Australia. Oysters were anaesthetized and sacrificed 3, 6, 9, 12, 15, 20, 30, 45, 60 and 90 days after saibo excision to assess mantle regeneration using histological and histochemical techniques. Survival over the 90-day study was 100% and 70% for P. fucata and P. margaritifera, respectively. After excision, the mantle tissue healed within the first three days and began growing as connective tissue. Muscular development was seen between days 60 and 90 after excision. Shell formation abilities were recovered by day 15 when secretory cells and conchiolin secretions were first observed. Both P. fucata and P. margaritifera regenerated mantle to its original extent within the 90-day study. This is the first description of in vivo mantle regeneration in pearl oysters and the results have major implications for the lucrative cultured pearl industry. Our results indicate that mantle tissue donors need not be killed for pearl production. Those producing saibo that results in good quality pearls could be used as future parent-stock in breeding programs or for subsequent saibo donation and pearl production

Effects of cryoprotectant agents and freezing protocol on motility of black-lip pearl oyster (Pinctada margaritifera L.) spermatozoa

Gamete cryopreservation techniques have been applied to several bivalve mollusc species. However, research activity in this area has primarily focused on cryopreserving gametes from edible oysters (Ostreiidae). Few studies have examined the effect of cryoprotectants and freezing protocols in the preservation of spermatozoa from cultured pearl oysters (Pteriidae). Pearl oyster producers are increasingly looking towards the development of improved family lines and, as a consequence, the ability to cryopreserve gametes would bring about significant benefits to the cultured pearl industry. In response to this need, we evaluated the effect of three cryoprotectant additives (CPA) on motility of spermatozoa from the black-lip pearl oyster, Pinctada margaritifera. These additives have previously been used to cryopreserve gametes of other bivalve species. The following CPA mixtures were evaluated: (1) 0.45 M trehalose and 0, 0.64, 1.02 and 1.53 M dimethyl sulfoxide (Me2SO); (2) 0.2 M glucose and 2 M Me2SO and (3) 1.31 M propylene glycol (PG). The effects of four different freezing protocols on motility of P. margaritifera spermatozoa were also evaluated (slow, medium, medium-rapid and rapid cooling).\ud \ud This study showed that total motility was best retained when spermatozoa were cryopreserved in 0.45 M trehalose and 0, 0.64, 1.02 or 1.53 M Me2SO and frozen using slow to medium-rapid cooling rates (2.1–5.2 °C min−1). Rapid freezing through direct plunging of spermatozoa into liquid nitrogen resulted in the lowest overall retention of motility regardless of the CPA additive; however, CPA mixture also influenced retention of motility, with 0.2 M glucose in 2 M Me2SO and 1.31 M PG retaining the lowest levels of motility for the CPAs evaluated

Use of relaxants to obtain saibo tissue from the blacklip pearl oyster (Pinctada margaritifera) and the Akoya pearl oyster (Pinctada fucata)

Cultured pearl production requires mantle tissue (‘saibo’) from donor oysters to be grafted into a number of recipient oysters. Use of anaesthetics is essential to keep donor pearl oysters alive for further utilisation and to minimise damage to them while excising saibo tissue. Propylene phenoxetol and benzocaine were chosen as relaxants as they have proven effective with pearl oysters over a short period of time and allow rapid recovery without mortality. Pinctada margaritifera and Pinctada fucata were exposed to propylene phenoxetol at a concentration of 2.5 mL L^−1 and benzocaine at concentrations of 250, 500 and 1200 mg L^−1. Once relaxed, oysters were observed every 5 min to evaluate the condition of the tissues. Oysters were classified as either ‘suitable saibo donor’ or ‘non-suitable saibo donor’ depending on their suitability for use as saibo donors for pearl production. Survival of oysters in all treatments was 100%. With the exception of oysters exposed to 250 mg L^−1 of benzocaine, where no relaxation was recorded, oysters in all other treatments became relaxed and showed good condition and acceptable characteristics to be used as saibo donors

Variaciones estacionales en el desempeño reproductivo y larvario de la concha nácar Pteria sterna asociadas con condiciones ambientales anómalas

Se estudió el desempeño reproductivo y larvario de Pteria sterna en relación a factores ambientales anómalos, hipotetizando que la transición entre los eventos de La Niña y El Niño 2008-2009 afectó los periodos “normales” para recolectar reproductores maduros y cultivar larvas en laboratorio. Se realizaron muestreos estacionales en 2 periodos reproductivos (febrero y abril 2009), 1 periodo pre-reproductivo (noviembre 2008) y 1 periodo post-reproductivo (junio 2009). De las 40 ostras recolectadas en cada periodo, 20 se utilizaron para evaluar el desove y cultivo larvario y 20 para determinar indicadores de condición reproductiva. La temperatura, salinidad y contenido de seston se monitorearon en cada periodo. Los datos de temperatura superficial del mar (TSM) asociados a condiciones ambientales anómalas se obtuvieron del satélite Aqua-MODIS. Las variaciones en la TSM afectaron más el desempeño reproductivo que el desempeño larvario de Pteria sterna. La inducción al desove falló en noviembre 2008 y fue exitosa en febrero, abril y junio 2009, aunque solo en abril las larvas completaron la metamorfosis y se fijaron, a partir de reproductores más maduros, ovocitos más grandes y condiciones ambientales favorables (21.80 °C; ~31 mg·L–1 seston total; +0.50 °C TSM). Las anomalías positivas de TSM (+0.50 a +1.10 °C) de agosto a diciembre 2008 favorecieron un verano más largo que afectó el desove de febrero 2009. En junio 2009 (22.50 °C, 29.5 mg·L–1 seston total, +0.40 °C TSM), cuando los porcentajes de gónadas y ovocitos maduros eran bajos, las larvas no fueron viables y pocas semillas se fijaron. Además de recolectar reproductores maduros en invierno-primavera para una viabilidad óptima de las larvas y semillas, recomendamos incluir un breve periodo de acondicionamiento en el laboratorio después del pico de desove y un segundo a finales del otoño para promover el reciclaje de nutrientes y la recuperación natural de gametos

Larval abundance and spat collection of the lion’s paw scallop Nodipecten subnodosus in Ojo de Liebre Lagoon, Baja California Sur, Mexico

Large numbers of spat of giant lion’s paw scallop Nodipecten subnodosus are required for the development of the scallop aquaculture industry. Despite the large adult populations of this species in Ojo de Liebre Lagoon, Baja California Sur, Mexico, attempts to collect spat with onion bag collectors during the reproductive season (September–November) have not been successful. We assessed lion’s paw spatfall at three sites (La Ventana, El Conchalito, and El Borbollón) within the lagoon, where high recruitment was previously recorded. Netlon collectors instead of onion bags were used and they were deployed at each site at a depth of 1 m on two occasions (October and November 2007) when pediveliger larvae were more abundant. Collectors were retrieved and evaluated in February 2008, after being submerged for 118 or 82 days. Pediveliger larvae were present from late September to late November at all three sites. Densities peaked at 1 m in mid-November and were significantly higher at La Ventana, accounting for 12,400 larvae m–3. Collectors installed in October at El Conchalito showed higher (P < 0.05) mean recruitment (1.7 ± 0.2 spat per collector) than collectors set in November (0.4 ± 0.3 spat per collector). Collectors installed in October and November at La Ventana had 0.6 ± 0.3 and 0.9 ± 0.2 spat per collector, respectively. No significant differences were observed in the growth rates of the juveniles collected. High densities of larvae in the plankton during November indicated that high reproductive activity occurred earlier that month or in late October. La Ventana showed the highest potential for spat collection based on larval abundance, followed by El Borbollón and El Conchalito; however, El Conchalito showed the highest spat recruitment, followed by La Ventana and El Borbollón. Since spat collection was relatively low at all sites, more efforts to determine better collection sites and techniques, as well as appropriate deployment times are required.

Artisanal fisheries in La Paz Bay and adjacent oceanic area (Gulf of California, Mexico)

We analyzed the artisanal fishery capture data for La Paz Bay (Baja California Sur, Mexico) from 1998 to 2005. Capture data were related to the reproductive cycle of each species. Complete fishing records for 18 species of commercial importance belonging to eight families were identified. The most frequently captured species in La Paz Bay was the Pacific red snapper Lutjanus peru, with 43% of the total capture. This species was followed in importance by the spotted rose snapper Lutjanus guttatus, other groupers (Serranidae), and the jacks (Carangidae), with 18.8%, 15%, and 7.3% of the capture, respectively. Other commercial species captured in smaller amounts included the yellowfin tuna Thunnus albacares, the California flounder (or California halibut) Paralichthys californicus, the flathead mullet Mugil cephalus, the goliath grouper Epinephelus itajara, and different species of mojarra (Gerreidae). With few exceptions, catches outside the bay were higher than in the inner bay. All species were caught throughout the year regardless of their reproductive season. We recommend the implementation of fishery regulations for La Paz Bay, especially in the case of the Pacific red snapper, since it is the most exploited. Currently, overexploitation and possible local shortage of species may occur at any time and without warning in the near future. Aside from fishery management, an attractive option for increasing the supply of marine resources in the area is to use the inner bay for marine fish farming.

Comparative analysis of the reproductive strategy of lion's paw scallop Nodipecten subnodosus in Baja California Sur, Mexico

The reproductive strategy of lion's paw scallop Nodipecten subnodosus was evaluated in a culturing system in Bahía Tortugas, Baja California Sur, Mexico during an annual cycle, comparing its response with data previously reported at other localities. High frequencies of ripe gonads throughout the year indicate that reproduction was continuous, with two main ripening/spawning events: July-September and December-March. A continuous breeding is also reported for the species in Bahía Magdalena, Bahía Juncalito, and Bahía de Los Angeles. These eutrophic areas are Biological Active Centers where gametogenesis appears to be regulated by the energy taken from recently ingested food following an opportunistic strategy. However, the digestive gland index decreased and the muscle indices increased during one of the breeding peaks, suggesting that some stored reserves are also used to sustain gametogenesis (conservative strategy) partially. High incidences of atretic oocytes are likely associated with atypical daily variations in water temperature from May through September (12 to 33°C), or with stressful conditions in the culturing system in summer. Despite this, the culturing system set in Bahía Tortugas appears beneficial for a continuous reproduction of N. subnodosus