The histological characteristics of oocyte atresia were examined in the Manila clam Tapes philippinarum (Adams and Reeve, 1850), at Croisic Traict on the French Atlantic coast, over 4- and 5-month gametogenic periods (May to August 2015 and April to September 2016). Atresia was found at all stages of gametogenesis, as well as in residual oocytes, and was characterized by several characteristics: loss of the nucleolus, nuclear degradation, altered cytoplasmic staining affinities, cytoplasmic retraction, and finally the loss of all cellular content. Histological observations indicated that T. philippinarum partially spawned repeatedly over the gametogenic period. Stereological counts showed that at least 15% of the oocyte volume was occupied by atresic oocytes (AO) at the onset of gametogenesis before any spawning activity; this increased to 30% in the middle of the gametogenic period (including both pre- and postspawning oocytes) and 80% at the end of the gametogenic period (postspawning atresia). Of all oocytes whose fate could be determined during active gametogenesis, nearly half were atresic. Similar observations were made for smaller sample sizes of clams from two other sites in nearby Bourgneuf Bay over a 26-mo period. Both AO and nonatresic oocytes were observed in the same gonad acini, suggesting that the process was either not propagated or not synchronized. The considerable proportion of oocytes affected by atresia underscores the need for better recognition, documentation, and integration of this process into models of reproductive effort and fecundity in this species. In particular, condition indices based on tissue : shell weights should be interpreted as estimations of reproductive investment, not as indications of potential reproductive outcome.

Manila clam is widely distributed and cultured along the coasts of China. To assess genetic variation in selected strains cultured in China, four selected strains or populations, zebra (Z), white (W), orange (O), and white zebra (WZ), along with one wild population from Lvshun were analyzed with 10 microsatellite loci. The observed heterozygosity ranged from 0.335–0.538 across populations. The highest expected heterozygosity value was detected in the Z strain (0.716), whereas the lowest value was found in the WZ strain (0.578). F_ST revealed significant differentiation between all pairs of populations. The differentiation between the W strain and the O strain is the lowest (F_ST = 0.086). whereas the differentiation between Z and WZ strains was the highest (F_ST = 0.337). There was no significant reduction in heterozygosity in all four selected strains; however, the number of alleles per locus was considerably lower in the selected strains than in the wild population. These results provide valuable genetic information for the preservation, management, and further selective breeding of the Manila clam.

A novel histological and ultrastructural study of the three ganglia types of Scrobicularia plana was made. Adults of both sexes and immature specimens were collected at Ria Formosa lagoon, Portugal. For light microscopy, animals fixed in formalin were processed for various staining, including serotonin and dopamine immunohistochemistry. For transmission electron microscopy, dissected ganglia were fixed in glutaraldehyde and routinely processed. Every ganglion reveals an outer cortex and inner medulla, with the cortex displaying large and small neurons. Their sizes decrease as they are located closer to the medulla. Almost all are unipolar, and only a few are bipolar. Glial cells appear around the neurons and amidst the axons. They usually have smaller sizes and greater nucleus-cytoplasm ratios. The glial morphologies (fusiform, roundish, and triangular) may correspond to glia subtypes and/or functional statuses. Ultrastructural differences from earlier studies were noted, mainly in the type of inclusions and vacuoles. Serotonergic and dopaminergic cell bodies and neurites exist in all ganglia. There is an identical expression pattern in adults (both sexes) and in immature animals. Nevertheless, the extent/intensity of serotonin positivity in visceral ganglia supports that mature animals have a stronger expression, which may be connected the role of that amine in gonad maturation and spawning.

Razor clams Solen gordonis are commercially harvested during early January to late April in Sasebo Bay, Kyushu, Japan. The fishery has substantial impact on the population because of noncatch mortality being roughly equal to fishing mortality; nevertheless, a municipal project of Sasebo City aiming to improve harvesting and to commercially brand S. gordonis clams harvested from the bay has been in progress since 2012. Despite the increasing commercial demand and fishery impact on the population, information about its reproductive cycle remains unclear. To reveal the reproductive cycle of the population, 25–51 clams with no foot breakage (281 individuals in sum total) were collected from the bay at almost monthly intervals during February to December 2016, and their sexes and reproductive stages were histologically determined. The reproductive cycle of the population showed a period of reproductive resting during February to July, gametogenesis sharply advancing in September, and spawning occurring during October to December, with a peak in November. This cycle was well synchronized between sexes (sex ratio = 1:1). This study is also the first report of gonadal infection by trematode and Marteilia-like parasites in S. gordonis clams. In conclusion, the present study revealed the reproductive cycle of the S. gordonis population in Sasebo Bay and confirmed that spawning season closure for the population has already been achieved by the present harvesting schedule.

The giant clam Tridacna noae is a recently resurrected taxon distinguished from Tridacna maxima on the basis of reproductive isolation, mitochondrial DNA differences, and mantle morphology and ornamentation; however, the morphological characteristics used to distinguish the two species are not consistent with genetic assignment throughout their zone of overlap. This has led to the suggestion that hybridization occurs and constituted a need to reexamine the reproductive isolation of T. noae and T. maxima. This study provides evidence that sympatric populations of T. maxima and T. noae in the center of their range overlap and can hybridize and produce juveniles. Breeding trials using T. maxima and T. noae for both maternal and paternal hybrid crosses were conducted to compare larval and early juvenile development. The fertilization success and survival of both hybrid crosses suggest potential for T. maxima and T. noae hybrids to exist in nature. On this basis, the previously reported reproductive isolation between T. maxima and T. noae may not be apposite across their zone of overlap. Future genetic, population demographic, and ecological studies should consider the possibility of hybridization between T. maxima and T. noae.

The prevalence of parasites in gonads of the clam Megapitaria squalida (Sowerby, 1835) was investigated at Santa Rosalía mining port in the Gulf of California. A total of 696 gonads were histologically analyzed, observing an unusual parasitic castration caused by the development of trematode larvae within follicles. Trematode sporocysts within follicles containing germinal balls and developing cercariae were observed and associated with an inflammatory response, as evidenced by a heavy hemocytic infiltration and the formation of granulocytomas surrounding the parasite structures. Some metacercariae were observed within ovarian connective tissues suggesting that M. squalida could also act as a second intermediate host for digenean trematodes. Infection was age specific as juvenile clams (1-4-cm shell length) did not contain parasites and prevalence in the adult clams increased with size. Unlike males, which presented four levels of infection density, all the parasitized ovaries of females showed very high infection densities. The prevalence was significantly (χ² = 6.99; df = 1; P = 0.001) higher in females (30.2%) than in males (17%). The highest prevalence of parasitized clams was in the ripe stage during the summer (43.7%) when seawater temperatures were highest, whereas the lowest prevalences were observed in winter. It is possible that the polluted environment of Santa Rosalía could increase the occurrence and high infection density by trematode larvae in M. squalida.

Advances in oyster farming have been achieved with biotechnological applications, such as chromosome manipulations aimed at polyploidy. The bivalve Anomalocardia brasiliana is of considerable importance to artisanal fishing activities and is a potential organism for aquaculture in Brazil. The cytogenetic behavior of polar bodies during meiosis provides essential information for chromosome manipulation directed at the production of triploid organisms. The objective of the present study was to identify postfertilization times in which the polar bodies are expelled and determine the most frequent number of chromosomes in A. brasiliana. Individuals were caught on the coast of the state of Pernambuco, in northeast Brazil, and subsequently induced to release the gametes. Samples of the oocyte solution were taken before and every 2 min after fertilization. The material was fixed in Carnoy's solution, stained with 4′,6-diamidino-2-phenylindole and photographed under an epifluorescence microscope. Among the 50 oocytes analyzed in metaphase I, 19 bivalents were found. The release of the first polar body was detected 10 min after fertilization among 70% of the eggs, whereas the second polar body was released at 16 min among 62% of the eggs. This work provides relevant information on the time of initiation of shock treatments for chromosome set manipulation, aiming triploids of this important marine fishery resource in Brazil.

The Gilbert Bay (GB) Marine Protected Area (MPA) on the southeastern coast of Labrador was established in 2005 to protect a resident population of Atlantic cod (Gadus morhua). Commercial dredging for Iceland scallops (Chlamys islandica) in the bay was permitted to continue under MPA regulations, but was excluded from areas of cod spawning. The average size of Iceland scallops harvested in GB is smaller than in the Strait of Belle Isle approximately 150 km to the south. Local fishermen have suggested this is due to slow growth, and this prompted the present study to test the hypothesis that Iceland scallops grow more slowly in GB than in the Strait of Belle Isle. Scallop growth was parameterized as change in shell height with age. Three methods of aging individual scallops were used: interpreting external growth rings on the shell, counting growth increments on the calcareous portion of the shell hinge ligament, and counting internal shell layer growth zones. Counting ligament growth increments and internal shell layer growth zones gave similar estimates of age. In comparison, interpreting external growth rings on the shell underestimated the age of individual scallops. If the ligament method and the internal shell layer method of aging are accurate (scallops of known-age were not examined), scallops in GB require eleven years of growth to recruit to the fishery (attain a shell height of 60 mm). This is substantially longer than the 6-y period estimated using the external growth rings method of aging. Growth rate parameters of Iceland scallops in GB, the Strait of Belle, and in the Nuuk area of West Greenland were found to be similar. The relatively small shell size of scallops presently harvested in GB is not due to anomalous growth, but more likely attributable to repeated dredging of scallop beds in the past and removal of the larger individuals.

After several decades of stock decline, the Atlantic sea scallop (Placopecten magellanicus) resource has rebounded to become one of the most valuable fisheries in the United States. The continued sustainability of this fishery is supported by catch limits determined by annual stock projection models. Incidental mortality is an important term in these projection models, but is historically difficult to measure. Current estimates are derived from field experiments that relied heavily on qualitative observations and as a result are based on limited data with low precision. To better quantify incidental mortality, a multiple before—after-control—impact experimental design was used to measure the effect of scallop dredging on the disposition of sea scallops that remain uncaptured on the seafloor following dredging. An autonomous underwater vehicle was used to collect color photographs and side-scan sonar images of the seafloor before and after controlled dredge treatments in the mid-Atlantic and Georges Bank regions. Approximately 170,000 photographs were annotated for instances of mortality. Dredge-induced incidental mortality of 2.5% and 8% was estimated for the mid-Atlantic Bight and Georges Bank sites, respectively, a difference that is likely attributable to the relatively harder substrate of the scallop habitat on Georges Bank that results in greater physical trauma to the uncaptured scallops. This study provides a quantitative estimate of incidental mortality using a noninvasive platform that offers precise mission navigation for repeated surveys. The spatial scale and distribution of the study sites are broad relative to past incidental mortality studies, and the substrate types at each are common in the sea scallop fishery. Estimated mortality rates are lower than the values currently used in fishery stock models and suggest the existing values are conservative, but likely appropriate estimates for management purposes.

Flatfishes are routine bycatch in the Atlantic sea scallop Placopecten magellanicus (Gmelin) dredge fishery but must be discarded at sea. Despite release, a 90% mortality rate is assumed for overfished species such as yellowtail flounder Limanda ferruginae and windowpane Scophthalmus aquosus.When the scallop fishery exceeds the annual catch limit for yellowtail flounder, accountability measures may be triggered and seasonal closures of the scallop fishery can occur in specific areas. Flatfish bycatch is potentially reduced by stopping the scallop dredge in midwater to allow escape. This technique has been voluntarily practiced, but not widely adopted, owing to a lack of knowledge about its efficacy relative to collateral scallop loss. In a test of 122 scallop dredge tows on a commercial vessel using otherwise standard procedures, pausing the dredge during retrieval significantly reduced flatfish bycatch relative to pause length (0, 5, 10, or 15 min) but also allowed some scallop escapement. Flatfish were more likely to escape from paused dredges if there were fewer scallops in the dredge. Video provided evidence that flatfish do escape through the tickler chains and over the lip during pauses, and also showed the benefit of time in allowing them to work free of the suspended scallop load. During rough weather, vessel heave winnowed the dredge contents, increasing scallop loss. Captains can judge the practice as a cost-benefit calculation to avoid loss of revenue from early closure, but it appears to offer only a weak return on the time investment. Escaped fish may still suffer mortality.

Laboratory-scale research involving marine bivalves maintained in recirculating or closed aquaria requires control of seawater quality parameters. Among them, the total dissolved ammonium nitrogen (TAN), NH₄ ammonia (NH₃) nitrogen, concentration is a critical parameter because of its potential toxicity, mainly in closed systems. This study assessed the efficacy of two macroalgal species collected in Golfo Nuevo (Patagonia, Argentina) in removing TAN from the seawater of experimental systems containing the Tehuelche scallop (Aequipecten tehuelchus). The use of the traditional nitrifying bacterial biofilter was also explored. Scallops were collected from the Gulf of San José (Patagonia, Argentina) where they support an artisanal fishery of great socioeconomic importance. This resource is currently threatened by declining landings observed in the previous years, and experimental research is needed to explore the best conditions for ex situ cultivation. A 14 day-experiment was conducted in 3-L beakers containing an adult scallop with addition of a biofilter (treatment T1: containing Ulva spp.; T2: Undaria pinnatifida; T3: bacterial biofilter; and T4: mechanical filtration before Ulva spp. addition). Negative controls (NC) (no scallop or biofiltration) and positive controls (PC) (without biofiltration) were also performed. The concentration of TAN was measured at the beginning of the experiment and every 48 h, and temporal patterns were described by regression models. Removal efficiency relative to PC was calculated on days 8 (Rd8%) and 14 (Rd14%). Ammonia concentration was estimated as a function of seawater temperature, pH, and salinity. In PC, TAN increased at a rate of 0.03 mg·L^-1·h^-1, reaching a final mean value of 9.85 mg·L^-1 for total dissolved NH₄ -N NH₃-N (TAN-N) (12.69 mg·L^-1 TAN) and 0.15 mg·L^-1 for NH₃. In T1, TAN ranged from 0.02 to 0.22 mg·L^-1 TAN-N during the first 10 days of the experiment (below those measured in PC, T2, and T3), and Rd8 and Rd14 were 98% and 84%, respectively. The highest TAN concentrations observed in the whole experiment were measured in T2, exceeding those in PC. In T3, TAN-N mean concentrations on days 8 and 14 were 1.45 mg·L^-1 (Rd8 73%) and 0.45 (Rd14 95%), respectively. In T4, a linear increase of TAN was observed during the mechanical filtration period; after Ulva spp. addition, TAN decreased to levels as low as those measured in NC (<0.025 mg·L^-1 TAN-N) until the end of the experiment (Rd14 100%). These results show that Tehuelche scallops may be relatively resistant to TAN and that NH₃ concentrations were higher than several safety standards. The seaweed Ulva spp. provided the most efficient biofilter between both tested seaweeds, and its usage would represent a good alternative for the traditional bacterial biofilter in small-scale aquaculture experiments, including long-term acclimation. This information is useful for conducting experimental assays of this overexploited artisanal scallop resource from the Patagonian coast.

The Catarina scallop Argopecten ventricosus is a true functional hermaphrodite, in which male and female gamete cells develop synchronously in one gonad organ spatially divided into a testis and an ovary. Tetraploid Catarina scallops were produced and macroscopic observations showed a significant reduction in the total area allocated to the testis of this functional hermaphrodite when compared with diploids. Further micro and ultrastructure analyses indicated that gamete cells are larger in tetraploids than diploids and that the clear separation between sexual gonadal areas usually observed in diploids was partially lost in tetraploids, with some male acini projecting into the ovary area adjacent to the testis area. The reduced testis area was present in two generations of tetraploids mated between them, indicating its inheritance. A genetic mechanism of sex determination similar to that observed in the nematode Caenorhabditis elegans is proposed to explain the reduced testis area in tetraploid scallops and the rare occurrence of “only males” or “only females” in this and other true hermaphroditic scallops.

This study reports the basic nutritional requirement of subtropical Modiolus capax broodstock conditioned under nine diet—temperature treatments. The value of carbohydrate-rich diets was not only assessed to ensure maturation outside of the main breeding season but also to understand the interaction between diet—temperature over conditioning periods larger than the 30 days usually recommended for tropical bivalves. The experimental design included a natural diet prepared with a blend of the microalgae Tisochrysis lutea and Chaetoceros calcitrans (Micro100) and two carbohydrate-enriched diets composed of Micro100 wheat flour (MicroW) at 7% total dry weight of body tissues and Micro100 cornstarch (MicroC) at 7% total dry weight of body tissues. Maximum gonad development occurred in mussels fed MicroC at higher temperatures (26°C) where the highest frequency of partial spawning accompanied the highest lipid content in gonad and lower carbohydrate content in somatic tissues. This result reflects an early maturation compared with brood stock fed the natural Micro100 diet at 24°C. Lower temperatures (22°C) delayed maturation in all treatments and favored accumulation of carbohydrate reserves in somatic tissues with the MicroC diet. Natural diets supplemented with carbohydrate-rich sources by cereal flours are reliable alternatives to fuel and sustain gametogenesis in M. capax broodstock at high temperatures and to increase carbohydrate reserves in somatic tissues at low temperatures.

To clarify the composition of food ingested by blue mussels (Mytilus edulis) in the Menai Strait, where the largest mussel bed in the United Kingdom lies, hydrodynamic observations with organic carbon and nitrogen biochemical analysis were conducted. This strait is characterized by a narrow channel and wide tidal flats with large tidal mixing that influences the distribution of particulate organic matter (POM), which is food formussels. The maximum velocities of the tidal currents were estimated to be 0.5–1.0 m s^-1 during northeastward flow and 0.6–1.3 m s^-1 during southwestward flow. The residual current was southwestward and the water flux was estimated to be 510 m³ s^-1. Field observations indicate that the inflow of pelagic phytoplankton into the strait mainly occurred in the northern region of the strait. Resuspended benthic primary production, however, also causes higher chlorophyll-a concentration in the central region of the strait near the mussel bed and its contribution to mussel growth was estimated to be 22%–50%. The concentrations of chlorophyll-a and particulate organic carbon indicated that the POM in the strait mainly originated from detritus. Benthic microalgae is, however, an important factor to understand the total primary production in the strait. The consumption of the primary producers was estimated to be approximately 6.3 t C day^-1. In the phytoplankton community, pelagic and thycopelagic (living in both pelagic and benthic environments) species comprised 59.3%–77.2% and 12.8%–40.7% of the cells, respectively. The primary production by resuspended benthic species in the Liverpool Bay region was considerably larger than that in the Menai Strait region. As a conclusion, theMenai Strait is an area with complex hydrodynamic conditions causing horizontal advection and resuspension of both pelagic and benthic phytoplankton, and this complex would cause the most suitable condition for mussel production.

The relationships of the shell morphological traits, including the byssus dimensions, were recorded and analyzed in sample groups of 18- and 30-mo-old cultured winged pearl oysters, Pteria penguin. All relationships among shell dimensional traits with respect to shell height (SH) in the 18- and 30-mo-old oysters were observed to be positive and significant (P < 0.05). Although allometric growth was observed in both groups, the r² values in the relationship between SH and total wet weight (TW) were higher in old oysters than in young ones. These findings indicate that weight in young oysters is heterogeneous. Moreover, the TW—SH ratio showed a clearer tendency to increase relative to exterior dimensions in old oysters. The r² values in the correlation between SH and maximum dorso-ventral length were the highest in both oyster groups; hence, this dimension is a reliable predictor of SH. On the other hand, the relationships between SH and either hinge length or shell thickness were slightly weak in both age groups. Oysters with no byssus were found only in the younger group. It is possible that older oysters are less susceptible to factors that induce byssus shedding. In young oysters, the length and diameter of the byssus was closely related to the weight of the animal rather than the size of the shell. But, as individuals continued gaining weight, no augmentation in the byssus organ diameter was measured, suggesting a threshold for the byssus diameter in heavier oysters. Because it is possible that byssus size may influence the quality of pearls formed in the oyster due to the proximity of the pearl sac to the byssus root, it is important to consider the weight of the oysters selected or cultivated for pearl production, as this may indirectly affect the quality of the finished pearl product.

Shell dimensions of 588 hatchery-produced Pteria penguin (Röding, 1798) were measured and analyzed to describe morphometric changes in shell form of this species over its life cycle. Oysters ranged from 9.4 to 202.2 mm in dorsoventral height (DVH), 0.1–1,526.9 g in weight and spanned 0.5–5 y of age. Significant positive curvilinear relationships were observed between shell width (SW) and DVH (R² = 0.99, P < 0.001), diagonal length (DL) and DVH (R² = 0.99, P < 0.001), shell thickness (ST) and DVH (R² = 0.98, P < 0.001), and wet weight (WW) and DVH (R² = 0.99, P < 0.001). Trends in the morphometric ratios of P. penguin indicated a proportional decrease in SW and DL with increasing DVH, resulting in a shift from a horizontally elongate to a vertically elongate shell form. The ST of P. penguin remained proportionally stable over its life cycle, whereas its WW increased proportionally by more than two orders of magnitude. Based on the results of this study, future research should examine (1) the relationship between the external shell dimensions and internal nacreous area, (2) changes in nacre deposition rate in different shell locations, and (3) the relationship between soft tissue weight, shell weight, nacre thickness, and DVH of P. penguin. The description of the growth form of P. penguin represents an important first step toward determining optimum half-pearl (mabé) culture procedures for P. penguin in Tonga.

Despite nearly a century of exploitation and scientific study, predicting growth and mortality rates of the eastern oyster (Crassostrea virginica) as a means to inform local harvest and management activities remains difficult. Ensuring that models reflect local population responses to varying salinity and temperature combinations requires locally appropriate models. Using long-term (1988 to 2015) monitoring data from Louisiana's public oyster reefs, we develop regionally specific models of temperature- and salinity-driven mortality (sack oysters only) and growth for spat (<25 mm), seed (25–75 mm), and sack (>75 mm) oyster size classes. The results demonstrate that the optimal combination of temperature and salinity where Louisiana oysters experience reduced mortality and fast growth rates is skewed toward lower salinities and higher water temperatures than previous models have suggested. Outside of that optimal range, oysters are commonly exposed to combinations of temperature and salinity that are correlated with high mortality and reduced growth. How these combinations affect growth, and to a lesser degree mortality, appears to be size class dependent. Given current climate predictions for the region and ongoing large-scale restoration activities in coastal Louisiana, the growth and mortality models are a critical step toward ensuring sustainable oyster reefs for long-term harvest and continued delivery of the ecological services in a changing environment.

Several studies have examined early development in oysters, but few have reported the normal (expected) behavior of meiosis and early mitosis or of the organization of the spindle by the centrosomes. To establish this baseline, normal development of fertilized eggs in Crassostrea virginica from meiosis until the four—cell stage using confocal microscopy was documented. To visualize the centrosomes and microtubules, eggs were stained with antibodies for γ- and a-tubulin. In addition to establishing normal development, two additional features of early development were documented. First, centrosome behavior was documented. The centrosome associated with the female pronucleus disappeared after polar body formation. The single centrosome associated with the male pronucleus duplicated by late anaphase of meiosis II to eventually form the spindle for mitosis I, thus the two centrosomes in the first cleavage were derived from the sperm. Second, linkage between the cell and centrosome cycles was established. In the first and second mitosis, centrosome duplication began at early anaphase. At late anaphase, the centrosomes duplicated and were observed as two distinct units at each pole. Asynchrony was also observed at the four—cell stage between the large and small blastomeres, with chromatin and centrosome duplication showing more advanced stages in the large blastomere. This documentation will serve as a baseline for future studies on chromosome loss in polyploid oysters.

Stable isotope composition of the eastern oyster Crassostrea virginica was characterized from three estuaries in the Ten Thousand Islands (Florida). Freshwater in flow from watershed management is affecting this region and has deeply modified the salinity gradient. Stable carbon and nitrogen isotopes were used to trace specific sources of organic matter and the influence of these sources of carbon on the diet of the eastern oyster in the Greater Everglades. Oysters, as well as particulate organic matter (POM) and benthicmicroalgae (BMA) were sampled in three bays at three different stations from upstream to downstream during both wet and dry seasons. Significant salinity differences were observed in all estuaries between summer (wet) and winter (dry) seasons and were linked to freshwater inputs into the bays. Temperature followed a typical seasonal trend. Oysters were enriched in δ¹⁵N compared with POM and BMA, and similarly or slightly enriched in δ¹³C for both seasons. Lighter δ¹³C values in the upper stations in the estuaries suggest input of organic matter from terrestrial sources. Stable isotopes showed that oysters fed more on POM than on BMA. Condition index of oysters varied between stations and seasons in the three estuaries. Because the quality of organic matter consumed by oysters ultimately impacts the health of the oyster, changes in water quality and quantity of freshwater entering estuaries will have implications for future management of the habitat for this ecologically and economically important species.

The protozoan Perkinsus marinus was identified for the first time in the oyster Crassostrea corteziensis from the state of Baja California Sur, Mexico. Intensities of P. marinus infections increased from 0.5–2 to 2–5 (Mackin scale) when water temperature was experimentally increased to 26°C for 15 days. Although disease-induced mortalities have not been reported in natural populations of C. corteziensis, high injected doses of P. marinus caused mortalities among experimental oysters. To evaluate the response of C. corteziensis with increasing levels of P. marinus, expression levels were investigated for genes involved in phagocytosis, cellular proliferation, apoptosis, and inhibitors of serine proteases. Oysters with low infection showed higher gene expression of the serine protease inhibitor gene, as well as of genes involved in phagocytosis (nicotinamide adenine dinucleotide phosphate-oxidase, actin, superoxide dismutase, and glutathione s-transferase), and genes involved in apoptosis and DNA fragmentation (tumor necrosis factor and caspase-8). Results of observed mortalities associated with high intensities of P. marinus infection indicated that C. corteziensis is a susceptible host to this pathogen. Phagocytosis and cell death by apoptosis were higher in less-infected oysters, as an apparent result of the increased expression of apoptosis-related genes.

The rock oyster Striostrea prismatica is one of the most abundant species in the rocky coastal ecosystems of the tropical and subtropical eastern Pacific; however, natural banks are overexploited or depleted, so production by culture is recommended. Adult S. prismatica obtained from natural banks were conditioned for gonad maturation and spawning. Fertilization, embryogenic, and larval development were performed under laboratory conditions, then settlement of pediveliger larvae and nursing of postlarvae were performed using downwelling methods to produce spat. The early life cycle (embryonic, larval, and postlarval development up to 5 mm in length) is described. The larval development was completed in 22 days, with survival >25%. The larval and postlarval growths were exponential reaching spat size (5 mm) after 28 days of settlement. The methods used in this study supported successful larval and postlarval culture of S. prismatica and provide a basis for large-scale propagation of this species.

This work aims to provide oyster farmers a tool to estimate the stock biomass to hold in their nursery. Herein, a steady-state single-compartment mass balance model, which includes the feeding activity of oyster spat, was developed. This model applies to nurseries such as floating upweller systems or land-based tanks and estimates (1) the optimal stock as a function of external food concentration or (2) the food concentration required for a given stock. The model was implemented for the Pacific oyster (Crassostrea gigas Thunberg) and is available online:  http://seaplusplus4.com/oysterspatbud.html. The model was evaluated using published data and further tested by simulating a general rule of thumb regarding the spat-holding capacity for a given nursery. According to a general rule of thumb, 1 hectare of a shallow pond can hold between 1 and 3 tons of spat. The model allows to further specify the rule depending on the spat grade to stock. If the spat is around 0.38 g, the model estimates a holding stock within the range of the rule of thumb; however, if the spat is around 0.04 g, the biomass stock sustained is lower (between 0.7 and 2 tons).

Subtidal shell deposits of the edible bivalve Arca noae in the Strait of Messina (Central Mediterranean) were investigated and compared with an adjacent live population, testifying that dead and live populations were similar but distinct. The age–class structure of the two compared populations, whose lifespans ranged from 5 to 7 y, indicated that in this area unexploited Noah's ark stocks have generally low survival and recruitment. Shell morphometrics and size distributions suggested that the shell deposits were descriptive of the premortality population structure, as expected in a mass mortality episode.

Greenlip abalone (Haliotis laevigata) are commercially farmed in land-based systems in southern Australia and are fed formulated diets that typically do not contain macroalgae. In a 90-day study, the growth and nutrient utilization of juvenile greenlip abalone (1.82 g, 23.23 mm) fed diets containing Ulva sp. protein extract (UPE) were investigated. Animals were fed one of the four formulated test diets containing graded levels of UPE (0%, 5%, 10%, and 20%) or a commercial diet that served as a control for the 0% basal diet. Diets were formulated to contain 37% crude protein, 5% lipid, and 17.5 MJ/kg gross energy. The specific growth rate and shell growth rate (µm/day) of abalone fed the four experimental diets were similar. Dietary inclusions of UPE supported the growth of juvenile greenlip abalone and may be used to reduce dietary inclusions of solvent extracted soybean meal, dehulled lupins, and wheat flour. Currently, UPE is cost prohibitive for commercial use in greenlip abalone diet. As UPE is a by-product of the macroalgae industry, the cost of UPE would likely become more economically viable as macroalgae production increases in the future to include in diets for greenlip abalone. Once economically viable, we recommend a dietary inclusion of up to 20% UPE meal for greenlip abalone.

Elevated mortality, triggered by increased water temperatures (>22°C) and associated factors, is a significant issue for land-based abalone farms in southern Australia. The aim of this study was to test the efficacy of the commercial animal feed product Orego-Stim (OS), containing oregano essential oil in reducing the mortality of 3-y-old greenlip abalone (Haliotis laevigata) exposed to high water temperature (25°C). Inclusion levels of 0.0 (commercial control diet), 0.5%, 1.0%, 2.0%, and 4.0% OS were added into a commercial feed formulation and diets were fed to 3-y-old greenlip abalone (67.98 g, 77.01 mm shell length) at two water temperatures (22°C and 25°C) for 47 days. Survival and immune parameters including phagocytic activity, total hemocyte count (THC), and activities of the enzymes superoxide dismutase (SOD) and catalase (CAT) were measured. Survival was high at 22°C with no significant differences in mortality between treatments. Irrespective of this, exposure to elevated water temperature (25°C) resulted in significantly higher mortalities for all diet treatments (P < 0.05), without any effect of diet. Low ferric reducing antioxidant potential values were observed for all diets. Phagocytic activity remained stable for all temperature and OS treatments (48.82% ± 1.31%). The dietary inclusion of OS and increased water temperature increased the THC compared with the commercial control diet treatment at 22°C. Superoxide dismutase was significantly elevated in greenlip abalone fed the commercial control (0.56 ± 0.08 U mL^-1), and CAT was significantly higher when fed the 4.0% OS diet treatment at 25°C (18.93 ± 2.25 nmol min^-1 mL^-1). Despite failing to increase survival, OS significantly enhanced feed intake at both temperatures at 2.0% and 4.0% compared with the commercial control diet treatment, highlighting its ability as a feeding stimulant (P < 0.05).

Mitochondria are essential organelles that provide energy for most eukaryotes. Even though the basic functions performed by this organelle are widely recognized, considerable variations exist on mitochondria from different species because of specific energetic demands and environmental conditions. The respiratory functions of marine invertebrates are known to be highly specialized because these species face continuous environmental challenges affecting their biological fitness and energetic equilibrium. Among marine invertebrates, Crustacea is an ancient and highly diverse phylum that includes numerous biologically, ecologically, and economically valuable species; some of them evolved specific adaptations in response to habitat preferences, such as energy-regulatory mechanisms or alternative adenosine triphosphate (ATP)-producing pathways, which allow them to survive in low-oxygen environments. This review highlights some relevant characteristics of mitochondria from crustaceans, and describes the current state of knowledge about mitochondrial genes, proteins, and their expression. In addition, this paper discusses the ability of crustacean species to synthesize ATP and to elicit a complex response to the oxidative stress induced by the frequent occurrence of hypoxic and re-oxygenation events. The reported inability of crustacean mitochondria to undergo a permeability transition, as a strategy to avoid cell apoptosis, is also discussed. Finally, the strategies adopted by shrimp to face oxidative stress, and the mitochondrial adaptations that allow hypoxia-tolerant shrimp species to survive in low-oxygen environments are examined.

The gooseneck barnacle Pollicipes pollicipes is a very valuable marine resource on the coasts of Spain and Portugal. To maintain the sustainable exploitation of this species, periodical large-scale population assessments are essential. Because of the heterogeneous distribution of these populations in aggregates, together with the difficulties associated with sampling (i.e., access to rocky reefs, wave exposure, high tides, etc.), there is a lack of studies in this regard. In light of these constraints, the coverage, biomass, and available stock of gooseneck barnacle were first estimated using a novel semiquantitative method along a 215-km long coast at 10 fishing zones and three tidal levels. This study contributed to the first assessment of the distribution variability of gooseneck barnacle in the Cantabria region (N Spain), as the first step toward a long-term monitoring goal. The proposed method is based on a general coverage (GC) estimation, by means of (1) quantitative coverage measurements on quadrats (50 cm × 50 cm) located along vertical transects covering the intertidal bandwidth and corrected by tidal level bandwidths, (2) semiquantitative coverage estimates in larger areas, including 5 m on either side of the quadrats along the transect. Biomass samples were collected at each sampling point by scraping the 50 cm × 50 cm quadrat and fresh weight of the samples was measured. This method arrives at the biomass estimates by means of a power regression model for the coverage-biomass relationship. The population distribution pattern along the coast was also explored separately, by commonly used (1) quantitative coverage estimates in quadrats with no bandwidth correction (sample coverage, SC) and (2) semiquantitative estimates, as in the proposed method (transect coverage, TC), both of which included biomass sampling. Biomass and standing stocks values obtained using GC were lower and consumed less sampling time than those obtained by TC, and particularly SC. The results suggest that the proposed method might be suitable for the assessment of P. pollicipes populations in large coastal areas, as it potentially avoids stock overestimation by detecting the spatial distribution heterogeneity and reduces the sampling time.

Crab aquaculture has gained interest all over the world and is a delicacy in many places. Despite the recent progress made by crab aquaculture, diseases are of great concern in the crab industry. Until recently, the major tool for preventing and treating diseases in crab and other aquatic species was antibiotics; however, the use of antibiotics has its own problems calling for alternatives of which probiotics, prebiotics, and synbiotics have proven to be a suitable alternative. Treating bacterial diseases with antibiotics as prophylactic agents is proven not to be sustainable and ineffective. This is because pathogens are able to develop resistance. The purpose of this review was to look at the use of probiotics, prebiotics, and synbiotics in the crab aquaculture industry. From the available literature, it is evident that these immunostimulants have a major role to play in crab culture. The review shows that probiotics, prebiotics, and synbiotics improve the immune response of crabs. It also improves the microbiota of the gut, which leads to better digestion, absorption, and use of diets. It is evident that much has not been done with respect to the molecular mechanism regulating the effects these natural ingredients have on the immune system of crabs. It will, therefore, be prudent that further studies be carried out on how these ingredients affect growth, survival, and immune systems of crab, especially synbiotics which has not been given attention.

Sexual maturity is an important phase of brachyuran's life cycle as it marks the transition of becoming an adult and the ability to reproduce. This article discussed on the types of sexual maturity found in brachyurans and the implication and application of size at the onset of sexual maturity (SOM) in general. In addition, data on the estimates of SOM of brachyurans were collected on a global scale for the period 1971–2015. The 220 maturity data were representative of 133 brachyuran stocks from 23 families and 55 species. The effect of sampling methods and indicators used for the estimation of SOM were highlighted as well. Variation in the carapace width at which 50% of the population reaches maturity (CW₅₀) was apparent between families, species, sexes, and populations within the same species, in addition to latitudinal and temporal variation. The CW₅₀ was in a positive linear relationship with the maximum size (CW_max) for males (logCW₅₀ = -0.28 1.01logCW_max; R² = 0.85, P < 0.001), females (logCW₅₀ = -0.35 1.08logCW_max; R² = 0.96, P < 0.001), and specifically Portunidae (logCW₅₀ =-0.88 1.32logCW_max; R² = 0.69, P < 0.001). The size at maturity data in this review serve as guidelines for stock assessment and sustainable population management of brachyuran species.

In traditional rural areas in China featuring both agriculture and aquiculture, shellfish waste (SW) was widely used, which created the typical rural cultural landscape (RCL). Nevertheless RCL is increasingly homogenized and traditional building techniques are inefficiently transformed; it has become a bottleneck in the reuse of SW whether the following problems can be solved, namely SW in large quantities but at low prices, secondary pollution, and the contradiction between high investments and low yields. In terms of generation background, material performance, and building process, an analysis was conducted on the generation mechanism of RCL with SW. Then the typical construction of traditional RCL was dissected and a new landscape structure was designed to coordinate appropriate technology and landscape features, which can be used to avoid the damage to coastal RCL caused by new structures of brick-concrete in “demolition and reconstruction” through “structural addition.” Finally, through the design research and based on reconstructing the overall ecological space of agricultural heritage. SW is used as material resources in the system engineering of building sustainable landscape systems in rural areas featuring both agriculture and aquiculture, forming the promotion mechanism of “mariculture zone-factories-sites.”