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Two mass mortality events in 2016 and 2019 affecting the eastern oyster in the Mississippi Sound permitted an investigation of population dynamics during the collapse and recovery from systemic stressors capable of producing local extinction. In this study, metrics were reported as true population metrics with values included in proportion to the size class representation in the population. The approach was critical as trends in Dermo prevalence and weighted prevalence varied substantially between size classes, and this permitted elucidation of recovery trajectories not obvious from the population as a whole. The division of the population into larger and smaller size classes revealed a consistent differential in the time series for Dermo prevalence and weighted prevalence; these metrics did not return to levels observed before the 2016 mortality event in the 2-y interim between the 2016 and 2019 mortality events, and prevalence, in particular, remained low in the smaller size class. The time delay in the return of Dermo infection due to a substantial change in the size frequency of the population toward smaller initially uninfected animals is consistent with the differential in Dermo and young oyster cell doubling times and the required time delay, albeit relatively short, for transmission to occur. Gonadal thickness generally tracked with condition index and followed the expected seasonal cycle; any impact resulting from the 2016 mortality event on these metrics appeared to be inconsequential. The relationship between the adductor muscle diameter and shell height varied little over the time series and was much more stable than between the adductor muscle diameter and shell weight, suggesting a change in the oyster shell shape post-2016. By inference, shell weight is more variable among the three metrics in estimation of the condition index and standardization of other health indices. The ability to establish health metrics for both specific size classes and the population as a whole is essential to understanding the temporal impacts of a severe stressor or mortality event on oyster populations. [ABSTRACT FROM AUTHOR]

Basic information on shell dimensions, calcimass and periostracum mass, biomass, and the relation between the condition and reproduction of Mytilopsis leucophaeata was analyzed for a population in the North Sea Canal, the Netherlands. The mean dry flesh weight of individuals with a mean shell length of 12.5 mm showed a peak at the end of June. The mussel reached the highest mean dry flesh weight in the month before the spatfall started. The gonad index (GI) was high in June, followed by a period of decrease until September and a period of increase until November. The condition index (CI) peaked in June and decreased during the remainder part of the year. The range of CI was highest in May when the gonadal development progressed and was smallest in June when the gonadal development was complete. The CI decreased during the rest of the year. Quantile regressions showed a highly significant relation between CI and shell length. Based on the regression coefficients, the CI was maximal at a shell length of 11.4 mm and minimal at 12.5 mm. Condition index variation was highest within a shell length range of 10–15 mm. [ABSTRACT FROM AUTHOR]

High-intensity infection with the protozoan parasite Perkinsus olseni is lethal to the Manila clam Ruditapes philippinarum, especially to juvenile clams; however, how this parasite impacts its host remains unclear. This study was carried out to investigate the effects of P. olseni on the growth, condition index, burrowing behavior, and filtration activity of the Manila clam to elucidate mechanisms by which the infection causes death of the clams. Juvenile Manila clams (5-9 mm in shell length) were challenged with parasitic zoospores and were then reared in seawater for 52 days. Growth and condition index were frequently, but not always, significantly lower in the challenged group compared with the unchallenged group during the challenge experiment. Fewer individuals from the challenged groups compared with the unchallenged groups exhibited lower burrowing activity, when they were placed on sand in wells of 24-well plates. Furthermore, to compare filtration activity, clams from both groups were maintained in separate suspensions of diatoms. Diatom density remained higher in the challenged clams compared with the unchallenged clams, indicating that challenged clams exhibited lower levels of filtration activity. Decreased burrowing activity may cause higher predation rates and make the clams vulnerable to turbulent water and periodic tidal air exposure, resulting in death of Manila clams under natural conditions. In addition, suppression of filtration activity by infection may cause decrease in food and oxygen intake, leading to mortality induced by nutrient loss and hypoxia. [ABSTRACT FROM AUTHOR]

The reproductive cycle of the large trough shell Mactra murchisoni (Deshayes, 1854) from Pegasus Bay, New Zealand, was examined between March 2013 and February 2014. Histological analysis indicated that M. murchisoni is dioecious (there were no observed hermaphrodites) and gametogenic development is synchronous between the sexes. Gonadal development began in May in both male and females, with the first ripe individuals observed in June and July for male and females, respectively. Spawning began in spring, peaking in late summer with resorption taking place around autumn. No resting samples were observed. Condition indices were calculated each month and were at their highest during the period individuals were ripe. These indices were significantly different ( P < 0.05) between the majority of months and indicate that a high portion of individuals' mass was gonadal tissue during ripe periods. Finally, the results displayed parity between the sex ratio ( P =0.2782), reinforcing that the species are dioecious. [ABSTRACT FROM AUTHOR]

Shell growth, weight-specific growth of the soft tissue, and oxygen consumption were measured in native blue mussels, Mytilus spp., fromdifferent locations inDenmark, covering a salinity range from ∼10 to ∼30. The greatest growth rates were observed in mussels growing at average salinities of 25.7 and 29.5, the lowest rates occurred at the location exhibiting the most fluctuating salinity regime over time, with an average 20.5. Individuals in waters with a salinity of 25.7 also displayed the greatest condition index of all locations (12.1mg/cm3, P < 0.05).Mussels from five of six locations displayed similar oxygen consumption rates ( P ≤ 0.83) when standardized to weight (range, 0.78-0.88 mg O2/g/h. Of the salinities noted in the experiment, 25.7 appears to be the optimal salinity in terms of growth and condition, whereas strongly fluctuating salinity obviously involves reduced growth. At first glance, this study may appear to be just one among numerous attempts to describe the effect of salinity on growth and respiration in Mytilus edulis and its Baltic hybrids. However, themajority of studies focus on field transplants and responses to salinity alterations in the laboratory, whereas only sparse information exists on locally adapted blue mussels in relation to their ambient, native salinity. [ABSTRACT FROM AUTHOR]

The oyster pea crab Zaops ostreum (Say, 1817), is a parasite of the eastern oyster Crassostrea virginica Gmelin (1791). This study examined the frequency of occurrence and impact of pea crabs on adult (50-70 mm shell height [SH]) oysters from natural intertidal reefs in Hewletts Creek, Wilmington, NC and artificially created intertidal reefs from Jones Island, NC. The reefs at Hewletts Creek and Jones Island were also sampled in the fall of 2012 to quantify the presence of pea crabs in two cooccurring bivalve species, the scorched mussel Brachidontes exustus (Linneaus, 1758), and the ribbed mussel Geukensia demissa (Dillwyn, 1817). To evaluate the impact of pea crabs on juvenile oysters (mean SH 11.07 ± 0.16 mm), oysters were deployed in Hewletts Creek at three densities during July 2013 and then retrieved in October 2013. The percent occurrence of pea crabs in adult oysters was low on the natural reefs (1%-3.7%), greater on the created reefs (10%), whereas the percent occurrence in the deployed juvenile oysters ranged from 22.5% to 27.6%. The condition index of oysters from all treatments was significantly reduced ( P < 0.05) in the presence of a pea crab; however, pea crabs did not influence ( P > 0.05) oyster SH-length ratios. Juvenile oyster densities did not influence ( P > 0.05) the incidence of pea crabs, although carapace width of pea crabs increased ( P = 0.05) with decreased densities. On the naturally occurring reefs, pea crabs were found in scorched mussels (2.5% incidence) and ribbed mussels (2.0% incidence), but on the created reefs at Jones Island, pea crabs were only found in ribbed mussels (2.0% incidence). Results of this study highlight the impact of this parasite on the host oyster and the potential of this parasite to infect a significant portion of the younger oyster population, which may influence oyster population dynamics, as indicated by low infestation rates in adult oysters. This study also provided a quantitative foundation for understanding the prevalence of pea crabs in alternative hosts, as the pea crab population may be underestimated if multiple hosts are used. [ABSTRACT FROM AUTHOR]

Atlantic salmon (Salmo salar) farms in the Southwest Bay of Fundy area of New Brunswick were investigated for possible advantages of nutritional enrichment for the blue mussel (Mytilus eclulis) when grown in integrated multitrophic aquaculture(IMTA) systems. Mussels grown in IMTA systems may be exposed to higher concentrations of organic matter at the salmon farms that can enhance growth rates and decrease time to market for the grower. In this experiment, mussels were sock-cultured at 2 distances from 2 separate salmon farms (0 m and 200 m), with 3 growth parameters (shell length, wet meat weight, and condition index) measured monthly and compared with the same growth parameters in mussels grown at a reference site outside the aquaculture influence. After a 12-mo period, mussels grown directly on the cages grew faster than mussels 200 m away on all parameters except shell length at 1 location. Mussels grown at 0 m and 200 m performed significantly better (P < 0.05) in all growth parameters compared with mussels grown at a reference site outside the aquaculture influence. Differences in growth and condition index were most pronounced in the fall and winter, when ambient seston concentrations were low. Results of a second study in which growth rates for individually tagged mussels was monitored for a 6-mo period confirmed that there is a significant growth benefit for mussels in integrated aquaculture with salmon compared with mussels grown 500 m away at a reference site. [ABSTRACT FROM AUTHOR]

The reproductive cycle of the cockle Cerastoderma idule was studied by histological techniques and observation of changes in the condition index during three consecutive years in the Ría de Vigo (Northwest Iberian Peninsula). The onset of gametogenesis took place at the end of the summer (September to October), progressed throughout the winter, and the mature stage was finally reached in spring, The first spawning occurred in April and May and, after gonad restoration, another spawning episode took place in May and June. During the summer (July and August), most of the population showed signs of gonad exhaustion, although a less-intensive spawning event was observed at the end of summer and beginning of autumn. This second episode coincided with a phytoplankton bloom, which acted as a stimulus for spawning. Although a simple measure, the condition index proved to be a good indicator of the gonadal cycle, because it reflected adequately the reserve accumulation during gametogenesis, maximum maturity, and gamete emission. The useful information obtained from this study can be applied in shellfishery management. [ABSTRACT FROM AUTHOR]

In this study, the influence of food availability on the gonadal development of the smooth clam Callista chione was analyzed for the first time. Callista chione adults were maintained for 60 days under controlled conditions with two different diet rations: a scarce diet (3% of dry weight of algae by meat dry weight per day) and a high diet (6%). The condition index, gonadal stage, and oocyte size were measured throughout the experiment. Maturation of gonad was achieved in both groups. Nevertheless, the condition index and oocyte diameter were significantly less in the scarce-diet group. These low values seem to be related to a loss in reserve tissue, not to the release of gametes. Thus, in food-limited conditions, the animals use the energy to mature instead of grow. Comparisons with animals from the field were made during all the study periods, and differences were found. In fact, these individuals were primarily in the postspawning stage, and the oocyte size was considerably smaller, coinciding with low chlorophyll a levels. [ABSTRACT FROM AUTHOR]

The annual reproductive cycle of the Indo-Pacific tellinid clam Heteromacoma irus (Hanley, 1845) was investigated, using histology, for the first time in this study. The sex ratio of H. irus collected from a rocky intertidal area on the northern coast of Jeju Island, Korea, was found to be 1:1, indicating that H. irus is gonochoric. In January, most dams were in the resting phase, although a small number of females showed small oogonia on their follicular epithelium. From February to May, oocyte diameter increased rapidly, and fully mature eggs (44.8-56.8 μm) appeared in May. The first spawning males and females were observed in July, when the water temperature reached 18.0°C, and spawning activity continued until the end of August. During September and December, most clams were sexually in the resting stage. H. in,s is considered to be a summer spawner, and annual gametogenesis was closely associated with the seasonal variation of the surface water temperature. Despite warm water temperatures in Jeju, the resting phase of female and male clams at the study site was prolonged from October to March, suggesting that food availability at this site could be poor and may act as a limiting factor in gametogenesis. [ABSTRACT FROM AUTHOR]

The grooved carpet shell clam Ruditapes decussatus (L. 1758) is one of the most popular and profitable molluscs exploited in rearing plots in the Mediterranean. However, annual catch has been declining steadily since the early 1990s. To understand the seasonality of its nutritional value, thus providing an improved basis for economic valuation of the resource, gross biochemical composition, percent edibility, and condition index were investigated during a year with monthly periodicity in a commercially exploited population of the clam R. decussatus in the Ria Formosa, a temperate mesotidal coastal lagoon located in the south of Portugal. Our results show that total and nonprotein nitrogen covaried during the year, resulting in a protein content that peaked in the warmest months. Although complementary in summer, carbohydrate and lipid contents showed irregular annual trends. The observed seasonality was comparable with that shown by studies elsewhere at similar latitudes, and is underpinned by the reproductive cycle of the species. Our results show the clams to be at their prime nutritional value at the beginning of summer, when protein content peaks. [ABSTRACT FROM AUTHOR]

A survey of surfclam (Spisula solidissima) stocks was conducted in an area from northern New Jersey to southern Virginia during June and July 2004 to evaluate the progress of mortality, apparently related to warming of the Mid-Atlantic Bight. One component of the survey was the measurement of condition index at 146 locations from the Delmarva Peninsula to northern New Jersey. The program followed a pilot study in 2002 that suggested that surfclam mortality off Delmarva was likely caused by warmer temperatures that decreased feeding and subsequently led to starvation. Condition index was highest inshore, with the exception of a few of the most inshore stations, and lowest at the offshore edge of the clam's range. An estimate of meat weight for a standard 120-mm clam, from site-specific length-weight regressions, revealed that the animals near the center of the inshore-offshore distribution had a greater weight per length than those living at the edges of the clam's range, probably a result of the influence of temperature on feeding and growth. Low condition in the extreme inshore locations suggests that warmer temperatures continue to affect surfclam nutrition negatively and indicates the continued susceptibility of clams along the southern and inshore range boundary to warming in the Mid-Atlantic Bight. Low condition offshore may be the result of a delay in gametogenesis or inadequate nutrition resulting from low temperatures reducing feeding rate and food supply. [ABSTRACT FROM AUTHOR]

Natural variation in the physiological variables of the eastern oyster Crassostrea virginica from a tropical climate have until now been poorly documented. This study was conducted to characterize the influence of hydrological variables (salinity, temperature, nitrate, nitrite, ammonium, soluble reactive phosphorus [SRP], and soluble reactive silica [SRSi]) on oyster physiological variables (total hemocyte cells (THC), reactive oxygen intermediates (ROIs), agglutination, lysozyme, and protein concentration). Oysters were collected during 3 different months (April, August, and December) from seven sites in Terminos Lagoon SW-Mexico. The association of physiological variables with oyster condition index (Cl) was also studied. The physiological variability explained by environmental variables was high (30.7%) when compared with the variability explained by the condition index (8.9%). The independent effect of salinity explained 69.7% of the total variability in the physiological variables (F-ratio = 3.4; P = 0.002, Monte Carlo test with 499 permutations). Protein concentration was significantly correlated with spatial salinity variation (r² = 0.89; H = 27.01, P <0.0001). Site effects were salinity-protein discriminated (F-ratio = 3.406; P = 0.002). Temperature was not a significant variable in the oyster physiological variability. The oysters from marine freshwater transition zones were less affected in their Cl and physiological parameters than oysters from permanent high (>28 psu) or low salinity conditions (<10 psu). This study represents the first step toward integrating specific C. virginica physiological information from tropical areas. [ABSTRACT FROM AUTHOR]

Spawner sanctuaries, harvest-free areas planted with high densities of adult clams, are currently being used to restore self-sustaining populations of Mercenaria mercenaria (L.) to Great South Bay, New York. To evaluate and guide this restoration, we monitored the condition and spawning of clams transplanted from two source locations in Long Island Sound since April 2004. Transplanted clams were in relatively high condition and gonad ripeness at time of transplant, spawned the first spring and/or summer after transplant, reconditioned and spawned in subsequent years, but rarely reconditioned to as high of levels as when they were first transplanted. All populations exhibited similar annual patterns of condition and gonad ripeness: both peaked in mid to late spring, dropped steeply through summer with spawning, and they were lowest in fall. In some years condition increased during fall, and the higher the condition attained by the end of fall (mid-December) the greater the peak in condition the following spring. Across years and populations, condition at the end of fall explained ~89% of the variance in spring peak condition. Consistent differences in condition through time among some populations suggested that location within the bay as well as clam size impact condition. Because of interannual and locational variability, long-term monitoring of this long-lived species is essential for determining factors affecting condition and reproduction, and the ultimate restoration of sustainable hard clam populations. [ABSTRACT FROM AUTHOR]

This study examined growth, gametogenic activity, condition index, as well as the relationship of the life cycle to environmental parameters of the Cortez oyster Crassostrea corteziensis, which was cultured for 25 mo in the lagoon of Las Guásimas (Sonora, Mexico). We used oocyte diameter and cytological characteristics of the gonad to determine reproductive stages in females and males. The condition index was used to describe the oyster's physiological health. Temperature, salinity, seston, and chlorophyll a, b, and c were recorded at the study site. The Cortez oyster had isometric shell growth, reaching 103.2 ± 1.82 mm height and 150.3 ± 4.98 g total weight. Data were adjusted to the von Bertalanffy growth equation (L∞ = 132.2 mm and K = 1.08 y-1), and survival was about 70%. This native species exhibited a distinctive gametogenic cycle, with the beginning and end of the cycle controlled by seawater temperature fluctuation (15-33°C), which once started, is continuous over a 9-mo period (March to November). Elevated temperature (>25°C) produced high gametogenic activity, exhibiting primary, growing, and mature oocytes, and partial spawning in April, September, and November. The peak spawning event occurred in August, when seawater reached peak temperatures of 31°C to 33°C, which was followed by a significant reduction of the condition index. During winter, storage of nutrients took place, and this appears to be used in the following season for gametogenesis. In general, the condition index was high throughout the study period. Energy for growth and reproduction came from phytoplankton blooms in summer and high concentration throughout the year of nonchlorophyll particulate organic matter. Observations show that this oyster is a protandrous species. High survival, elevated yields, and a long, continuous gametogenic cycle indicate that C. corteziensis has importance in aquaculture in Gulf of California. [ABSTRACT FROM AUTHOR]

To determine if population density in areas closed to fishing in Narragansett Bay is causing differences in the reproductive potential of the organisms, this study used two approaches to determine the reproductive condition of the animals. The first approach consisted in employing a gravimetric condition index (Cl) to evaluate the general condition of quahogs from nine different sites, 3 sites open conditionally for fishing (conditional areas) and 6 sites closed to fishing. The second approach was a determination of gonadal index (GI) of a subset of the sample sites, by histological observation of gonadal tissue sections. Initial sampling included determination of Cl only, and lasted from March 25 to Sep. 22, 2005. The subset of six of the Sites was sampled the next year (2006), every three weeks from April 15 until Sep. 28 to determine Cl and the gonadal index (GI). Results show that there is a significant difference between the Cl of northern quahogs from conditional areas and quahogs from closed areas (P < 0.001). There is a significant difference in GI between sites at (P < 0.10). The Cl in conditional areas was consistently higher than in closed sites indicating that maturation and reproductive stages are more prevalent in conditional areas than in closed sites. When sites were separated into three categories: conditional fishing sites; coves; and Providence River sites, the GI and Cl of the conditional areas were always higher than the Cl and GI of all the other sites. The coves had intermediate indices, and the Providence River sites always had the lowest indices. The results indicate that the populations of quahogs in the closed sites sampled are not completing the gonadal cycle as expected and that the reproductive capability of the quahogs in conditional areas is higher than those in closed areas. Possible explanations to this condition include lower water quality in the closed areas, low dissolved oxygen concentration especially during the summer, poor bottom conditions and high population density. Although, not one single characteristic of the environment is solely responsible for the reproductive condition of the quahog population, density appears to have significant effect. [ABSTRACT FROM AUTHOR]

To determine if natural populations of the eastern oyster possess resistance to Perkinsus marinus, progeny representing several oyster stocks from the Chesapeake Bay and the Gulf of Mexico were deployed at two sites within the Chesapeake Bay. Mortality, P. marinus infection (prevalence and intensity), shell height, condition index, and energy reserves (glycogen, protein, and lipid) were compared between these stocks. Oyster stocks from the Chesapeake Bay had higher intensifies of Dermo infection than Louisiana stocks, with differences among individual stocks. Throughout the 2-y study, a natural Dermo-resistant stock from Tangier Sound (CTS), was identified. Despite infection intensities approaching those of a susceptible Rappahannock River stock (CRB) and higher than a Gulf of Mexico stock (LOB), CTS consistently had lower mortality for the 2-y grow out, and was comparable to a hatchery disease-resistant strain (XE). At a site (Port Kinsale) where the significant parasite was P. marinus, the LOB stock grew to the largest shell heights and had significantly lower intensifies of infection. However, the performance of the LOB stock was comparatively poorer at the other deployment site (Regent Point) where MSX was present. Shell heights were highest overall in the CRB stock at Regent Point, despite high susceptibility to disease. Condition index varied between stocks, although not necessarily along trends of disease resistance since condition was highest in the CRB and XE stocks. Variations in energy reserves were strongly influenced by season, but not disease, or stock origin. The present study shows that differences between stocks contain an underlying genetic component. Differences seen between deployed stocks in mortality, growth, and condition have strong implications for development of selective criteria for an aquaculture-based industry. [ABSTRACT FROM AUTHOR]

The condition index (CI) is a tool that has been used to estimate the effect that different environmental factors have on oyster meat quality. The CI of oysters in five beds in Sapelo Island and the Doboy Sound (Georgia, United States) were calculated using three different methodologies. Values from each site were used to: (1) compare two sites located in relatively large systems (riven sound) and three sites in a small creek to test for differences due to system size and related nutrient availability; (2) determine the effect of a parasite, the pea crab (Pinnotheres spp.), on oyster CI; and (3) determine the effect of differential position of oysters on a bed, with respect to CI (oysters were collected from areas of the bed that are permanently submerged and areas with the longest dry periods between tidal cycles). With respect to the three analyses mentioned earlier, it was found that oyster CIs for sites in larger systems (river and sound sites) were significantly higher than those in sites with lower flux and width (creek sites) and that the presence of pea crabs as parasites can reduce CI by -50%. In addition, no difference in CI was found between oysters collected from different positions in the oyster bed, indicating that the CI was not altered within a site from effects of exposure. This relatively unusual finding is discussed but suggests the robustness of CI as an intersite analysis tool. Not all differences found in the comparisons were significant for all CIs used, but qualitative results among them were consistent. These variations in significance and the adequacy of each method for analysis are briefly discussed. [ABSTRACT FROM AUTHOR]

Sudden salinity drops in Gulf Coast clam growing areas in Florida have been suggested as a cause of seed (juvenile) clam mortality. Laboratory experiments were used to assess short-term impacts of rapid salinity drops on hatchery-produced juvenile northern quahog (= hard clam), Mercenaria mercenaria, in two separate trials. Mortality and condition index (CI) were measured as response parameters. In Trial I, clams were exposed to a salinity drop of 5 ppt, 15 ppt, or 24 ppt over a span of 24 h, and the duration of this exposure was either 3 or 6 days. In Trial II, clams were either immediately immersed or dry-stored for 24 h prior to immersion, representing common treatment patterns by clam growers. In this trial, clams were exposed to acute salinity drops of either 10 ppt or 20 ppt for up to 7 days. Both trials were conducted at ambient seasonal temperatures. Juvenile hard clams were surprisingly robust and resilient to changes in salinity, experiencing less than 5% mortality after relatively abrupt reductions in salinity of 10 to 15 ppt. Nonetheless, salinity declines of the magnitude occasionally observed at clam culture sites, up to 24 ppt, resulted in significant mortality; 17% (Trial I) and 100% (Trial II). Condition index (CI) was an insensitive response parameter. Dry storage of clams did not appear to have an effect on their ability to withstand changes in salinity; storage decreased final survival by <2.5%. Our results suggest that the salinity declines typically experienced at the Gulf Coast aquaculture sites are not of a magnitude or speed to account for the particular seed clam mortality events that spurred this research. However, long-term effects of salinity changes remain to be tested. In addition, reduced salinity may be indicative of a variety of other stressors, such as increased temperature and turbidity, or decreased phytoplankton concentration, which compound the effects of salinity on clam health and survival. [ABSTRACT FROM AUTHOR]

A study of the Noah's Arks (Arca noae) was conducted in Mali Ston Bay, between November 2001 and November 2002. Noah's Arks were collected monthly for the analysis of the condition index (CI), and every 2 mo for biometric measurements. CI was related to seawater temperature, salinity, and chlorophyl a levels, which were measured every 2 wk. Throughout the study, 39% of the A. noae were >50 mm in size. Based on length frequency distribution, a modified Von Bertalanffy growth equation was constructed: L[subt] = 79.19 [l-e[sup-0.34(t-t[sub0])]. Using the modal sizes estimated from the length frequency distributions, the estimated population growth rates of the shell were greater than the individual growth rates estimated from shell sections. Low values for the CI were recorded in December and January, and also in the period from July to October. The highest condition values were recorded from April until June. [ABSTRACT FROM AUTHOR]

The effect of temperature on reproductive maturity of recently spawned penshell broodstock Atrina ,naura (Sowerby 1835) was studied. Penshells were maintained in an open-flow system and were fed to satiation with a mixture of microalgae. Condition index (tissue wet weightltotal wet weight × 100), the rate of maturation, and oocyte quality were followed histologically until spawning. A scheme of six stages, based on histological preparations, was found best to describe the maturation process in the penshell. Results indicate that penshell maturation must be at low temperatures over two months to obtain high quality oocytes in the hatchery, even though the maturation period can be shortened to half that time at higher temperatures. A reduction of the quality of oocytcs is obtained at higher temperatures. [ABSTRACT FROM AUTHOR]

Changes in shell height, tissue dry weight (TDW), mortality, and biochemical composition of Crassostrea gigas were evaluated at two commercial sites in San Quentin Bay (SQB), Mexico, during the first 9 mo post-settlement. Shell growth rates were 1.5× higher at the mouth (0.36 mm d-1) than the head of SQH (0.23 mm d-1). Tissue dry weight was also 7-to 8-fold higher in oysters from the mouth (2.1-2.16 g TDW oyster-1) than the head of SQB (0.23-0.33 g TDW oyster-1) at the end of the 9-mo experiment. Market size (9 cm) was reached after 9 mo at the mouth and at an estimated age of 13 mo at the head of the bay. Highest mortality occurred within the first month post-settlement (50%-60%) and reached approximately 63% to 87% throughout the whole study period. Proteins (48%-64%) and lipids (2%-9%) were the most abundant biochemical components during early spat development. When oysters reached a size between 48 and 55 mm (shell height) in the fall, glycogen (1%-22%) replaced lipids as the main energy depot. The changeover occurred earlier in oysters at the mouth than in oysters from the head of the bay. It is suggested that between-site differences in growth and biochemical composition in oysters are the result of longer immersion/feeding period experienced by oysters at the mouth of SQB. [ABSTRACT FROM AUTHOR]

The gametogenic cycle of the tuatua Paphies donacina is described from histological sections of clams collected monthly from November 1993 to April 1997. Trends in the dry weight condition index (Cl) and gonad indices suggest an annual breeding cycle with continuous spawning over the summer and an inactive winter phase. There was considerable interannual variation with less than 50% of the population being reproductive during the 1994/5 season. There were significant correlations between seawater temperature, the population gonad index and gonosomatic indices of male and female tuatua. Food resources (chlorophyll a levels) fluctuated within and between seasons with values from 4 to 12 μg L-1. These values showed a positive correlation with seawater temperature, but not with any of the bivalve indices. Throughout the study, the population sex ratio was biased toward females, and often there were individuals of indeterminate sex within the population. Dry weight values for standard 40-mm and 90-mm length tuatua varied seasonally, with the smaller length group showing a higher coefficient of variation, consistent with seasonal patterns of somatic and gonad development. Both male and female tuatua show greater reproductive activity early rather than late in the breeding period and the proportion of reproductive tissue was similar for males and females of various lengths. The Cl was not a good indicator of reproductive potential in male or female tuatua. The reproductive strategy of P. donacina is regarded as exploitive, closely determined by environmental seawater temperature. Somatic growth and gonad development occur simultaneously over the summer, but can extend into the winter if sufficient food resources are available. [ABSTRACT FROM AUTHOR]