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MONSOONALLY DRIVEN REPRODUCTION IN THE TROPICAL BLACK-LIP ROCK OYSTER SACCOSTREA ECHINATA (QUOY & GAIMARD, 1835) IN NORTHERN AUSTRALIA.

INTRODUCTION

Reproduction in oysters is a cyclical physiological process, which can be continuous, semiannual, or annual; it involves several reproductive stages, including growth and ripening of gametes, spawning, resting, and gonad redevelopment (Bayne 1976, Gosling 2003, Lucas 2012). Variation in the timing and duration of each stage occurs both between and within species. For example, Crassostrea virginica in five tropical lagoons in the Gulf of Mexico showed significant differences in the duration and intensity of their reproductive stages, resulting in a reproductive pattern that varied from annual to continuous, between populations (Aranda et al. 2014). An understanding of seasonal gonad changes in an oyster species, the timing and intensity of spawning, and recruitment, is essential for the management of oyster stocks and for efficiency in aquaculture operations.

Reproductive patterns are regulated by both endogenous factors such as neuroendocrine cycles and genotype and exogenous factors such as water temperature, food, salinity, and light (Gosling 2003, Lucas 2012). Orton (1920) proposed that change in seawater temperature is the most important exogenous factor regulating reproduction in marine bivalves and that each species has a threshold water temperature, which must be attained before gametogenesis is initiated. This has been verified for many temperate oyster species such as Crassostrea gigas (Chavez-Villalba et al. 2003, Fabioux et al. 2005), Saccostrea glomerata (Dinamani 1974, Dove & O'Connor 2012), and Crassostrea virginica (O'Beirn et al. 1996). In the tropics, where water temperature is relatively stable, however, different exogenous factors such as food availability and salinity may have roles in regulating reproduction (Stephen 1980, Christo & Absher 2006, Paixao et al. 2013) and spawning induction (Stephen & Shetty 1981, Southgate & Lee 1998).

Bayne (1976) described a typical tropical bivalve reproductive cycle as extended and semicontinuous. This is true for the widespread tropical oyster Saccostrea cucullata that reproduces continuously at low levels with site-specific peaks, often associated with the monsoon season (Braley 1982). Other species that display a semicontinuous spawning pattern include Crassostrea rhizophorae in Venezuela (Angell 1986), Saccostrea echinata in the Philippines (Lopez & Gomez 1982), Crassostrea madrasensis in India (Nair & Nair 1987), Crassostrea iredalei in Malaysia (Teh et al. 2012), and Crassostrea brasiliana in Brazil (Christo & Absher 2006). Despite being less common, some tropical oyster species do possess restricted spawning patterns with periods of gonad inactivity; these include Crassostrea lugubris in the Philippines (Lopez & Gomez 1982), Crassostrea belcheri in Thailand (Tanyaros & Tarangkoon 2016), and Crassostrea gasar in Brazil (Paixao et al. 2013).

The black-lip rock oyster Saccostrea echinata (Quoy & Gaimard, 1835) occurs throughout the tropics, including the Moluccas, Papua New Guinea, Indonesia, Thailand, the Philippines, northern Australia, and Micronesia (Thomson 1953, Lindsay 1994). This species has considerable aquaculture potential (Coeroli et al. 1984, Glude 1984) and current interests in developing the industry are high (Fleming 2015, Nowland et al. 2018). Few studies have investigated the reproductive biology of S. echinata and, of these, dissimilar findings have been reported. Lopez and Gomez (1982) reported low numbers of ripe oysters occurring in all months, except September, and suggested that S. echinata continuously spawns in the Philippines. Braley (1984) reported one complete (May) and a partial (November) spawning peak for S. echinata in Guam, whereas in eastern Australia, Lindsay (1994) reported a single annual spawning peak during summer (December-February) that strongly correlated with water temperature. These inconsistent findings are a major impediment to development of S. echinata as a commercial culture species, based on either wild spat collection (Glude 1984) or hatchery production (Southgate & Lee 1998, Nowland et al. 2018). To address this bottleneck, the aim of this study was to determine seasonal fluctuations in the reproductive cycle of 5. echinata at three locations in the Northern Territory, Australia, and to investigate the influence of selected exogenous factors on seasonal gonad development.

MATERIALS AND METHODS

Study Areas and Biometric Data Collection

Adult Saccostrea echinata were obtained at low tide from intertidal wild stocks at Melville Island (MLV) (11[degrees] 15' 07" S, 130[degrees] 20' 53" E), Goulburn Island (GLB) (11[degrees] 38' 49" S, 133[degrees] 25' 23" E), and Mooroongga Island (MRN) (11[degrees] 56' 06" S, 135[degrees] 02' 47" E) (Fig. 1). Oysters were collected every 4-6 wk (n = 13-23) from January 2016 until June 2017, except for site MLV, where collection ceased in September 2016. Oysters ranged in size from 56.3 to 192.2 mm [dorsoventral measurement (DVM)] and 32.0 to 140.7 mm [anteroposterior measurement (APM)]. Oysters were transported live and without water in a damp hessian bag, inside a foam box to the Northern Territory Government Department of Primary Industry and Resources, Darwin Aquaculture Center and processed within 24 h of collection. Fouling organisms and sediments on oyster shells were removed, each oyster was given a unique identification code, and photos of each oyster were taken on waterproof grid paper (5 mm grids) for later measurement of DVM and APM using the program Grab It (DataTrend Software 2018). Whole oyster weight was determined using an electronic balance with precision of 0.1 g, before the visceral mass was extracted from the shells and excess water removed by placing onto tissue paper for 2 sec on each side. The visceral mass wet weight was determined using an electronic balance with precision of 0.001 g and shell weight was determined using the same electronic balance as used to determine whole oyster weight. The wet weight condition index (CI) was determined for each oyster and calculated following Hopkins (1949):

CI =[v/w-s] x 100. Eq. 1

where v is the visceral mass wet weight (g), w is the whole oyster weight (g), and s is the shell weight (g).

Histology

Transverse 6-mm-thick cross sections of the dorsal visceral mass, from the point where the labial palps meet the gills, and parallel with the hinge line, were made for each oyster. The sections were then placed into histological cassettes, fixed in 10% seawater formalin for 48 h and then processed and embedded in paraffin. Sections of 4 [micro]m were made using standard histological techniques (Luna 1968, Raphael et al. 1976) and stained with hematoxylin and eosin for histological evaluation.

Sections were assessed microscopically to determine gender and reproductive condition according to the Dinamani (1974) classification system described for Saccostrea glomerata; where allocation of various phases of gamete development were determined primarily on nuclear features, cell size, and staining characteristics, for example, resting (R), early development (G1-G2), late development (G3), ripe (G4), discharged (G5), and residual (Gx). When more than two stages coexisted in the same sample, the dominant stage was assigned to the specimen.

Mean Gonad Index

Mean monthly gonad index (GI) was determined for each sampling site and was calculated following the formula described by Seed (1969):

M = [[SIGMA](ns)/N], Eq. 2

where n is the number of oysters present in a given gametogenic stage, s is the numerical ranking of the given gametogenic stage, and N is the total number of individuals in the sample (Seed 1969, Braley 1982, Braley 1984). The following is the numerical ranking (s) scheme for the Dinamani (1974) gametogenic classification system; R = 0, G1 = 1, G2 = 2, G3 = 3, G4 = 4, G5 = 0. and Gx = 0. The index may vary from zero, when all the individuals in the sample have spawned (G5) or are in the resting (R) phase, to four, when all the individuals within the sample are sexually ripe (G4).

Environmental Parameters

Seawater and air temperature were monitored at each site at hourly intervals using two intertidally deployed DST CT data loggers (Star-Oddi, Iceland), and data were downloaded using the SeaStar application software (Star-Oddi). Rainfall data were obtained from the Australian Government Bureau of Meteorology daily monitoring stations at Pirlangimpi Airport (18.57 km from the MLV site), Warruwi Airport (4.55 km from the GLB site), and Milingimbi Airport (10.34 km from the MRN site) (BOM 2018).

Statistical Analysis

Biometric data (whole weight, visceral mass wet weight, DVM, APM, and CI) and air and water temperature data were tested for homogeneity of variance. Whole weight and visceral mass wet weight data were log-transformed. All data were then analyzed with a one-way ANOVA followed by post-hoc Tukey HSD test to determine differences between sites and seasons (monsoon season = November-April and dry season = May-October).

Transformation of rainfall data across all sites could not correct for heterogeneity of variance. Therefore, a Bray-Curtis similarity resemblance matrix was created, replacing the large number of zeros with a one. Then the PERMANOVA function in PRIMER-E version 7 (Clarke & Gorley 2015) was used to test rainfall differences between sites and seasons in a one-way fixed-factor design. The Pearson correlation coefficient was used to determine the presence of linear relationships between CI or GI and environmental factors (temperature and rainfall). Pearson chi-square tests were used to compare gender ratios between sampling sites and seasons. An ANOVA was also used to determine differences between oyster size (DVM and APM) and gender. Analyses were completed and plots generated using R (R Core Team 2017).

RESULTS

Biometric Data

A total of 527 (MLV = 98, GLB = 228, and MRN = 201) oysters were sampled. The mean whole weight of oysters from MLV was 269.6 [+ or -] 15.0 g, with 15.78 [+ or -] 0.67 g visceral mass wet weight, and mean DVM of 105.3 [+ or -] 2.1 mm and APM of 79.3 [+ or -] 1.3 mm. The mean whole weight of oysters from GLB was 289.5 [+ or -] 9.9 g, with 14.64 [+ or -] 0.47 g visceral mass wet weight, and mean DVM of 103.1 [+ or -] 1.4 mm and APM of 84.4 [+ or -] 1.1 mm, whereas the mean whole weight of oysters from MRN was 351.1 [+ or -] 16.5 g, with 11.66 [+ or -] 0.37 g visceral mass wet weight, and mean DVM of 111.8 [+ or -] 1.6 mm and APM of 78.7 [+ or -] 1.4 mm. Whole oyster weight and visceral mass wet weights were significantly different across sites (F = 7.87; df 2/481; P < 0.001 and F= 17.97; df 2/493; P < 0.001, respectively), and post hoc Tukey HSD tests showed that oysters from MRN had significantly (P < 0.001) larger whole weights and significantly (P < 0.001) smaller visceral mass wet weights than oysters collected from MLV and GLB. The DVM and APM of oysters were also significantly different across sites (F = 8.61; df 2/481; P < 0.001 and F = 7.60; df 2/479; P < 0.001, respectively). Post hoc Tukey HSD tests showed that oysters from MRN had a significantly larger mean DVM than those collected from MLV (P < 0.05) and GLB (P < 0.001), whereas the mean APM of oysters collected from GLB was significantly larger than that of oysters collected from MLV (P < 0.05) and MRN (P < 0.001). No sexual dimorphism was observed macroscopically.

Condition index of oysters varied across all sites (Fig. 2) and peaked at 81.7 [+ or -] 3.2 in April 2016 at MLV, 85.1 [+ or -] 2.2 in January 2016 at GLB, and at 85.1 [+ or -] 2.4 in December 2016 at MRN. In the 2016 to 2017 monsoon season (November-April), oysters from GLB registered their lowest CI of 64.6 [+ or -] 2.3 in January 2017, 3 mo earlier than those at MRN (61.2 [+ or -] 4.0). Across all sites, CI had no linear relationship with temperature (r = 0.099; df = 25; P > 0.05) or rainfall (r = -0.245; df = 30; P > 0.05).

Histology and Gonad Index

Histological sections showing female and male gonad developmental stages are shown in Figures 3 and 4, respectively. Even though specimen collection only occurred five times at the MLV site and does not span an entire year, the reproductive patterns were similar in oysters from all three study sites, shown for MLV, GLB, and MRN in Figures 5A, 6A. and 7A, respectively. In general, across all sites, the spawning period occurred from October through April, with residual (Gx) or resting (R) gonad phases predominant from May through September. Specimen collection began in January 2016, toward the end of the breeding season of 2015 to 2016. The onset of gametogenesis (Gl-G2) was detected for the 2016 to 2017 season in July 2016 at MLV, August 2016 at GLB, and September 2016 at MRN, with 3.6%, 6.7%, and 43.8% of oysters in the early gonad development stage, respectively (Figs. 5A, 6A, and 7A, respectively). A large proportion of late development and ripe oysters (G3-G4) were observed from October 2016 through March 2017 at both GLB and MRN (Figs. 6A and 7A, respectively). Spawned oysters (G5) were first observed in December 2016 at GLB (5.9%) and February 2017 at MRN (23.5%).

The percentage frequencies for each gonad phase at monthly intervals, for all sites, are shown in Figures 5B, 6B, and 7B, respectively. Histological examination of the specimens identified 180 (34.2%) females, 250 (47.4%) males, 2 (0.4%) hermaphrodites, and 95 (18.0%) of indeterminate gender, across all sites. The sex ratio (female:male) for each site was 1:1 at MLV, 1:1.5 at GLB, and 1:2.4 at MRN, with a total sex ratio of 1:1.4 across all sites. Pearson chi-square test showed a significant difference between the proportions of females, males, hermaphrodites, and indeterminate gender across sites ([X.sup.2] = 26.28; df = 6; P < 0.001). At GLB, Pearson chi-square tests showed significant differences between the proportions of females ([X.sup.2] = 23.51; df = 1; P < 0.001), males ([X.sup.2] = 7.54; df = 1; P < 0.05), and indeterminate gender ([X.sup.2] = 34; df = 1; P < 0.001) between the monsoon and dry seasons. Similarly at MRN, Pearson chi-square test showed a significantly higher proportion of indeterminate gender during the dry season compared with the monsoon season ([X.sup.2] = 29.82; df =1; P < 0.001), whereas no significant difference was detected between the proportions of gender between seasons at MLV. Across all sites, no significant differences were detected between gender and oyster size (F = 0.517; df 3/479; P > 0.05 and F = 0.573; df 3/481; P > 0.05, DVM and APM, respectively).

The GI of Saccostrea echinata presented a clear annual cycle (Fig. 8). The GI values fluctuated but remained high (1.94-3.94) from October through April and were low (>l.5) from May through September, across both seasons. The lowest GI value (zero) occurred from May to July 2016 at MRN and the highest (3.94) occurred in October 2016 at GLB. Across all sites, the GI had a strong positive correlation with temperature (r = 0.783; df = 26; P < 0.001) and a moderately positive correlation with rainfall (r = 0.496; df = 31; P < 0.05).

Environmental Data

Annual temperature cycles were significantly different across sites (F = 302.5; df 2/33,108; P < 0.001); however, post hoc Tukey HSD tests showed that temperatures at MRN were driving this difference, because temperatures at MLV and GLB were not significantly different from each other (P > 0.05) (Fig. 9). Annual median temperature fluctuations ranged from 26.3[degrees]C (June 2017) to 31.7[degrees]C (January 2016) at MLV, 25.6[degrees]C (July 2016) to 32.6[degrees]C (January 2016) at GLB, and 25.1[degrees]C (August 2016) to 31.5[degrees]C (February 2016) at MRN (Fig. 9). Temperatures reached a minimum of 16[degrees]C (MLV, August 2016) and a maximum of 48.5[degrees]C (MRN, March 2017) (Fig. 9). Mean temperatures at all sites differed significantly between the monsoon and dry seasons; MLV (F = 1,798; df 1/12,814; P < 0.001), GLB (F= 7,960; df 1/8,149; P < 0.001), and MRN (F = 2,481; df 1/12,142; P < 0.001).

Monthly rainfall patterns were significantly different between sites (Pseudo-F = 21.62; df 2/2,110; P(perm) < 0.001) and mean monthly rainfall ranged from 0.0 to 21.0 mm at MLV, 0.0-22.4 mm at GLB, and 0.0-17.0 mm at MRN (Fig. 10). Significantly higher rainfall was recorded in the monsoon season at all sites (Pseudo-F = 341.09; df 1/2,110; P(perm) < 0.001).

DISCUSSION

This is the first investigation of the exogenous factors influencing reproductive seasonality of Saccostrea echinata in the Northern Territory, Australia. Oyster reproductive strategies vary and can range from clearly defined spawning peaks (Loor & Sonnenholzner 2014), to protracted spawning seasons (Sakuda 1966), and are species-specific (Bayne 1976). Results of this study indicate that the reproductive cycle of S. echinata in northern Australia involves semicontinuous spawning throughout the monsoon season (October-April) and an extended resting phase throughout the dry season (May-September). Although consistent with results for S. echinata in eastern Australia (Lindsay 1994), the results of this study contrast with reports of semicontinuous spawning of 5. echinata in the Philippines (Lopez & Gomez 1982) and of two spawning peaks for this species in Guam (Braley 1984). Whereas differences in reproductive strategies of oysters at different sites within their natural range have been previously reported (Loosanoff & Nomejko 1951), it is possible that misalignment of the results of this study with those of Lopez and Gomez (1982) and Braley (1984) may be due to misidentification of S. echinata, in the later studies because the taxonomic status of this oyster is poorly defined. Morphological identification of Saccostrea spp. is extremely difficult (Sekino & Yamashita 2016) and molecular data for S. echinata are only recently become available (McDougall 2018).

Despite disparate populations of some oyster species showing different reproductive patterns, such as Crassostrea virginica (Loosanoff & Nomejko 1951, Aranda et al. 2014) and Crassostrea gigas (Chavez-Villalba et al. 2002), there is obvious advantage in geographically close populations having synchronized reproductive cycles (Bayne 1976). Oysters from all three locations across northern Australia, sampled in this study, showed a synchronized reproductive pattern. This suggests that the exogenous factors driving reproduction are similar across the spatial scale of the sampled sites (up to 580 km). In Queensland, eastern Australia, Saccostrea echinata begins spawning in December (Lindsay 1994), 3 mo later than reported in this study. These two studies show that S. echinata do not have a synchronized reproductive pattern across the broader northern Australian coastline at a larger spatial scale (thousands of kilometers). These findings conform to the theory that the reproductive patterns of marine invertebrates are synchronized by exogenous factors, which vary with season and latitude (Olive 1995).

Condition index of oysters is a useful tool for macroscopic assessment of the quality and yield of oyster meat, and it is often used to determine marketability (Mason & Nell 1995). It may be calculated using either dry tissue weight or wet tissue weight (Hopkins 1949, Lawrence & Scott 1982). Although CI calculated using wet weight is often preferred because of its simplicity, speed, and the ability to use large sample sizes (Baird 1958), it was necessary in this study because it allowed subsequent histological analysis of tissue samples (Dove & O'Connor 2012). The CI values obtained in this study showed little variation, and the variation that was recorded did not relate to seasonal or reproductive changes. It is possible that calculation of CI using dry weight not wet weight may have allowed finer-scale interpretation of oyster condition in this study.

Influence of Temperature on Reproduction of Saccostrea echinata

Most studies investigating the influence of temperature on reproductive cycles of rock oysters have reported on seawater temperature only; however, in the tropics, water temperature generally shows low seasonal variation (Fournier 1992, Paixao et al. 2013, Loor & Sonnenholzner 2014). Rock oysters are intertidal organisms and are generally exposed to air during low tide. The temperature values reported in this study were generated from intertidal loggers, deployed within wild oyster populations on rocky intertidal outcrops; they accounted for both water temperature and air temperature in the range of values recorded. The temperature ranges recorded in this study are therefore more extreme (e.g., 14[degrees]C-48[degrees]C, across all sites) than those previously reported in similar studies, such as 29[degrees]C-33[degrees]C (Fournier 1992), 28[degrees]C-30[degrees]C (Paixao et al. 2013), and 2O[degrees]C-32[degrees]C (Rodriguez-Jaramillo et al. 2008).

Temperature is generally recognized as the most important exogenous factor affecting reproduction in temperate rock oyster species (Orton 1920, Fabioux et al. 2005, Lucas 2012). Temperature has also been reported as an important factor in reproduction of tropical oyster species. In Striostrea prismatica, along the southern coast of Ecuador, for example, gametogenesis is associated with thermal cycles (surface seawater temperature) and GI values peak in the warmer summer months (January-February) (Loor & Sonnenholzner 2014). Temperature similarly seems to be an important regulatory factor in reproductive seasonality in Saccostrea echinata, with both this study and Lindsay (1994) reporting strong, positive correlations between GI and temperature (r = 0.783 and r = 0.894, respectively).

Influence of Rainfall on Reproduction of Saccostrea echinata

In the tropics, rainfall is typically considered a key exogenous factor affecting reproduction of rock oysters because the monsoon significantly reduces salinity in coastal waters. In northern Australia, monsoonal rains can occur from October through April (Holland 1985), and inshore salinity can drop to as low as four (S. Nowland, unpublished data). Rapid reduction in salinity has been associated with spawning induction in a number of tropical rock oyster species, including S. prismatica along the Pacific coast of Costa Rica (Fournier 1992) and Saccostrea echinata in northern Australia (Southgate & Lee 1998). This seasonal reduction in salinity is reflected in improved growth and survival shown by S. echinata larvae within an optimal salinity range as low as 23 (unpublished data). The effect of reduced salinity on gonad development and maturation in tropical oysters, however, is less clear and may reflect concomitant changes in nutrient levels (Angell 1986, Fournier 1992). Correlation between salinity and gonad maturation has been reported for Crassostrea gasar in Brazil (Paixao et al. 2013), and rainfall showed moderate, positive correlation with GI (r = 0.496), in this study.

In northern Australia, a geographically broad and extensive annual phytoplankton bloom occurs at the onset of the monsoon season, as water temperature begins to rise. Both Taylor et al. (2016) and Munksgaard et al. (2017) reported this event in September 2015 and September 2013, respectively, at South GLB (site GLB). These blooms are likely to be a major driver of reproductive seasonality in Saccostrea echinata at the sites sampled in this study. This September algal bloom correlated with the rapid increase in GI at all sample sites in this study, and it is likely that increased nutrient availability provided by the bloom supported late gametogenesis recorded from September to October. It is also possible that, besides driving gonad development, bloom events may provide a spawning signal assuring abundant food for resulting larvae (Starr et al. 1990, Aji 2011). Correlation between phytoplankton blooms and the occurrence of pelagic larvae has long been recognized (Bayne 1983, Angell 1986). Starr et al. (1990) documented the positive spawning response of sea urchins and mussels (Mytilus californianus) to phytoplankton and reported that blooms supported favorable conditions for larval growth and survival. Although the study data indicate spawning of oysters immediately after the annual phytoplankton bloom in September, further research is warranted to better understand the role of this bloom event on oyster reproduction and spawning in northern Australia.

Gender Ratios

Information of sex determination mechanisms for Saccostrea echinata does not exist. Based on previous findings for both Saccostrea and Crassostrea (Dinamani 1974, Guo et al. 1998), however, it might be expected that S. echinata is a protandric, dioecious species with low levels of functional hermaphroditism as reported for Crassostrea glomerata (Dinamani 1974), which is now considered to be in genus Saccostrea (Salvi et al. 2014). If S. echinata is protandric, a relationship between oyster size and gender would have been expected in this study, with males predominating smaller sizes. Despite this, however, no evidence was found to indicate protandry, with oyster size (DVM and APM) not significantly related to gender. Evidence was found to support dioecy in S. echinata with a female: male sex ratio of 1:1.4, across all sites. Furthermore, the frequency of hermaphrodites (0.4%) found is comparable to that reported for Saccostrea glomerata (0.6%) (Dove & O'Connor 2012) and Saccostrea cucullata (0.7%) (Braley 1982). The findings of this study support the supposition that hermaphroditism is a rare but consistent feature of reproduction in rock oysters (Guo et al. 1998).

Applications of the Results of This Study

The results of this study show that Saccostrea echinata populations in the Northern Territory, Australia, display clear reproductive seasonality. Mature broodstock can be collected from October through April and oysters spawn throughout the monsoon season. Gametogenesis was strongly correlated to intertidal temperatures and moderately correlated to rainfall. It is likely that a large-scale annual phytoplankton bloom provides resources for late gametogenesis and that rainfall, and possibly increased phytoplankton availability, initiates spawning activity. The information generated in this study has value in a number of potential applications: (1) knowledge of reproduction peaks can inform both the timing of broodstock collection from the wild for hatchery production (Nowland et al. 2018) and the timing of harvest to maximize marketability; (2) the key environmental factors influencing gonad maturation can be used in broodstock conditioning for hatchery production; (3) baseline information and detailed reporting of reproductive stages for 5. echinata will support similar research with this and other tropical rock oyster species; and (4) improved knowledge of the biology of S. echinata provides a broader basis for developing its potential as a commercial aquaculture species.

ACKNOWLEDGMENTS

This study was conducted within the Northern Territory Government "Tropical Rock Oyster Aboriginal Economic Development Program." We thank the Warruwi community of Goulburn Island, the Crocodile Island Rangers of Milingimbi Island, and the Tiwi Marine Rangers of Melville Island for supporting this project with regular collection of wild oysters. We also recognize the significant support provided by staff of the Darwin Aquaculture Centre, and we particularly thank Cameron Hartley, Shannon Burchert, and Eloise Wigger for their assistance with sample processing. We are also very grateful of the histology processing work performed by staff at the Berrimah Veterinary laboratory, and we particularly thank Kitman Dyrting.

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SAMANTHA J. NOWLAND, (1,2*) WAYNE A. O'CONNOR, (3) SHANE S. PENNY (1) AND PAUL C. SOUTHGATE (4)

(1) Aquaculture Unit, Department of Primary Industry and Resources, Northern Territory Government, GPO Box 3000, Darwin, NT 0801, Australia; (2) School of Science & Engineering, University of the Sunshine Coast, 90 Sippy Downs Drive, Sippy Downs, QLD 4556, Australia; (3) NSW Department of Primary Industry, Port Stephens Fisheries Institute, Taylors Beach, NSW 2316, Australia; (4) Australian Centre for Pacific Islands Research and School of Science and Engineering, University of the Sunshine Coast, Maroochydore, QLD 4556, Australia

(*) Corresponding author. E-mail: samantha.nowland@nt.gov.au

DOI: 10.2983/035.038.0109
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Author:Nowland, Samantha J.; O'Connor, Wayne A.; Penny, Shane S.; Southgate, Paul C.
Publication:Journal of Shellfish Research
Article Type:Report
Geographic Code:8AUST
Date:Apr 1, 2019
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