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Gonad development of the pen shell Atrina pectinata from Shandong Province, China.

ABSTRACT The processes of gametogenesis, development, and degeneration, together with the gonad fatty acids, of the pen shell Atrina pectinata were studied. The results showed that water temperature is the key factor affecting gonadal development. The gonad started to develop and differentiate at 6-7[degrees]C, with fast development of both the visceral mass and the gonad when the temperature increased to 11-12[degrees]C. The gonad index peaked at approximately 21[degrees]C, which suggested that 6- 7[degrees]C is the threshold for gonad development and that 21 [degrees]C is the optimum temperature at which broodstock will mature. The gonad fatty acid 18:1 n-9 correlated remarkably with the condition and gonad indices, which might be indicative of the maturity of the gonad of A. pectinata. From the perspective of nutritional composition, Pavlova sp. and Chroococcus sp. were thought to be the most appropriate feed for A. pectinata broodstock cultivation.

KEY WORDS: pen shell Atrina pectinata, gonad index, fatty acid, temperature


The pen shell Atrina pectinata (Linnaeus), belonging to the family Pinnidae, is widely distributed along the Indo-West Pacific coasts of Japan, Korea, China, Malaysia, and northern Australia (Wang 1997). It is usually found in muddy to sandy sediment habitats from the lower level of the intertidal zone to the sublittoral zone to a depth of 50 m (Wang 1964).

As a result of the intensive harvest of this species during the first few years of the 21st century, the numbers of Atrina pectinata in the wild were reduced substantially. Official statistics show that the production of A. pectinata in China in 2004 had decreased drastically by 86% compared with 2003, and that the levels have shown little recovery since then (Ministry of Agriculture, People's Republic of China 2003-2011). In Japan, the mass mortality of pen shell during 2003 and 2004 was attributed to outbreaks of disease (Maeno et al. 2006). However, despite these natural diseases, overharvesting and the destruction of its habitat are thought to be the most important factors influencing the occurrence of this species in China.

An effective measure for the restoration of stock abundance is to establish aquaculture techniques for seed production. To this end, understanding gametogenesis, the reproductive cycle, and broodstock cultivation conditions for this species is vital. Wang et al. (2000) and Chung et al. (2006) studied gonad development and gametogenesis of wild Atrina pectinata in the South China Sea and South Korea, respectively. Maeno et al. (2009) investigated the maturation process of A. pectinata under artificial rearing conditions. However, the water temperature in these areas was warmer than in the north China Sea, and temperature data were not collected carefully; thus, the relation between gonad development and temperature is still unclear.

Although juveniles of Atrina pectinata have been reared successfully in the laboratory (Kawahara et al. 2004, Allen 2011) and for large-scale production in 2004 to 2006 (Yu et al. 2007), the larval rearing process and the survival rates during the pelagic period were not stable for large-scale production. Despite these studies, many problems remain with regard to broodstock cultivation and relations among temperature, nutrition, and gonad development, which are important for broodstock cultivation and seed production.

In terms of the relation between nutrition and gonad maturation of Atrina pectinata, Yurimoto et al. (2005) studied the relation between gonad maturation and glycogen contents of the adductor muscle, and suggested that glycogen content is a useful parameter for characterizing gonad development in A. pectinata, and could function as an energy resource for sexual maturation; however, other than this research, there are no data available relating to gonadal nutrition, which can reflect gonad maturation more directly.

In this study, Atrina pectinata were sampled in the shallow sea of Rizhao, where the temperature was monitored almost every day, and the process of gonad development was studied through morphological and histological observations. In addition, the composition of gonad fatty acids (FAs) was measured at all developmental stages, and correlation analysis was used to study their changes in relation to gonad development and spawning, with expectation of finding an FA that is indicative of the ripeness of the gonads of A. pectinata. Such information would be very useful for the aquaculture industry.


Collection and Treatment of Samples

Samples of Atrina pectinata were collected once or twice a month (during a reproductive season) from December 2009 to November 2010 by diving down to approximately 20-30 m in the shallow sea of Rizhao (35[degrees]30' N, 119[degrees]50' E), Shandong Province, China. The bottom water temperature was measured every 1-2 days near the coast, where the water was more than 5 m deep. This temperature was shown to be within 0.2[degrees]C of the in situ temperature. Thirty samples were brought to the laboratory alive, ensuring 10-15 males and females were sampled each time, and their shell height, shell length, total wet weight, the weight of flesh (body weight excluding the shell), and the wet weight of the gonads were measured. The gonads were then observed under a microscope, and parts were fixed in 5% neutral formaldehyde solution and sliced to produce 5-[micro]m-thick samples that were then stained using the hematoxylin-eosin stain. The remaining gonads were kept in a freezer at -80[degrees]C and then used to determine the content of gonad FAs.

Oocyte Diameter in Ovaries at Different Developmental Stages

The slices were observed using an Olympus-C21 microscope, and only the oocytes cut through the nucleus were measured. The geometric mean of the length and width of more than 15 oocytes from 3 different individuals was used to represent oocyte size.

Condition and Gonad Indices

The condition index (CI) was calculated as CI = F/[square root of SH x SL], where SH is the shell height, SL is the shell length, and F is the flesh wet weight. In this newly constructed equation, the geometric means of shell height and shell length were used to represent the CI better. In addition, when measuring the flesh weight, there is a lot of coelomic fluid in the lumen of Atrina pectinata, and it is hard to keep this fluid intact. Therefore, the mantle was punctured before weighing to remove the fluid. The gonad index (GI) was obtained subsequently by the equation GI = G x 100%/F (Barber and Blake 2006), where F is flesh wet weight and G is gonad wet weight.

Determination of the Content of Gonad FAs

Female Atrina pectinata were sampled 10 times from December 2009 to January 2011. Five to 8 gonad samples of the same batch were freeze-dried each time, ground using a pestle and mortar, and then mixed each other. Then, the content of 23 different detected gonad FAs, including 12:0, 14:0, 15:0, 16:0, 16:1 n-9, 16:1 n-7, 16:ln-5, 16:2n-4, 18:ln-9, 18: ln-7, 18:2n-6, 18:2n-4, 18:3n-3, 18:4n-3, 20:0, 20:ln-9, 20:ln-7, 20:2n-6, 20:3n-6, 20:4n-6, 20:4n-3, 20:5n-3, and 22:6n-3, was determined by high-performance liquid chromatography according to the methodology of Liu et al. (2011). The data of FA content of marine microalgae were collected from published papers. The shorthand notation used in identifying FAs is C: Bn-A, where C is the chain length, B is the number of double bonds, and A is the position of the ultimate double bonds.

Statistical Analysis

Pearson's 2-variable correlation analysis was used to determine the relation between indexes (P < 0.05 or P < 0.01) of oocyte diameter, GI, CI, and temperature, and also the FA content among different microalgae and Atrina pectinata. These statistical analyses were performed using SPSS software v.17.0.


Morphological Observations

The pen shell Atrina pectinata is an infaunal bivalve found in muddy to sandy substrates. In winter, approximately one third to one half of its shell appears above the seabed surface; however, as the temperature increases, the animal becomes more buried in the substrate. By the summer, the entire body is buried. This pen shell is dioecious, with its gonads closely attached to the digestive gland. The mature ovaries are orange and the mature testes were bright ivory. In the 191 samples that we collected from March to August 2010, there were 97 females and 94 males, which suggested that, in the wild, the sex ratio is nearly 1:1. Forty 6-7-mo-old juvenile A. pectinata with a shell length of 100 [+ or -] 5 mm (mean [+ or -] SD) were collected in February, 2012, and their gonads had begun to develop. More than half their gonads were sexually recognizable, which suggests that individuals that are 1 y old are sexually mature.

Gonadal Development

The gonads are comprised of follicles, gonad tubules, and gonoducts. The follicles were cystiform, with a follicular wall and follicular lumens. The early-stage germ cells were attached to the follicular wall, and the mature ones were in the lumens. The sex of the broodstock was recognizable based on the color of the gonads, apart from when the gonads had degenerated. With reference to Maeno et al. (2009) and the observation of oocytes, GIs, CIs, and spawning, we divided the development process into 5 stages: resting stage (September to November), developing stage (December to May), mature stage (May to July), partially spawning stage (July to August), and spent stage (August to October).

Testes Development

Resting Stage

During the resting stage, testes had almost disappeared and were not recognizable.

Developing Stage

During the developing stage, the follicles were filled with spermatogonia and spermatocytes that had not yet begun to differentiate into spermatozoa. The follicular diameter was approximately 150-200 [micro]m. The spermatogonia, with a diameter of 4-5 [micro]m, were attached to the follicular walls, and the spermatocytes, with the diameter of 2.5-3 [micro]m, were in the center of the follicular lumens (Fig. 1A). The testes were attached to the end of the visceral mass close to the posterior adductor muscles; the profile of the gonad at this stage was blurred.

Mature Stage

During the early June, the testes were bright ivory and almost surrounded the visceral mass. The volume of the follicles was much bigger than before and they were 300-600 [micro]m in diameter. Most of the spermatogonia and spermatocytes had differentiated into spermatozoa, except for a few spermatogonia that were still attached to the follicular walls. The spermatozoa at this stage were not yet mobile and remained in the follicles (Fig. IB).

Partially Spawning Stage

At the end of June, the germ cells completed the process of differentiation. There were still a few spermatogonia attached to the follicular walls, whereas spermatocytes were rarely found in the follicles. Most of the inner space of the follicle was full of mature spermatozoa, which had nuclei with an average diameter of approximately 1.6 [micro]m. Empty holes were observed in the follicles of partially spawned testes. At this stage, the volume of the follicles was the largest of all the stages, and the follicle wall was thin and not easy to recognize. The partially spawning testes were darker than the unspawned testes (Fig. 1C).

Spent Stage

In August, the testes turned dark yellow and grainy, and they began to degenerate and atrophy. The volume of follicles decreased and the gap between follicles became wider. In the follicles, there were a few spermatogonia and spermatozoa remaining (Fig. ID).

Ovary Development

Resting Stage

Similar to the testes, the ovaries had degenerated and could not be recognized during most of this stage.

Developing Stage

During November to April, the gonad of Atrina pectinata had a moderately developed form. It became more distinguishable because the ovaries had turned dark red. The GI and CI did not change much from November to April, with the exception of the size of oocytes, which increased rapidly at the end of March, when the temperature began to increase from its lowest point. The oogonia and oocytes were attached to the walls of follicles and there were interspaces among and in the follicles. (Fig. IE).

Mature Stage

As shown in Figure 2, when the water temperature increased to 6-7[degrees]C in April, the oocytes grew rapidly, almost reaching their mature size in May. However, the GI did not increase simultaneously with oocyte size (Fig. 3). When the water temperature reached 11[degrees]C in May, the CI started to increase quickly. Similarly, the GI started to increase significantly in June, when the water temperature reached 16-1 S[degrees]C, and peaked at the end of June, indicating that the ovaries were mature and ready to spawn (Fig. 1F).

Partially Spawning Stage

During late June to late July, when the average water temperature reached 21[degrees]C, Cl and oocyte diameter peaked (Figs. 2 and 3), followed by a peak in GI when the temperature reached 22-23[degrees]C (Fig. 3). At this time, the broodstock began to spawn partially and the follicles were partially empty; some of these had shrunk, which indicated that mature oocytes had been spawned (Fig. 1G).

Spent Stage

In August, the follicular walls wrinkled and shrunk, and nearly all the mature oocytes had been spawned. Some of the oocytes that were left had broken up and were then resorbed (Fig. III).

Variation in Oocyte Diameter

The average diameter of oocytes is a key index to estimate the degree of maturity of ovaries. In the current study, oocyte diameter was determined by measuring the diameter of oocytes in tissue slices; thus, the diameter was not an exact representation of the actual condition, because the oocytes shrank during fixation. However, the degree of variation indicated that the diameter did not change during the long-term moderate developing stage (November to March) when the temperature was less than 6[degrees]C, but increased quickly during the mature stage (April to May) when the temperature reached 11[degrees]C. The oocytes peaked in size as the temperature reached 21[degrees]C. Between 11[degrees]C and 18[degrees]C, oocyte diameter increased the fastest (Fig. 2). Through Pearson's correlation analysis, we found that the increase in oocyte diameter correlated significantly and positively with water temperature (r = 0.928, P < 0.01). Consequently, water temperature might be a key factor that stimulates germ cell development.

Condition and Gonad Indices

When the water temperature reached 6-7[degrees]C in April, the Cl increased rapidly, whereas the GI did not. In May, the water temperature was mor than 11[degrees]C; both indices increased quickly, and nutrients accumulated in the somatic tissues. Both indices peaked at the end of June almost simultaneously, with a water temperature of 21-22[degrees]C. Then, the water temperature continued to increase, but both indices started to decrease. The gonads degenerated quickly from the middle of August to the middle of September, such that, by the end of September, it was almost impossible to distinguish between the sexes of Atrina pectinata until the end of the resting stage.

Based on Pearson's correlation analysis, when the water temperature was less than 23[degrees]C (from December to early July of the following year), both GI and CI correlated significantly and positively with water temperature (r = 0.932. P - 0.001; r = 0.946. P - 0.000, respectively).

Variation in Gonad FAs in Different Developmental Stages

The average total content of gonad FAs of Atrina pectinata was 21.0 [+ or -] 2.2% (mean [+ or -] SD). It peaked in mid May (24.2%) and decreased to its lowest level during the spent stage after spawning (16.2%); however, no samples were collected during the resting stage.

Results (Table 1) showed that 7 types of FA comprised more than 3% of the total gonad FA content (mean [+ or -] SD). They were 16:00 (33.92 [+ or -] 1.9%), 20:5n-3 (EPA; 18.07 [+ or -] 2.0%), 22:6n-3 (DHA; 14.52 [+ or -] 1.6%), 18:ln-9 (6.74 [+ or -] 1.7%), 18:ln-7 (4.92 [+ or -] 0.7%), 16:1 n-7 (4.22 [+ or -] 0.8%), and 14:00 (3.08 [+ or -] 0.4%). The correlation between the content of each type of gonad FA (Table 1) and the water temperature, GI, and CI was analyzed. The content of 15:00 correlated significantly and positively with water temperature (r = 0.780, P < 0.01), GI (P < 0.05), and CI (r = 0.671, P < 0.05). 18:1 n-9 also correlated significantly and positively with GI (r = 0.799, P < 0.01) and CI (r = 0.732, P < 0.05). 18:2n-6 correlated significantly and positively with GI. However, 18:2n-4 (r = -0.937, P < 0.01), 20: In-7 (r = -0.929, P < 0.01), 16:1 n-7 (r = -0.919, P < 0.01), and 20:5n-3 (EPA; r = -0.889, P < 0.01) had significant negative correlations with water temperature.


Time Point and Threshold Temperature for Gonad Development

The time points of gonad development were different from the results of Maeno et al. (2009), Chung et al. (2006), and even Qiu et al. (2000), because the sea area sampled was also different. In the study by Maeno et al. (2009), gonads started to develop in December to February, with a water temperature of approximately 15[degrees]C. Chung et al. (2006) reported gonadal development from November to the following March, with a water temperature of approximately 11[degrees]C, and Qiu et al. (2000) reported gonadal development in March, when sea temperatures were less than 10[degrees]C. In the current study, we found that the CI and oocyte diameter started to increase significantly when the water temperature reached 6-7[degrees]C (Table 2).

The fastest period of gonadal development in the research of Maeno et al. (2009) started in May, with a water temperature of nearly 20[degrees]C; in Chung et al. (2006), in April (15.2[degrees]C); and in Qiu et al. (2000), in May (11[degrees]C). In the current study, the gonads developed the quickest when water temperature was more than 11[degrees]C. When the water temperature reached 1618[degrees]C in June, oocytes had almost reached mature size; however, GI continued increasing rapidly until the water temperature reached 22[degrees]C.

The gonad matured and partially spawned in the research of Maeno et al. (2009) in August, with a water temperature of 25[degrees]C; in Chung et al. (2006), in June (20[degrees]C); and in Qiu et al. (2000), in July (20-24[degrees]C). In the current study, the results showed that partially spawning was from the end of June to the beginning of July, when the water temperature was 21-23[degrees]C, indicating that gonads could mature with a water temperature of 21[degrees]C, which is consistent with the result of the study by Qiu et al. (2000).

The spent stage is during late August in the Rizhao sea area, which is approximately 15 days earlier than in the northern part of the Shandong sea area. The pen shell Atrina pectinata from the Rizhao sea area reached maturity only once a year, and spawned from the end of June to the beginning of August. The gonads then degenerated significantly in September and October. However, in the Zhanjiang sea area, there was no significant spent stage between 2 spawning peaks in May and October (Wang et al. 2000).

To conclude, the time points and threshold temperatures discussed here are detailed in Figure 4. Oocyte diameter and CI start to develop at 6[degrees]C, and then speed up their development at 11[degrees]C. The GI starts to develop at 11[degrees]C, and then speeds up at 16[degrees]C. During the period of temperature stabilization at 16-18[degrees]C, all 3 values developed quickly, which suggests that 16-18[degrees]C is the best temperature for broodstock cultivation of Atrina pectinata. With regard to gonadal development, temperature has an important role, according to our study, although this is not always the case. For example, in the research of Maeno et al. (2009), the lowest temperature of the researched sea area was 15[degrees]C, and they suggested that other environmental factors, such as food richness and hours of sunshine, stimulated gonad development.

Relation Between Gonad FA Content and Gonad Development

From December to the following May, before the water temperature reached 11 [degrees]C, the GI and CI did not vary significantly. However, the total content of gonad FAs increased from 199,914-222,519 pg/g (dry weight) during this period, and peaked at 241,790 pg/g in May. This indicated that FAs accumulated in the gonad during the early developing stage. During the following maturation stage (May to July), the content of all the major FAs (>3% dry weight) decreased. There might be 2 main reasons account for this: first, the FA supply becomes exhausted during the gonad maturation process as an energy resource; second, the eggs, which contain more FAs than other nutrients, were eliminated, thus removing most of the FA content.

During the partially spawning stage (July to August), the amount of all types of gonad FAs declined. This might be because of the large amount of eggs being shed during the spawning process; we can also infer this from the fact that the FA content in oocytes was greater than in peripheral tissue in the gonad. As a result, the well-developed gonad contained a greater proportion of FAs. Throughout the entire process of gonad development, 18:ln-9 correlated significantly an dpositively with GI. Freites et al. (2010) also considered that 18: ln-9 correlated significantly and positively with the relative frequency of ripe gonads. Therefore, the content of 18:1 n-9 could be used to estimate the degree of ripeness of the gonads in this species.

Gonad FA and the Common Marine Microalgae FA

Data showing the FA content of 12 species of marine microalgae (Synechococcus sp., Isochrysis galbana, Pavlova sp., Phaeodactylum tricornutum, Porphyridium cruentum, Rhodomona sbaltica, Oocystis sp., Pseudokirchneriella subcapitata, Tetraselmis sp., Tribonema sp., Nannochloropsis oceanica, Chroococcus sp.) were collected from Patil et al. (2007). We then analyzed the FA content of these microalgae and compared it with that of the pen shell gonads using Pearson's correlation analysis. Of the 23 types of FAs measured in Atrina pectinata, 14 also occurred in the microalgae (12:00, 14:00, 16:00, 20:00, 16:ln-7, 18:ln-9, 20:ln-9, 18:2n-6, 18:3n-3, 18:4n-3, 20:2n-6, 20:4n-6, 20:5n-3, 22:6n-3).

The results showed that the FAs of 5 species of microalgae (Pavlova sp., 0.757 and 0.002; Chroococcus sp., 0.670 and 0.009; Porphyridium cruentum, 0.605 and 0.022; Nannochloropsis oceanica, 0.538 and 0.047; Phaeodactylum tricornutum, 0.541 and 0.046; numbers are r and P values by Pearson correlation analysis) had a significant correlation with the pen shell gonad FAs. From a nutritional composition viewpoint, Pavlova sp. and Chroococcus sp. are thought to be the best food sources for Atrina pectinata broodstock cultivation among the 12 species of marine microalgae.


It is suggested on the basis of our survey results that the most appropriate time to collect broodstock is when the temperature reaches 16-18[degrees]C. After collection, the rearing temperature should not be increased quickly, but kept at 1618[degrees]C for several weeks. In contrast, adults should be kept in seawater at 21[degrees]C until they have spawned. The gonads were rich in many kinds of FAs, of which 18:ln-9 showed close correlation to the CI and GI; therefore, it could be used as an indication of the ripeness of the gonads of Atrina pectinata. During broodstock cultivation, the microalgae Pavlova sp. and Chroococcus sp. could be a suitable potential food source for A. pectinata.


This work was funded by the National Key Technology R&D Program (2011BAD13B01 & 2011BAD45B01), the External Cooperation Program of Chinese Academy of Sciences, and the National Marine Public Welfare Research Project (201305043).


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Institute of Oceanology, Chinese Academy of Sciences, Nanhai Road 7, Qingdao, 266071, PR China

* Corresponding author. E-mail:

DOI: 10.2983/035.033.0215


The content of different fatty acids in the ovary of Atrina pectinata
(in micrograms per gram dry weight) across the sample period.

                              Sampling date

Type of
fatty acid   Dec 25    Mar 20     Apr 5     May 9    May 20

12:0             72        79        68        91        78
14:0          6.475     7,121     7,320     7,130     7,367
15:0            807       816       870       943       814
16:0         63,632    70,681    71,828    83,541    82,145
20:0            419       612       643       770     1,274
16:1 n-9        127       115       108       114       156
16:1 n-7      9,439    11.083    11,019    10,597     9,305
16:1 n-5        696       797       873       861     1,056
18:1 n-9     10,538    12,096    11,835    14,597    17,043
18:1n-7      10,887    11,820    13,217    13,963     9,308
20:1 n-9      3,411     3,558     3,882     4,275     3,787
20:1 n-7      4.556     4,150     4,655     4,596     3,009
16:2n-4         176       175     1,012       984       832
18:2n-4       1,352     1.472     1,288     1,385     1,056
18:2n-6       1,689     2,001     2,423     2,637     2,276
20:2n-6       1,740     1,734     1,814     1,981     1,816
18:3n-3       2,317     2,659     2,747     2,969     2,450
20:3n-6       1.140     1,234     1,302     1,221       589
18:4n-3       4,269     5,395     5,670     7,092     5.217
20:4n-6       3,346     3,126     3,330     3,357     2,070
20:4n-3       2,247     2,313     1,959     2,369     2,973
20:5n-3      42,795    41,850    42,905    43,943    41,481
22:6n-3      27,783    29,399    31,749    32,374    34,111
[SIGMA]      199,914   214,288   222,519   241,790   230,211

                              Sampling date

Type of
fatty acid   Jun 23     Jul 4    Jul 15    Aug 12    Jan 10

12:0             74        59        62        53        64
14:0          6,785     6,549     5,959     3,351     7.050
15:0            941       944       924       944       760
16:0         77,913    74.165    69,207    54,298    65,617
20:0            986       964       806       284       419
16:1 n-9        165       131       144       235       120
16:1 n-7      8,144     7.756     7.267     4,149    10,892
16:1 n-5        930       889       713       593       645
18:1 n-9     17,329    16,667    16,319    14,806     8,732
18:1n-7       9,167     9,366     9,417     6,392    10,428
20:1 n-9      2,990     3,275     3,010     2,916     3,762
20:1 n-7      2,351     2,652     2,524     1,728     4,770
16:2n-4         770       726       698       524     1,525
18:2n-4         876       869       888       515     1,741
18:2n-6       3,050     3,289     3,075     1,526     3,032
20:2n-6       1,757     1.897     1,646     1,184     2,813
18:3n-3       3,025     3,059     2,951     2,587     3,008
20:3n-6         657     1.056     1,046       264       923
18:4n-3       5,608     5.493     5,238     4,897     6,775
20:4n-6       2,092     2,216     2,307     1,859     3,010
20:4n-3       3,044     3,004     2,748     4,488     3,501
20:5n-3      35,996    35,216    30,832    24,216    42,099
22:6n-3      30,706    29,955    25,872    30,346    30,658
[SIGMA]      215,356   210,197   193,653   162,156   212,345

positively with water temperature (r = 0.932, P = 0.001;
r = 0.946, P = 0.000, respectively).


Different developmental stages and corresponding water
temperature as reported by different articles.

Reference        Developing stage       Mature stage

Qiu et al.            March,            May-June, 11
(2000)             <10[degrees]C        21[degrees]C

Chung et al.     November-March,      April-June, 15.2-
(2006)             ~11[degrees]C       22.4[degrees]C

Maeno et al.    December-February,      May-August,
(2009)            ~ 15[degrees]C        20[degrees]C

Current study    November-April,       May-June. 11 -
                   ~6[degrees]C         21[degrees]C

Reference         Spawning stage       Spent stage

Qiu et al.       July-August, 20-       September
(2000)             24[degrees]C

Chung et al.       June-July,            August
(2006)            ~20[degrees]C

Maeno et al.    August-September,        August
(2009)             25[degrees]C

Current study     June-July, 21-        August,
                   23[degrees]C       >24[degrees]C

Reference          Sample site

Qiu et al.      38[degrees]14' N-
(2000)           38[degrees]22' N

Chung et al.    36[degrees] 16' N-
(2006)           36[degrees]19' N

Maeno et al.    32[degrees]46' N-
(2009)           32[degrees]50' N

Current study   35[degrees]22' N-
                 35[degrees]28' N
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Article Details
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Author:Qiu, Tianlong; Zhang, Tao; Bai, Yucen; Xue, Dongxiu; Pan, Yang
Publication:Journal of Shellfish Research
Article Type:Report
Geographic Code:9CHIN
Date:Aug 1, 2014
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