Printer Friendly

Growth of winged pearl oyster (Pteria Penguin) juveniles: a comparison of wire collector culture and circle net culture.

ABSTRACT The aim of this study was to identify effective techniques for the culture of the winged oyster (Pteria penguin) by comparing the growth and mortality of juveniles cultured on a self-designed wire collector and in traditional circle nets. The juveniles were hatchery reared, nearly 5 mo old, and were cultured in Li'an Lagoon, Hainan Island, China. The mean shell height (SH) and total weight (TW) of the juveniles was 26.06 [+ or -] 3.43 mm and 5.85.88 [+ or -] 2.258 g, respectively. They were held for 7 mo in suspended culture either on self-designed wire collectors or in circle nets. The collector was made of galvanized seizing wire, consisting of a top circle, a bottom circle, and 3 pillars between the 2 circles. Every collector was settled with approximately 150 spat and hung naturally in the sea. The oysters cultured in circle nets had three stocking densities: 10 juveniles (D10), 20 juveniles (D20), and 30 juveniles (D30) per net. Juveniles held on wire collectors and in D10 circle nets showed the greatest growth during the experiment, and had significantly greater shell height (SH), maximum diagonal length, hinge length, and TW than oysters in other densities. Oysters in D30 showed the lowest mean SH and maximum diagonal length, hinge length, and TW. Mortality ranged from 3.33% in D10 to approximately 17% for oysters in D30 and on wire collectors. When other factors such as cost of equipment, labor, and ease of construction were considered along with growth and survival, the method of natural hanging on a wire collector is highly advisable in Li'an Lagoon because this method takes advantage of the strong byssi of winged oysters, substantially reduces cost, is easy to construct, and promotes increased growth. Although the loss of oysters was relatively high, it was balanced positively by growth rate and cost reduction, because the spat are hatchery produced and easily available.

KEY WORDS: pearl oyster, Pteria penguin, growth, mortality, self-designed collector, stocking density

INTRODUCTION

The pearl oyster Pteria penguin occurs mainly along tropical and subtropical coasts and is distributed in Southeast Asia, Australia, and some Pacific island nations (Southgate 2008). As a member of the winged pearl oysters, it is the most widespread cultured species, cultured in China, Japan, Australia, the Philippines, Indonesia, Thailand, Vietnam, and the Kingdom of Tonga for the production of large and valuable half-pearls (ma be pearls) (Southgate 2008).

In China, Pteria penguin is increasing in importance with the decline of the traditional cultured marine pearl industry of Akoya pearl production. In recent years, Akoya pearls produced by Pinctada fucata martensii have decreased both in quantity and quality as a result of the inbreeding depression of P. fucata martensii (Gu et al. 2011) and pollution of the environment (Zhang 2007). The market of Akoya pearls have shrunk dramatically recently and a case in point is in Hainan Province, where its production has declined from nearly 1,000 kg in 2007 to less than 150 kg in 2011, as estimated by local producers.

One remedy for the decline of Akoya pearl oysters is to develop culture methods for other species of pearl oysters, and Pteria penguin is a suitable candidate. Currently, mabe pearl production techniques are mature and applied commercially on a large scale in China, including the Guangdong, Guangxi, and Hainan provinces. Of the 3 provinces, Hainan has the largest production scale, with approximately 3,000,000 oysters used mainly for the production of mabe pearls, and a small proportion used for the experiment of free round pearl production.

Despite its wide distribution and growing importance in production, Pteria penguin has received relatively little research attention and there is a dearth of English literature relating to its nursery and grow-out culture methods (Southgate 2008), with the exception of the work by Beer (1999) and Milione and Southgate (2012). The former reported the influence of protective mesh on the growth of P. penguin juveniles and the prevention of predators; the latter compared the growth of P. penguin at 3 different sites in northeastern Australia. By comparison, research interest in P. penguin, growth is increasing in China. For example, Liang et al. (2001a, 2001b) reported an 11-mo period of culture of hatchery-produced P. penguin to adult size in Liusha Bay, Zhanjiang, Guangdong Province; Gu et al. (2009) examined the growth of the winged pearl oyster P. penguin cultivated in Li'an Lagoon, Hainan Province, for a 20-mo period and established its growth model; and Fu et al. (2007) compared 2 different methods to culture midsize P. penguin (circle net and ear hanging) and reported the advantage of the latter over the former in both growth rate and survival rate. In general, the grow-out culture methods for P. penguin remain limited and mainly copy the techniques of Pinctada fucata martensii or Pinctada margaritafera by using nets or the ear-hanging method, but these methods involve high costs in either equipment or labor, and thus are far from perfect. The development of a novel method suitable for the growth characteristic of P. penguin is critical for the success of the industry.

The current study introduces a novel grow-out culture method of Pteria penguin using a specially designed wire collector that makes net change and cleaning unnecessary. The objective of this study was to examine the effectiveness of such a method by comparing the growth and survival of P. penguin cultured on the new collectors and in traditional circle nets in different stocking densities.

MATERIALS AND METHODS

Study Site and Biological Materials

The study was undertaken in Li'an Lagoon (latitude, 18[degrees]24-'18[degrees]26, N; longitude, 110[degrees] E), Hainan Island, South China. On March, 18, 2009, 20 female and male cultured Pteria penguin were induced to spawn using the protocols of Pinctada fucata martensii described in Gu et al. (2011). Fifteen days later, when larvae developed eye-spots and reached approximately 200 [micro]m, polyethylene rope-type collectors were deployed. Two months later, when spat had a mean shell length of 2.23 mm, the collectors together with spat were taken from the hatchery, placed into 1-mm mesh sleeves, and suspended from nursery rafts in Li'an Lagoon at a depth of 3 m at 30-cm intervals.

On August 7, 2009, at 142 days of age, juveniles were removed from the rope-type collectors and 3,200 oysters were chosen at random as samples. The growth parameters were measured as specified in Gu et al. (2009). The mean values of shell height (SH), maximum diagonal length (MDL), and hinge length (HL) of all oysters was 26.06 + 3.43 mm, 46.76 + 7.72 mm, and 49.36 + 9.58 mm, respectively, and total weight (TW) was 5.88 + 2.25 g; these values were obtained by measuring 1,000 oysters at random.

Different Methods of Cultivation

Thereafter, the samples were cultured differently. A total of 1,200 oysters were cultured in circle nets (diameter, 45 cm; net culture (NC) for short) in 3 stocking densities--10 juveniles (D10), 20 juveniles (D20), and 30 juveniles (D30) per net, each with 20 replicates. All nets were suspended from longlines at a depth of 3 m at 30-cm horizontal intervals and 1-m vertical intervals. The oysters were cleaned manually and the nets were changed once a month.

Two thousand oysters were cultured on specially designed wire collectors. The collector is made of galvanized seizing wire (diameter, 2.642 mm) and consists of 3 parts: a top circle (diameter, 20 cm), a bottom circle (diameter, 30 cm), and 3 30-cm-long pillars placed between the 2 circles (Fig. 1). The bottom circle is larger than the top circle so that the collectors can be piled together, and save space when put away.

Attachment of oysters to the collectors occurred as follows. First, the 2,000 oysters were placed into 4 250-[micro]m mesh sleeves, each containing around 500 spat. Then, every sleeve was placed within 1 wire collector (Fig. 1) and suspended from nursery rafts in Li'an Lagoon at a depth of 3m at 30-cm intervals. Three to five days later, the collectors were examined and the spat on it were counted. If a collector was settled with 150-200 juveniles, it was taken out of the mesh sleeve and suspended directly from the raft. Then, a new collector was put into the sleeve so that the remaining spat in the sleeve could settle. The whole process continued until all spat in a sleeve settled on the wire collectors. After that, the sleeves were removed and all spat were held on collectors and suspended in the sea. This manner of culture is called natural hanging (NH).

[FIGURE 1 OMITTED]

Measurement

From August 2009 to March 2010, measurement of the NC groups was conducted by collecting 100 oysters randomly from each group at monthly intervals. After cleaning them of fouling organisms, specimen were measured for SH, MDL, HL to the nearest 0.01 mm using digital vernier calipers, as described in Gu et al. (2009). Total weight, including shell and soft body, was weighed to the nearest 0.01 g with an electronic scale. In addition, survival rate was estimated by counting the remaining living oysters in all nets.

Measurement of the NH group differed a bit from that of the NC group. In this group, the oysters settled firmly on the wire with their byssi and had to be cut down for measurement, once they were cut down, they were unable to return to the original wire collectors and thus had to be removed, which made estimation of survival rate difficult. To solve the problem, the experimental group was further divided into 2 subgroups, each with 6 collectors and around 1,000 oysters. One subgroup was used to measure size and weight; the other was used to estimate survival rate. In first subgroup, every month, 100 oysters were cut down at random and measured; in the second group, the remaining oysters were counted and the morality rate was estimated. Oysters that dropped from the collectors into the sea were regarded as dead oysters.

Statistical Analysis

Size and weight data were compared using 1-way analysis of variance, with the means compared using Tukey's test from SPSS 18.0.

RESULTS

Growth of Different Groups

The mean values of size and weight of Pteria penguin at different times are shown in Table 1. From October 2009 to March 2010, most of the time, the largest oysters were recorded in the NH group. At the end of the experiment, the mean SH, MDL, and HL of the NH group was 91.29 [+ or -] 15.89 cm, 114.61 [+ or -] 16.53 cm, 130.67 [+ or -] 14.64 cm, and 130.67 [+ or -] 14.64, cm respectively; however, there was no significant difference (P > 0.05) between this group and the D10 group. The NH and D10 groups had significantly larger values in SH, MDL, and HL than the D20 and D30 groups. Oysters in the D30 group showed the lowest growth at the end of the experiment and were significantly smaller than in the D20 treatment.

The mean TW of pearl oysters at the end of the experiment varied considerably between groups (Table 1), to the extent that oysters in the NH group (mean TW, 122.13 [+ or -] 40.8 g) were more than 150% heavier than those from the D30 group (mean TW, 78.34 [+ or -] 24.69 g). Oysters of the NH treatment were heavier than those of the D10 groups for all measurements, but the differences were not significant (P > 0.05). The NH and D10 groups had significantly greater TW values than individuals in the D20 and D30 groups (P < 0.05). The D20 and D30 groups also had significantly different TW values.

Mortality Rate of Different Groups

Morality at the end of the experiment ranged from 3.3317.18 % (Table 1). The highest cumulative morality was found in the D30 (17.18%) and NH treatments (17%), whereas the lowest was recorded in the D10 treatment (3.33%), and the D20 group was in between (9.5%). From October 26, 2009, to the end of the experiment, the mortalities of the D30 and DH groups showed no significant differences, but both exhibited significant differences from those of the other 2 groups.

DISCUSSION

Oysters on the wire collectors had the largest gains in size and weight, suggesting an advantage of NH over high-density cage or NC in terms of growth. Methods of hanging oysters directly from longlines or rafts, without using cages or nets, have been adopted by a few species and generally attain a favorable growth rate, although they differ in specific techniques. For example, Beer (1999) used polyethylene ropes as a spat collector of Pteria penguin and suspended the collectors at 6 m from a longline. Fifteen months later, the spat on the collector ropes reached an SH of 100 mm, showing a greater grow rate than spat held within 3-mm mesh. In addition to the rope collector, another method is ear hanging. This method is used commonly in French Polynesia in the culture of Pinctada margaritafera by drilling a 2-3-mm hole through the base of the shell in the dorsal-posterior direction and tying the oyster to a "dropper rope" (called a chaplet), which is suspended from a raft or longline (Friedman & Southgate 1999). Southgate and Beer (2000) examined the growth rates of P. margaritafera held under 5 different culture techniques and observed a greater growth rate in ear hanging juveniles and juveniles in 24-pocket panel nets than those in other treatments. Similarly, Fu et al. (2007) reported that the growth rate of P. penguin using ear hanging was superior to oysters held in pearl nets. Therefore, it is quite safe to conclude that NH by using collectors and ear hanging are preferable to promote the growth of oysters because, without the enclosure of cage or net, oysters realize increased food availability and greater circulation of water (Southgate 2008).

Despite its beneficial effects on the growth of oysters, the NH group in the current study had a loss close to D30 (>17%), which was significantly greater than that of the D10 and D20 groups. The mortality of the NH treatment is most likely attributed to the predation of crabs. Without the protection of mesh, predation is a leading disadvantage of methods such as ear hanging or NH using collectors. Beer (1999) reported severe mortality of Pteria penguin caused by fish predation. Southgate and Beer (2000) reported that the mortality of Pinctada margaritafera juveniles by ear hanging (6.25%) was greater than that of oysters held in panel nets (0%) or plastic mesh trays (1.05%) during a 150-day experiment.

Selection of suitable culture methods must take biological, economic, and practical factors into account, such as growth and survival, cost of equipment, ease of construction, and frequency of cleaning (Southgate & Beer 2000). In the current study, the D10 treatment achieved both the highest growth and survival; however, this method involved the highest costs in terms of equipment and labor because low stocking density requires more nets and more manual labor for net changing and cleaning. If oysters were held at 20 per net, the cost of nets and labor for net changing would be reduced by half, but would result in either a prolonged time for oysters to reach an appropriate size for pearl production or more frequent shell cleaning because the greater density may cause poorer water circulation and more serious fouling. Claereboudt et al. (1994) estimated that as much as 30% of the operating costs of giant scallop farming are devoted to cleaning; however in Li'an, Hainan, because of the severe pollution of the water, this ratio rises to 70%, according to the local farmers.

In comparison, NH by using wire collectors is a relatively appropriate choice in Li'an Lagoon because this method can reduce dramatically the costs of equipment and labor, because it requires no net or net changing, and cleaning can be conducted using a pressure cleaner once every 3 months. Admittedly, NH mortality was greater than the treatments of D10 and D20, but the loss of oysters can be balanced positively by the growth rate and cost reduction, because the spat were hatchery produced and easily available.

The NH method used in this study has an advantage over ear hanging (Southgate & Beer 2000) and rope collectors (Beer 1999). Unlike ear hanging, the NH method allows oysters to attach to wires naturally through their powerful byssal threads, requiring no drilling of holes through shells or attaching oysters individually to dropper ropes, which is labor intensive and may cause considerable disturbance to oysters. As for the use of rope collectors (Beer 1999) in the spat culture of Pteria penguin, this is similar to the NH treatment used in this study, except for the differences in the material and shape of the collector. Beer (1999) used teased polyethylene ropes as collectors, and cultured the spat by hanging the spat collector ropes on longlines for 15 mo. This method has the advantage of convenient construction, because the rope collectors are easily obtainable; however, the number of spat on a rope collector should be strictly limited because, on the one hand, a rope has a relatively narrow space, and high density may lead to poor food availability and abnormal shell shapes; on the other hand, if too many juveniles settle on a rope, when spat grow bigger, they may exceed the strength of the rope and fall. Therefore, whether juveniles can remain on the rope collector until adulthood (ready for pearl production) is a question to be answered. By comparison, the collector in this study is spacious enough for attachment and tough enough to hold up to 150-200 10-cm MDL juveniles. Thereafter, when oysters grow larger than 10 cm MDL and become too heavy for the collector to carry, the collector is cut into several 30-cm wire threads attached with oysters, and the individual thread is suspended horizontally from longlines for further culture until pearl production.

ACKNOWLEDGMENTS

This study was funded by the National Program on Key Basic Research Program of China (973 Program, 2010CB126405), the National High Technology Research and Development Program of China (863 Program, 2012AA10A414), the National Science Foundation of China (41076112, 41366003), the National Science & Technology Pillar Program (2012BAC18B04), the International S&T Cooperation Program of China (2012DFG32200, 2013DFA31780), and the Project of Marine Development by Means of Science & Technology (XH 201314).

LITERATURE CITED

Beer, A. 1999. Larval culture, spat collection and juvenile growth of the winged pearl oyster, Pteria penguin. World Aquaculture'99. The annual International Conference and Exposition of the World Aquaculture Society 26th April-2nd May 1999, Sydney, Australia. Book of Abstracts, 63 pp.

Claereboudt, M. R., D. Bureau, J. Cote & J. H. Himmelman. 1994. Fouling development and its effect on the growth of juvenile giant scallops (Plaeopecten magellanicus) in suspended culture. Aquaculture 121:327-342.

Friedman, K. J. & P. C. Southgate. 1999. Grow-out of blacklip pearl oysters, Pinctada margaritafera (Linnaeus, 1758) on chaplets in suspended culture in Solomon Islands. J. Shellfish Res. 18:451-458.

Fu, S., C. Deng, F. Liang, H. Huang & R. Xie. 2007. Study on techniques of round-pearl and artificial cultivation in Pteria penguin (Roding). J. Guangdong Ocean Univ. 27:34-37. (In Chinese, with English abstract).

Gu, Z., Y. Shi, Y. Wang & A. Wang. 2011. Heritable characteristics in the pearl oyster Pinctada martensii: comparisons of growth and shell morphology of Chinese and Indian populations, and reciprocal crosses. J. Shellfish Res. 30:241-246.

Gu, Z., Q. Wang, J. Fang, Y. Shi, Y. Wang & A. Wang. 2009. Growth of cultured winged pearl oyster (Pteria penguin) in Li'an Lagoon, Hainan. Oceanol. Limnol. Sin. 40:423-429. (In Chinese, with English abstract).

Liang, F., S. Fu & X. Yu. 2001a. Study on the method of culture and spawning-inducing of Pteria penguin. Trans. Oceanol. Limnol.gy 2:41-45. (In Chinese, with English abstract).

Liang, F., Y. Mao & X. Yu. 2001b. A preliminary observation on the growth of the artificial spat of Pteria penguin. J. Zhanjiang Ocean Univ. 21:6-9. (In Chinese, with English abstract).

Milione, M. & P. C. Southgate. 2012. Growth of the winged pearl oyster, Pteria penguin, at dissimilar sites in northeastern Australia. J. Shellfish Res. 31:13-20.

Southgate, P. C. 2008. Pearl oyster culture. In: P. C. Southgate & J. S. Lucas, editors. The pearl oyster. Oxford: Elsevier. pp. 231-272.

Southgate, P. C. & A. C. Beer. 2000. Growth of blacklip pearl oyster (Pinctada margaritafera) juveniles using different nursery culture techniques. Aquaculture 187:97-104.

Zhang, L. 2007. Economical analysis of dilemma of Chinese pearl industry and outlet. Res. Agric. Modern. 28:403-407. (In Chinese, with English abstract).

GU ZHIFENG, WANG JUN, ZHAN XIN, SHI YAOHUA * AND WANG AIMIN *

Key Laboratory of Tropic Biological Resources of Ministry of Education, Hainan Key Laboratory of Tropical Hydrobiological Technology, The Ocean College, Hainan University, Haikou 570228

* Corresponding author. E-mail: stone70@126.com, aimwang@163.com

DOI: 10.2983/035.032.0307
TABLE 1.
Growth parameters of Pteria penguin cultured in different modes.

             Culture
Date          mode       n           SH (mm)

8/7/1909                1,000   26.06 [+ or -] 3.43
8/29/1909      NH       123    30.87 [+ or -] 3.08
               D10      105    30.59 [+ or -] 3.85
               D20      120    30.46 [+ or -] 3.52
               D30      119    30.17 [+ or -] 5.15
10/4/1909      NH       120    53.11 [+ or -] 4.3 (a)
               D10      104    52.93 [+ or -] 5.16 (a)
               D20      120    51.38 [+ or -] 7.11 (ab)
               D30      120    50.82 [+ or -] 6.89 (b)
10/26/1909     NH       120    57.32 [+ or -] 7.15 (a)
               D10      103    56.36 [+ or -] 6.06 (ab)
               D20      120    56.03 [+ or -] 7.25 (ab)
               D30      120    53.99 [+ or -] 6.99 (b)
12/2/1909      NH       80     65.21 [+ or -] 8.64 (a)
               D10      101    65.01 [+ or -] 7.08 (a)
               D20      101    61.77 [+ or -] 8.27 (b)
               D30      101    61.14 [+ or -] 9.37 (b)
12/29/1909     NH       80      72.3 [+ or -] 8.35 (a)
               D10      100    71.47 [+ or -] 8.24 (a)
               D20      100    67.79 [+ or -] 9.72 (b)
               D30      100    65.65 [+ or -] 10.17 (b)
1/28/1910      NH       80      75.7 [+ or -] 8.65 (a)
               D10      100     76.1 [+ or -] 9.81 (a)
               D20      100    73.68 [+ or -] 8.79 (a)
               D30      100    68.69 [+ or -] 9.3 (b)
3/10/1910      NH       78     91.29 [+ or -] 15.89 (a)
               D10      99     86.52 [+ or -] 12.45 (a)
               D20      99     80.38 [+ or -] 12.23 (b)
               D30      103    74.59 [+ or -] 9.6 (c)

Date              MDL (mm)                     HL (mm)

8/7/1909     46.76 [+ or -] 7.72         49.36 [+ or -] 9.58
8/29/1909    53.76 [+ or -] 6.09         62.97 [+ or -] 9.34
             52.45 [+ or -] 6.18         60.93 [+ or -] 8.38
             52.13 [+ or -] 6.17         56.66 [+ or -] 10.44
             51.32 [+ or -] 8.00         59.37 [+ or -] 10.42
10/4/1909    76.58 [+ or -] 6.32 (a)     92.12 [+ or -] 9.79 (a)
             75.33 [+ or -] 7.2 (a)      87.21 [+ or -] 13.16 (b)
             74.49 [+ or -] 8.7 (a)      83.47 [+ or -] 13.1 (b)
             74.02 [+ or -] 8.5 (a)      84.04 [+ or -] 13.63 (b)
10/26/1909   86.87 [+ or -] 10.63 (a)    97.85 [+ or -] 13.36 (a)
             85.13 [+ or -] 9.69 (a)     90.94 [+ or -] 10.45 (b)
              85.2 [+ or -] 11.38 (a)    89.71 [+ or -] 13.44 (b)
             79.49 [+ or -] 9.14 (b)     86.76 [+ or -] 10.59 (b)
12/2/1909    88.14 [+ or -] 5.23 (a)    107.42 [+ or -] 12.47 (a)
             87.38 [+ or -] 6.7 (a)     107.58 [+ or -] 11.91 (a)
             83.52 [+ or -] 10.15 (b)    98.55 [+ or -] 14.29 (b)
             83.45 [+ or -] 9.39 (b)     97.79 [+ or -] 13.49 (b)
12/29/1909   93.38 [+ or -] 8.08 (a)    108.06 [+ or -] 10.09 (a)
             92.29 [+ or -] 5.63 (a)    109.75 [+ or -] 10.58 (ab)
             88.65 [+ or -] 9.19 (b)    104.44 [+ or -] 11.15 (b)
             86.43 [+ or -] 7.68 (b)    100.31 [+ or -] 12.12 (c)
1/28/1910   102.17 [+ or -] 14.33 (a)   116.00 [+ or -] 14.94 (a)
             99.86 [+ or -] 11.77 (a)   114.26 [+ or -] 13.61 (a)
             95.68 [+ or -] 9.49  (b)   113.66 [+ or -] 12.16 (a)
             90.04 [+ or -] 6.01 (c)    105.63 [+ or -] 12.62 (b)
3/10/1910   114.61 [+ or -] 16.53 (a)   130.67 [+ or -] 14.64 (a)
            111.86 [+ or -] 14.47 (a)   127.85 [+ or -] 13.51 (a)
            103.95 [+ or -] 13.48 (b)   119.79 [+ or -] 14.46 (b)
              97.3 [+ or -] 9.5 (c)     112.96 [+ or -] 11.64 (c)

Date                 TW (g)             Mortality (%)

8/7/1909       5.88 [+ or -] 2.25
8/29/1909     16.11 [+ or -] 4.20         0
              10.90 [+ or -] 2.99         0.83
              10.80 [+ or -] 2.80         1.00
              10.35 [+ or -] 3.85         2.22
10/4/1909     31.93 [+ or -] 9.89 (a)     7.50 (a)
              30.99 [+ or -] 9.55 (ab)    0.83 (b)
              28.52 [+ or -] 10.22 (b)    1.50 (b)
              23.06 [+ or -] 8.06 (c)     3.33 (b)
10/26/1909     35.8 [+ or -] 12.28 (a)    9.50 (ab)
              32.68 [+ or -] 8.93 (ab)    1.67 (c)
              30.02 [+ or -] 9.91 (b)     5.50 (bc)
              26.37 [+ or -] 8.48 (c)    13.33 (a)
12/2/1909     54.67 [+ or -] 16.92 (a)   13.00 (a)
              51.87 [+ or -] 15.41 (a)    3.33 (b)
              43.99 [+ or -] 16.64 (b)    9.00 (b)
              43.36 [+ or -] 16.51 (b)   15.56 (a)
12/29/1909    71.68 [+ or -] 21.98 (a)   13.50 (ab)
               69.8 [+ or -] 17.42 (a)    3.33 (c)
              59.19 [+ or -] 21.73 (b)    9.00 (bc)
              53.85 [+ or -] 21.39 (b)   15.92 (a)
1/28/1910     83.97 [+ or -] 22.76 (a)   14.50 (ab)
              80.68 [+ or -] 22.46 (a)    3.33 (c)
              77.06 [+ or -] 19.04 (a)    9.50 (b)
              62.61 [+ or -] 22.13 (b)   17.41 (a)
3/10/1910    122.13 [+ or -] 40.81 (a)   17.00 (a)
             116.96 [+ or -] 34.07 (a)    3.33 (c)
              97.22 [+ or -] 31.63 (b)    9.50 (b)
              78.34 [+ or -] 24.69 (c)   17.78 (a)

D10, 10 oysters per net; D20, 20 oysters per net; D30, 30 oysters
per net; HL, hinge length; MDL, maximum diagonal length; NC, net
culture; NH, natural hanging on wire collectors; SH, shell
height; TW, total weight. All values represent mean [+ or -] SD. Mean
values with the same superscript are not significantly different
(Tukey's test, P < 0.05).
COPYRIGHT 2013 National Shellfisheries Association, Inc.
No portion of this article can be reproduced without the express written permission from the copyright holder.
Copyright 2013 Gale, Cengage Learning. All rights reserved.

Article Details
Printer friendly Cite/link Email Feedback
Author:Zhifeng, Gu; Jun, Wang; Xin, Zhan; Yaohua, Shi; Aimin, Wang
Publication:Journal of Shellfish Research
Article Type:Report
Geographic Code:9CHIN
Date:Dec 1, 2013
Words:4442
Previous Article:Broodstock conditioning, spawning induction, and early larval development of the tropical rock oyster Striostrea prismatica (Gray 1825).
Next Article:Growth and survival of pearl oyster Pinctada maxima spat reared under different environmental conditions.
Topics:

Terms of use | Copyright © 2017 Farlex, Inc. | Feedback | For webmasters