Printer Friendly

The effects of in breeding on production traits of the southern bay scallop Argopecten irradians concentricus.

ABSTRACT Argopecten irradians concentricus has been cultivated along the southern coast of China for about 16 generations since its first introduction in 1991. To determine the effects of self-fertilization on the production traits of this isolated bay scallop population, 12 self-fertilized families and a mass-spawned group were produced and studied. The hatching success and survival at larvae, juvenile, and adult stages of the offspring of the mass-mated group were all significantly greater than that of 10 of the 12 self-fertilized families examined, and not significantly different from that of other 2 self-fertilized families. For newly hatched larvae on day 1, no significant difference in size was found among the self-fertilized families and the mass-spawned group. The shell length of the mass-mated group on days 9, 30, 75 and 230, and the live weight on days 75 and 230 were always significantly larger than that of 9 of the 12 self-fertilized families, and not significantly different from that of the other 3 self-fertilized families. In addition, a significant difference in survival, shell length, and live weight was seen among the 12 self-fertilized families at all development stages. The current study demonstrated the occurrence of inbreeding depression for production traits in the closed population of A. irradians concentricus and the necessity of avoiding inbreeding when creating a breeding production, although not all families are significantly affected by inbreeding.

KEY WORDS: southern bay scallop, Argopecten irradians concentricus, self-fertilized families, production traits, inbreeding depression

INTRODUCTION

The bay scallop Argopecten irradians is a hermaphroditic marine bivalve native to the east coast of the United States. Two of its geographical subspecies, A. irradians irradians and A. irradians concentricus, were introduced to China as alternative species for aquaculture (Zhang et al. 1986, Zhang et al. 1997, Zheng et al. 2006). After being first introduced in 1991 (He & Zhang 1998), culture of the southern bay scallop A. irradians concentricus was quickly extended, because of the short growth period, low production costs, and high economic return. Now scallop culture is gaining momentum and has become one of the pillar industries in Beibu Bay in the South China Sea (Liu et al. 2007a). With the rapid development of bay scallop aquaculture, however, some problems such as high mortality, slow growth, and diseases appeared (Liu et al. 2007b). Zhang et al. (2000) suggested that genetic degradation as a result of inbreeding was one of the main problems facing the bay scallop aquaculture industry.

For small and isolated populations, genetic drift or mating between relatives may increase homozygosity, and then results in a reduction of the mean phenotypic value of traits associated with fitness, such as inbreeding depression (Charlesworth & Charlesworth 1987, Falconer & Mackay 1996). Genetic study with simple sequence repeat markers has demonstrated that the average heterozygosity and allelic diversity in cultured populations of bay scallop from China were lower than that of the wild populations from the east coast of America (Wang et al. 2007). All finite populations experience some degree of inbreeding (Falconer & Mackay 1996, Pante et al. 2001). Moreover, the bay scallop is a simultaneous hermaphrodite that releases successively male and female gametes during the spawning process. Like other functional hermaphrodites, self-fertilization is a common occurrence during spawning, which can result in inbreeding (Zheng et al. 2006). Mass spawning is used by farmers to produce scallop seeds, and the use of limited parents increases the chances of inbreeding.

Inbreeding reduces heterozygosity, limits the potential response to selection in subsequent generations, and increases the potential for inbreeding depression (Bentsen & Olesen 2002). Inbreeding depression has been documented during long-term breeding in aquatic animals (Jarne & Charlesworth 1993, De Donato et al. 2005, Neira et al. 2006). However, information on the effect of inbreeding in marine bivalve molluscs is limited and conflicting. In the American oyster Crassostrea virginica, for example, poor larval survivorship and growth were found in inbred groups (Longwell & Stiles 1973). For the same species and for the same inbreeding coefficient, no inbreeding effects were detected on larval growth or survival, although there was a 6-10% inbreeding depression on spat growth (Mallet & Haley 1983). With respect to the Pacific oyster, Crassostrea gigas, Beattie et al. (1987) found that inbreeding can reduce growth of 2-y-old individuals, but Lannan (1980) did not find effects of inbreeding on survival to spat. In the hermaphroditic scallop Argopecten purpuratus, no differences in survival or growth were found between families produced by self-fertilization and pair mating at either the larval or juvenile stages (Winkler & Estevez 2003). Ibarra et al. (1995) found lower growth rate and survivorship in larvae of the scallop Argopecten circularis produced by self-fertilization than that produced by outbreeding. In the tropical scallop Euvola ziczac, no effects of self-fertilization were detected on growth or survivorship (Betancourt et al. 1994). Therefore, not all inbred populations experience inbreeding depression (Falconer & Mackay 1996, Beattie et al. 1987). The magnitude of inbreeding depression may vary considerably depending on the species and the traits examined (Bentsen & Olesen 2002, Bondari & Dunham 1987), and it is imperative to assess the effects of inbreeding on production traits of any species targeted for breeding.

The current study was designed to determine the effects of inbreeding on production traits of a population of the southern bay scallop A. irradians concentricus cultured in China. A better understanding of this information will benefit the design of selective breeding programs for southern bay scallops.

MATERIALS AND METHODS

Broodstock

Parental scallops used in this study were descendants from the initial introduction from Florida in 1991, which has been successively cultured in Beibu Bay, South China Sea, for 16 y (about 16 generations). In December 2007, adult scallops were transported to a scallop seed hatchery in Zhanjiang and conditioned in a 20-[m.sup.3] concrete tank. The broodstock were fed with Isochrysis zhanjiangensis and Platymonas subcordiformis. Water was changed 30-50% every day, and the water temperature was maintained at 23[degrees]C until the breeders reached ripeness (stage IV).

Experimental Design and Treatments

Two groups, one using self-fertilization and the other using mass mating, were produced. Scallops with turgid, well-colored gonads were chosen as parents and induced to spawn using temperature and UV radiation shock. For the self-fertilized group, 12 individuals randomly selected from the adult parents were placed individually in an 80-L bucket and allowed to spawn to produce self-fertilized larvae. Thus, 12 self-fertilized families were produced using sperm and eggs from the same individuals. Fertilized eggs of each self-fertilized family were separated into 3 replicates, and then each replicate was placed in 1 200-L concrete tank. For the mass-spawned group, 50 individuals randomly selected from the adult parents were placed in a 10,000-L concrete tank and allowed to mass spawn. Partial self-fertilized eggs randomly selected from the 10,000-L concrete tank were separated into 3 replicates, and each replicate was placed in a 200-L concrete tank.

At about 30 h after fertilization, larvae from each of the 39 replicates were collected using a 20-[micro]m-mesh sieve and placed in a 10-L bucket with seawater. Numbers of larvae in each tank were estimated by counting in triplicate the number of larvae in 1 mL and extrapolating to the total holding volume. Then, D-stage larvae from each replicate were placed in a 200-L concrete tank. Initial density for all replicates in the experiment was set at 4 larvae/mL.

To minimize environmental effects, rearing conditions were maintained the same for all replicates at the larval, juvenile, and adult stages. The larvae were fed with k zhanjiangensis from days 2-6, and then with a mixture of I. zhanjiangensis and P. subcordiformis (1:1), with concentrations ranging from 15,000-50,000 cells/mL according to larvae aging. With larval growth, densities were kept the same by adjusting the water volume. Seawater used was sand filtrated and sterilized by UV radiation. Water was changed 30-50% every day. Water temperature was left to change with the outside environment, and salinity was kept at 28.9-29.8. After 9 days of larval culture, when about 30% of larvae developed to the eye stage in some replicates, spat collectors (polyethylene nets) were placed into the tanks. Metamorphosed and attached spat were kept in the concrete tanks until they reached 1 mm (on day 30), then they were placed in polyethylene bags and transferred to an outdoor nursery area in the sea. In the spat nursery, polyethylene bags were changed as spat aged; spat was sorted once every month to reduce density.

Three months later, all juveniles were transferred to 10-layer cages for grow-out. Densities were adjusted monthly, starting with 200 individuals per layer and ending with 30 individuals per layer.

Sampling, Measurement, and Inbreeding Depression Estimates For each replicate, the hatching success and survival at the larval, juvenile, and adult stages were estimated. The shell length and live weight were measured for juveniles and adults.

Hatching success was estimated as the ratio of the number of normal D-stage larvae to the number of fertilized eggs. Survival at the larval stage was estimated as the ratio of the number of surviving larvae on day 9 versus the number of D-stage larvae on day 1. Survival at the juvenile and adult stages was estimated as the ratio of the number of surviving juveniles on day 75 versus the number of juveniles on day 30, and the ratio of the number of surviving adults on day 230 versus the number of juveniles on day 75. For larvae/spat on day 1, 9 and 30, shell size of 40 individuals randomly sampled from each replicate was measured using a microscope (100x) equipped with an ocular micrometer. At the juvenile and adult stages, a random subsample of 30 scallops from each replicate was measured for shell size using a vernier caliper (0.02-mm accuracy) on days 75 and 230, respectively. Live weight of 30 individuals randomly sampled from each replicate for juveniles on day 75 and adults on day 230 was measured individually using an electronic balance.

The magnitude of inbreeding depression ([delta]) is calculated as the proportional decrement in the mean phenotypic value caused by self-fertilization in comparison with mass-mated offspring (Charlesworth & Charlesworth 1990, Crnokrak & Roff 1999):

[delta] = 1 - [W.sub.1]/[W.sub.0]

where, [W.sub.1] is the phenotypic value of self-fertilized offspring and [W.sub.0] is the phenotypic value of mass-mated offspring.

Statistical Analysis

One-way analysis of variance was carried out to determine the differences in production traits. When there were significance differences, the means were further compared with Duncan's multiple range tests. Analyses were done using Statistical Program for Social Sciences (SPSS 12.0, Chicago, IL) software for Windows. Significance level for all analyses was set at P < 0.05.

RESULTS

Hatching and Survivorship

The observed hatching rates and survivorship at the larval, juvenile, and adult stages for the mass-spawned group (CG) and the 12 self-fertilized families (SF1-SF12) in the self-fertilized group are shown in Table 1. The hatching rate of CG (54.85%) was significantly larger than that of the self-fertilized group for 10 of the 12 self-fertilized families examined, and not significantly different from that of the other 2 self-fertilized families (SF2 and SF9). Hatching success varied from 22.73-56.67% among the 12 self-fertilized families (SF1-SF12), with an average of 35.84%. During the larval, juvenile, and adult stages, the survival of the mass-mated group was 53.54%, 77.93%, and 85.93%, respectively, which was always significantly higher than that of self-fertilized families at corresponding stages, except for SF2 and SF9. In addition, a significant difference in survival was found among the 12 self-fertilized families at all developmental stages.

The magnitude of inbreeding depression ([delta]) for traits in hatching and survivorship is shown in Table 2. The estimated inbreeding depression for hatching varied from 21.17-63.87%, with an average of 40.45%. The estimated mean value of inbreeding depression for survival at the larval, juvenile, and adult stages was 41.80%, 24.29%, and 18.71%, respectively.

Growth

Shell length and/or live weight at different ages for the 12 families (SF1-SF12) of the self-fertilized group and the mass-spawned group (CG) of the southern bay scallop are listed in Table 3. For newly hatched larvae on day 1, no significant difference in size was found between the self-fertilized families and the mass-spawned group. From day 9 to day 230, however, the shell length and live weight were significantly affected by the mating system (self-fertilization vs. mass mating). The shell length of the mass-mated group on days 9, 30, 75, and 230, and the live weight on days 75 and 230 were always significantly larger than that of the self-fertilized group for 9 of the 12 self-fertilized families examined, and not significantly different from that of the other 3 self-fertilized families (SF2, SF3, and SF9). In addition, a significant difference in shell length on days 9, 30, 75, and 230, and in live weight on days 75 and 230 was detected among the 12 self-fertilized families.

The magnitude of inbreeding depression (8) in shell length and live weight at different ages is presented in Table 4. The average inbreeding depression for shell length on days 9, 30, 75, and 230 was 10.36%, 25.90%, 21.08%, and 20.94%, respectively. The inbreeding depression for wet weight on days 75 and 230 was 42.21% and 32.85%, respectively.

DISCUSSION

Inbreeding is unavoidable in closed populations (Falconer & Mackay 1996, Pante et al. 2001). Unless managed strategically, inbreeding itself is almost universally harmful, and breeders normally seek to avoid levels that produce inbreeding depression (Falconer & Mackay 1996). Understanding the effects of inbreeding is critical to the long-term viability of shellfish breeding programs, especially as breeders attempt to develop selected lines in hatcheries with small, effective population sizes. For 10 of the 12 self-fertilized families of southern bay scallop A. irradians concentricus examined in the current study, inbreeding depression for production traits, hatching, survival, and growth was evident. Similar results have also been reported on A. irradians irradians, the northern subspecies of bay scallop (Stiles & Choromanski 1995, Zheng et al. 2008). These results were consistent with previous studies on 2 other hermaphroditic scallops: Pecten maximus (Beaumont & Budd 1983, Beaumont 1986) and A. circularis (Ibarra et al. 1995). In contrast, however, no evidence of inbreeding depression was found in either larvae or juveniles of 2 tropical hermaphroditic scallops: E. ziczac (Betancourt et al. 1994) and A. purpuratus (Winkler & Estevez 2003).

For simultaneous hermaphrodites, inbreeding depression is regarded as the most important selective force acting against self-fertilization, and maintaining cross-fertilization (Lande & Schemske 1985, Charlesworth & Charlesworth 1987). Several theoretical analyses predict that inbreeding depression under self-fertilization should be greater than 0.5 to maintain cross-fertilization (Maynard Smith 1978, Charlesworth & Charlesworth 1990). The levels of inbreeding depression for production traits we report here (Tables 2 and 4) were low compared with those found in previous studies in some simultaneous hermaphrodites (Jarne & Delay 1990, Chen 1993, Li & Pechenik 2007). One possible reason for this discord is the special breeding and mating history of the closed population of A. irradians concentricus studied here. After its introduction to the southern coast of China, the southern bay scallop has been successively cultured for nearly 2 decades (about 16 generations). All finite populations experience some degree of inbreeding (Pante et al. 2001, Falconer & Mackay 1996). Like other functional hermaphrodites, self-fertilization is a common occurrence during spawning, which can also result in some amount of inbreeding (Zheng et al. 2006). Mass spawning is used by farmers to produce scallop seed, and the use of limited parents in mating situations increases the chance of inbreeding. Theoretical genetic models showed that small amounts of "selfing" could reduce inbreeding depression (Lande & Schernske 1985, Charlesworth & Charlesworth 1990). High inbreeding depression is expected in cross-fertilizing species and relatively low inbreeding depression in self-fertilizing species (Maynard Smith 1978, Wells 1979, Lande & Schernske 1985, Charlesworth & Charlesworth 1987). Therefore, the normal occurrence of self-fertilization can explain the decline in the magnitude of inbreeding depression in the bay scallop population examined here. The magnitude of inbreeding depression detected in the current study is similar to that from a population of A. irradians irradians, which was introduced to the northern coast of China several decades ago (Zheng et al. 2008). In addition, the bay scallop is a simultaneous hermaphrodite; thus, partial self-fertilization was inevitable during mass spawning. The control group we used in the current study may exhibit an unknown amount of self-fertilization and may not be representative of a strict outcross population, which can also lead to an underestimation of inbreeding depression.

It is clear that the effects of inbreeding varied among families. For example, the offspring of 2 self-fertilized families, SF2 and SF9, did not show any effects of inbreeding for the traits that exhibited inbreeding depression in other families. The variety of responses and the range of variation in this study indicate that not all families were adversely affected by inbreeding. According to the partial dominance hypothesis, inbreeding depression results from the phenotypic expression of deleterious recessive or partially recessive alleles that are at least partially masked in the heterozygous condition. Inbreeding increases the proportion of individuals that are homozygous for such recessive alleles, allowing their full expression (Charlesworth & Charlesworth 1987, Crnokrak & Barrett 2002). Different families can harbor different proportions of deleterious alleles (mutation load) simply through random genetic drift (Frankham et al. 2002). It is possible that families SF2 and SF9 carried a lighter mutation load than other families and therefore suffered the least from inbreeding. In addition, some uncontrolled biological effects inherent in bay scallop may lead to the variety of responses. Different effects of inbreeding for different families have also been found in several marine invertebrates (Keys et al. 2004, Park et al. 2006, Li & Pechenik 2007). Results of the current study also indicate that inbreeding and heterosis may be exploited for strain development in the southern bay scallop A. irradians concentricus in the future.

ACKNOWLEDGMENTS

This research is supported by Agricultural Science and Technology transfer funds of the Ministry of Science and Technology of China (2007GB2E000183), the Science and Technology Program of Guandong Province of China (2006B20201055), and the Program of Department of Education of Guangdong Province of China (2009B090300232). We also appreciate the helpful comments of the anonymous referees, which improved the manuscript.

LITERATURE CITED

Beattie, J. H., J. Perdue, W. Hershberger & K. Chew. 1987. Effect of inbreeding on growth in the Pacific oyster Crassostrea gigas. J. Shellfish Res. 6:25-28.

Beaumont, A. R. 1986. Genetic aspects of hatchery rearing of the scallop, Pecten maximus (L.). Aquaculture 57:99-110.

Beaumont, A. R. & M. D. Budd. 1983. Effects of self-fertilisation and other factors on the early development of the scallop Pecten maximus. Mar. Biol. 76:285-289.

Bentsen, H. B. & I. Olesen. 2002. Designing aquaculture mass selection programs to avoid high inbreeding rates. Aquaculture 204: 349-359.

Betancourt, R. J., J. E. Perez, J. E. Velez, L. Freites & M. I. Segnini. 1994. Efectos de la consanguinidad en la vieira Euvola ziczac. Bol. Inst. Oceanogr. Venez. Univ. Oriente 34:69-75.

Bondari, K. & R. A. Dunham. 1987. Effects of inbreeding on economic traits of channel catfish. Theor. Appl. Genet. 74:1-9.

Charlesworth, D. & R. A. Charlesworth. 1987. Inbreeding depression and its evolutionary consequences. Annu. Rev. Ecol. 18:237-268.

Charlesworth, D. & B. Charlesworth. 1990. Inbreeding depression with heterozygote advantage and its effect on selection for modifiers changing the outcrossing rate. Evolution 44:870-888.

Chen, X. 1993. Comparison of inbreeding and outbreeding in hermaph-roditic Arianta arbustorum (L.) (land snail). Heredity 71:456-461.

Crnokrak, P. & S. C. H. Barrett. 2002. Perspective: purging the genetic load: a review of the experimental evidence. Evolution 56:2347-2358.

Crnokrak, P. & D. A. Roff. 1999. Inbreeding depression in the wild. Heredity 83:260-270.

De Donato, M., R. Manrique, R. Ramirez, L. Mayer & C. Howell. 2005. Mass selection and inbreeding effects on a cultivated strain of Penaeus (Litopenaeus) vannamei in Venezuela. Aquaculture 247: 159-167.

Falconer, D. S. & T. F. C. Mackay. 1996. introduction to quantitative genetics, 4th ed. Essex, UK: Longman. 464 pp.

Frankham, R., J. D. Ballou & D. A. Briscoe. 2002. Introduction to conservation genetics. Cambridge: Cambridge University Press. 617 pp.

He, Y. C. & F. S. Zhang. 1998. Effect of salinity on embryo and larval development of the southern bay scallop Argopecten irradians concentricus Say. Chin. J. Oceanol. Limnol. 16:91-96.

Ibarra, A. M., P. Cruz & B. A. Romero. 1995. Effects of inbreeding on growth and survival of self-fertilized Catarina scallop larvae, Argopecten circularis. Aquaculture 134:37-47.

Jarne, P. & D. Charlesworth. 1993. The evolution of the selfing rate in functionally hermaphrodite plants and animals. Annu. Rev. Ecol. 24: 441-466.

Jarne, P. & B. Delay. 1990. Inbreeding depression and sell-fertilization in Lymnaea peregra (Gastropoda: Pulmonata). Heredity 64:169-175. Keys, S. J., P. J. Crocos, C. Y. Burridge, G. J. Coman, G. P. Davis & N. P. Preston. 2004. Comparative growth and survival of inbred and outbred Penaeus (marsupenaeus) japonicus, reared under controlled environment conditions: indications of inbreeding depression. Aquaculture 241 : 151-168.

Lande, R. & D. W. Schemske. 1985. The evolution of self-fertilization and inbreeding depression in plants. I. Genetic models. Evolution 39: 24-40.

Lannan, J. E. 1980. Broodstock management of Crassostrea gigas. 1. Genetic and environmental variation in survival in the larval rearing system. Aquaculture 21:323-336.

El, W. & J. A. Pechenik. 2007. Effect of inbreeding on reproduction and juvenile performance in two marine gastropods with contrasting reproductive patterns. Mar. Ecol. PR. 346:219-234.

Liu, Z. G., H. Wang & S. W. Fu. 2007a. Morphological growth of cultured Argopecten irradians concentricus Say in Beibu Bay in Zhanjiang. J. Fish. China 31:675-681.

Liu, Z. G., H. Wang & Y. L. Zheng. 2007b. The effect of parental selection on inbred first filial generation of Argopecten irradians concentricus Say. J. Fish. China 31:443-451.

Longwell, A. C. & S. S. Stiles. 1973. Gamete cross incompatibility and inbreeding in the commercial American oyster, Crassostrea virginica Gmelin. Cytologia (Tokyo) 38:521.

Mallet, A. L. & L. E. Haley. 1983. Effects of inbreeding on larval and spat performance in the American oyster. Aquaculture 38:521-533.

Maynard Smith, J. 1978. The evolution of sex. Cambridge: Cambridge University Press. 222 pp.

Neira, R., N. F. Diaz, G. A. E. Gall, J. A. Gallardo, J. P. Lhorente & R. Manterola. 2006. Genetic improvement in Coho salmon (Oncorhynchus kisutch), I: selection response and inbreeding depression on harvest weight. Aquaculture 257:9-17.

Pante, M. J. R., B. Gjerde & I. Mcmillan. 2001. Inbreeding levels in selected populations of rainbow trout, Oncorhynchus mykiss. Aquaculture 192:213-224.

Park, C., Q. Li, T. Kobayashi & A. Kijima. 2006. Inbreeding depression traits in Pacific abalone Haliotis discus hannai by factorial mating experiments. Fish. Sci. 72:774-780.

Stiles, S. & J. Choromanski. 1995. Inbreeding studies on the bay scallop, Argopecten irradians. J. Shellfish Res. 14:278.

Wang, L., H. Zhang, L. Song & X. Guo. 2007. Loss of allele diversity in introduced populations of the hermaphroditic bay scallop Argopecten irradians. Aquaculture 271:252-259.

Wells, H. 1979. Self-fertilization: advantageous or deleterious'? Evolution 33:252-255.

Winkler, F. M. & B. F. Estevez. 2003. Effects of self-fertilization on growth and survival of larvae and juveniles of the scallop Argopecten purpuratus L. J. Exp. Mar. Biol. Ecol. 292:93-102.

Zhang, F., H. Ch & Y. Sh. 2000. Introduction engineering of bay scallop and its comprehensive effects. Eng. Sci. 2:30-35.

Zhang, F., Y. He, X. Liu, J. Ma, S. Li & L. Qi. 1986. A report on the introduction, spat-rearing and experimental culture of bay scallop, Argopecten irradians Lamarck. Oceanol. Limnol. Sin. 17:367-374.

Zhang, F., Y. He, L. Qi & L. Sun. 1997. Studies on the restoration of cultured bay scallop Argopecten irradians through reintroduction of broodstock. Oceanol. Limnol. Sin. 28:151-163.

Zheng, H., G. Zhang, X. Guo & X. Liu. 2008. Inbreeding depression for various traits in two cultured populations of the American bay scallop, Argopecten irradians irradians Lamarck (1819) introduced into China. J. Exp. Mar. Biol. Ecol, 364:42-47.

Zheng, H., G. Zhang, X. Liu & X. Guo. 2006. Sustained response to selection in an introduced population of the hermaphroditic bay scallop Argopecten irradians irradians Lamarck (1819). Aquaculture 255:579-585.

JIANYONG LIU, (1) ZHIGANG LIU (1),* AND XIAOZHEN SUN (2)

(1) Fisheries College, Guangdong Ocean University, 40 Jiefangdong Road, Zhanjiang, Guangdong 524025, China," (2) Zhanjiang Silver Wave Pearl Company, 40 Jiefangdong Road, Zhanjiang, Guangdong 524000, China

* Corresponding author. E-mail: lzg919@2lcn.com

DOI: 10.2983/03.030.011
TABLE 1.
Hatching rate and survival at the larval, juvenile, and adult
stages for the 12 families (SF1-SF12) and the mass-spawned
group (CG) of the southern bay scallop A. irradians
concentricus.

                                       Survival (%)
            Hatching
Group       Rate (%)             Larva             Juvenile

SF1     43.21 (b) (1.22)   37.63 (b) (3.10)    65.78 (bc) (5.24)
SF2     56.42 (a) (1.88)   53.64 (a) (3.20)    81.47 (a) (3.20)
SF3     19.82 (d) (0.55)   31.98 (cd) (2.33)   44.21 (d) (5.59)
SF4     22.87 (c) (1.33)   29.22 (d) (3.43)    59.44 (c) (3.57)
SF5     42.83 (b) (1.24)   32.96 (bc) (2.17)   69.91 (b) (4.17)
SF6     43.63 (b) (1.39)   36.83 (bc) (4.04)   64.85 (bc) (5.34)
SF7     42.83 (b) (1.56)   34.02 (bc) (2.21)   66.02 (b) (4.04)
SF8     23.36 (c) (1.34)   24.34 (d) (2.34)    50.65 (d) (3.33)
SF9     56.67 (a) (1.69)   55.84 (a) (4.24)    78.87 (a) (4.25)
SF10    23.14 (c) (1.11)   27.56 (d) (2.87)    61.11 (c) (3.63)
SF11    42.23 (b) (1.52)   28.18 (d) (4.55)    58.18 (c) (3.33)
SF12    22.73 (c) (1.23)   28.87 (d) (3.27)    49.87 (d) (5.25)
CG      54.85 (a) (1.56)   53.54 (a) (2.66)    77.93 (a) (2.58)

          Survival (%)

Group         Adult

SF1     77.67 (b) (2.22)
SF2     86.48 (a) (3.90)
SF3     63.09 (d) (4.58)
SF4     66.09 (cd) (4.45)
SF5     73.96 (bc) (3.37)
SF6     70.53 (c) (3.32)
SF7     79.02 (b) (2.66)
SF8     67.65 (cd) (3.33)
SF9     86.65 (a) (2.25)
SF10    71.09 (c) (3.13)
SF11    68.54 (cd) (5.01)
SF12    60.85 (d) (4.22)
CG      85.93 (a) (3.87)

SDs are in parentheses. Within each column, means with the same
superscripts are not statistically different (P > 0.05).

TABLE 2.
Inbreeding depression ([delta]) for hatching success and survival at
the larval, juvenile, and adult stages of the southern bay scallop
A. ivradians concentricus.

                                Survival (%)
          Hatching Rate
Group          (%)        Larva   Juvenile   Adult

SF1           21.17       29.72    15.59      9.61
SF3           63.87       40.27    43.27     26.58
SF4           58.39       45.42    23.73     23.09
SF5           21.90       38.44    10.29     13.93
SF6           20.44       31.21    16.78     17.92
SF7           21.90       36.46    15.28      8.04
SF8           57.48       54.54    35.01     21.27
SF10          57.85       48.52    21.58     17.27
SF11          22.99       47.37    25.34     20.24
SF12          58.58       46.08    36.01     29.19
Average       40.45       41.80    24.29     18.71

As the hatching rate and survival of SF2 and SF9 were not
significantly different from that of the CG, the inbreeding
depression values of SF2 and SF9 were not listed.

TABLE 3.
Shell length (SL) and live weight (W) at different ages of the
southern bay scallop A. irradians concentricus.

            Day 1             Day 9               Day 30
Group   SL ([micro]m)     SL ([micro]m)          SL (mm)

SF1     95.81 (2.14)    155.94 (cd) (3.26)   0.99 (bc) (0.08)
SF2     97.62 (2.12)    169.78 (ab) (3.27)   1.23 (a) (0.11)
SF3     96.42 (1.94)    175.50 (a) (3.23)    1.21 (ab) (0.10)
SF4     96.47 (1.83)    154.06 (d) (4.27)    0.88 (c) (0.10)
SF5     96.22 (2.14)    162.58 (bc) (4.26)   1.05 (b) (0.09)
SF6     96.28 (2.15)    163.49 (b) (4.28)    0.95 (bc) (0.09)
SF7     96.63 (2.21)    166.82 (b) (3.24)    1.04 (b) (0.08)
SF8     95.43 (1.94)    149.85 (d) (2.32)    0.87 (c) (0.11)
SF9     96.42 (1.21)    172.91 (a) (3.34)    1.21 (ab) (0.09)
SF10    95.48 (2.73)    155.27 (c) (4.41)    0.86 (c) (0.07)
SF11    96.62 (2.12)    157.36 (c) (4.22)    0.97 (bc) (0.07)
SF12    95.2 (1.15)     149.14 (d) (4.32)    0.86 (b) (0.07)
CG      97.52 (2.12)    175.34 (a) (4.24)    1.27 (a) (0.08)

                        Day 75

Group        SL (mm)             W (g)

SF1     18.34 (bc) (1.24)   1.59 (c) (0.24)
SF2     20.42 (a) (1.20)    2.05 (ab) (0.20)
SF3     20.14 (ab) (2.52)   2.22 (a) (0.22)
SF4     14.66 (d) (2.07)    0.88 (d) (0.34)
SF5     18.10 (bc) (1.17)   1.69 (bc) (0.17)
SF6     18.16 (bc) (1.32)   1.69 (bc) (0.21)
SF7     17.40 (bc) (2.06)   1.58 (c) (0.28)
SF8     14.58 (d) (1.39)    0.80 (d) (0.39)
SF9     20.21 (ab) (1.28)   1.94 (ab) (0.23)
SF10    15.74 (cd) (1.64)   0.79 (d) (0.33)
SF11    18.58 (bc) (1.33)   1.62 (b) (0.31)
SF12    16.66 (cd) (2.23)   0.75 (d) (0.20)
CG      21.43 (a) (1.32)    2.19 (a) (0.28)

                        Day 230

Group       SL (mm)             W (g)

SF1     40.96 (b) (2.12)   20.44 (b) (1.12)
SF2     50.14 (a) (2.44)   27.24 (a) (1.33)
SF3     51.64 (a)(2.49)    27.42 (a) (1.37)
SF4     35.56 (c) (2.32)   14.24 (c) (1.21)
SF5     40.62 (b) (2.10)   21.36 (b) (1.23)
SF6     40.58 (b) (2.24)   21.42 (b) (1.24)
SF7     40.24 (b) (2.23)   20.87 (b) (1.22)
SF8     34.68 (c) (2.15)   14.22 (c) (1.28)
SF9     51.68 (a) (2.20)   27.65 (a) (1.27)
SF10    35.78 (c) (2.32)   14.92 (c) (1.14)
SF11    41.86 (b) (2.40)   20.89 (b) (1.16)
SF12    34.38 (c) (2.26)   14.32 (c) (1.21)
CG      48.44 (a) (2.55)   26.92 (a) (1.45)

SDs are in parentheses. Within each column, means with the same
superscripts are not statistically different (P > 0.05).

TABLE 4.
Inbreeding depression ([delta]) in shell length (SL) and live weight
(W) of the southern bay scallop A. irradians concentricus at
different ages.

                                          Day 75          Day 230
              Day 9       Day 30
Group     SL ([micro]m)   SL (mm)   SL (mm)   W (g)   SL (mm)   W (g)

SF1           11.06        22.05     14.42    27.40    15.44    24.07
SF4           12.14        30.71     31.59    59.82    26.59    47.10
SF5            7.28        17.32     15.54    22.83    16.14    20.65
SF6            6.76        25.20     15.26    22.83    16.23    20.43
SF7            4.86        18.11     18.81    27.85    16.93    22.47
SF8           14.54        31.50     31.96    63.47    28.41    47.18
SF10          11.45        32.28     26.55    63.93    26.14    44.58
SF11          10.25        23.62     13.30    26.03    13.58    22.40
SF12          14.94        32.28     22.26    65.75    29.03    46.81
Average       10.36        25.90     21.08    42.21    20.94    32.85

As the shell length and live weight of SF2, SF3, and SF9 were not
significantly different from that of CG, the inbreeding depression
values of SF2, SF3 and SF9 were not listed.
COPYRIGHT 2011 National Shellfisheries Association, Inc.
No portion of this article can be reproduced without the express written permission from the copyright holder.
Copyright 2011 Gale, Cengage Learning. All rights reserved.

Article Details
Printer friendly Cite/link Email Feedback
Author:Liu, Jianyong; Liu, Zhigang; Sun, Xiaozhen
Publication:Journal of Shellfish Research
Article Type:Report
Geographic Code:9CHIN
Date:Apr 1, 2011
Words:5292
Previous Article:The effects of egg stocking density and antibiotic treatment on survival and development of winged pearl oyster (Pteria penguin, Roding 1798) embryos.
Next Article:The fate of Spondylus stocks (Bivalvia: Spondylidae) in Ecuador: is recovery likely?
Topics:

Terms of use | Privacy policy | Copyright © 2022 Farlex, Inc. | Feedback | For webmasters |