**1. Introduction**

108 Aquaculture

Tatsadjieu Ngouné L., Maiworé J., Hadjia B.M., Loiseau G., Montet D., Mbofung C.M., 2010.

Van Hannen, E.J., Zwart, G., van Agterveld, M.P., Gons, H.J., Ebert, J., Laanbroek, H.J., 1999.

Yang, C.H., Crowley, D.E., Menge, J.A., 2001. 16S rDNA fingerprinting of rhizosphere

control 21, 673-678.

roots. FEMS Microbiol. Ecol. 35, 129-136.

65, 795-801.

Study of the microbial diversity of *Oreochromis niloticus* of three lakes of Cameroon by PCR-DGGE: Application to the determination of the geographical origin. Food

Changes in bacterial and eukaryotic community structure after mass lysis of filamentous cyanobacteria associated with viruses. Appl. and Environ. Microbiol.

bacterial communities associated with healthy and Phytophthora infected avocado

The determination and the identification of species constitute some of the first basic steps for biodiversity monitoring and conservation (Dayrat, 2005). Species identification is usually carried out by taxonomists, but in many cases it is restricted by the lack of available morphological characters. This is the case for two *Flexopecten* taxa: *Flexopecten glaber* L. and *F. proteus* Dillwyn ex Solander ms. The smooth scallop *F. glaber* is an edible bivalve, with a maximum length of 8.66 cm (Pisor & Poppe, 2008). It is an epibenthic species of soft and/or hard substrate and its habitat is characterized as muddy and sandy, with organic detritus. The species has a fast growth rate. Its reproduction takes place mainly during late summer, while the gonad activity can be observed all the year. It inhabits between 5 and 900 m depth or more (even 1600 m), in Mediterranean and Black Seas (Poppe & Goto, 1993) and its distribution appears in Figure 1.

The expansion of *F. proteus* is controversial, since some authors reported restricted distribution of the species to Adriatic Sea (Pountiers, 1987). However, this form has been reported as a commercial species in the area of Thessaloniki Gulf (North Western Aegean Sea), where it coexists with *F. glaber* (Zenetos, 1996; Galinou-Mitsoudi & Sinis, 2000). According to these authors, the occurrence ratio of *F. glaber* to *F. proteus* in three random fisheries samples of 99, 130 and 120 individuals in total was 0.74, 1.28 and 6.50, respectively. Besides Thessaloniki Gulf, *F. proteus* is found in Ionian Sea (Amvrakikos and Korinthiakos Gulfs) and also in Aegean Sea (Pagasitikos Gulf , N. Evoikos Gulf , Saronikos Gulf , Lesvos Island and Lemnos Island) (Koutsoubas et al., 2007; Zenetos, 1996) (Fig. 1).

Fig. 1. *F. glaber* distribution in Mediterranean and Black Sea. In inlaid map of Greece the *F. proteus* distribution is denoted, according to Zenetos (1996).

These commercial scallops are major target species due to their high demand in the national and European market. Nevertheless, the species seems to be overexploited, as the annual Hellenic production from over 20 t between mid 1970s and late 1980s, was reduced to 5 t from the late 1980s to 1990s (Koutsoubas et al., 2007). However, *Flexopecten* scallops fishing is forbidden in the Thessaloniki Gulf since 2002, due to the presence of high concentrations of heavy metals (Cd), while the stocks in the central Aegean Sea have rather collapsed in 2003 (Koutsoubas et al., 2007).

The two forms of *F. glaber* and *F. proteus* are also exploitable in Adriatic Sea (Pujolar et al., 2010). Besides the fishing, *Flexopecten* scallops having high growth rate, high demand and good price/kg, are also potential species for aquaculture.

Mitochondrial DNA (mtDNA) has been shown to be useful for analyzing relationships among bivalve populations (Hare & Avise, 1996; Rawson & Hilbish, 1998; Katsares et al., 2008), due to its maternal inheritance, its haploid nature and the fact that its effective population size is the one fourth of that of the nuclear DNA. The invertebrate mitochondrial 16S rDNA gene has been largely used for studying the population structure and the levels of genetic variation in many Pectinidae taxa (Kong et al., 2003; Mahidol et al., 2007; Yuan et al., 2009; Pujolar et al., 2010). As the Aegean populations of *F. glaber* and *F. proteus* are the main commercial stocks of these bivalves in Greece, the main objective of our study was to conduct a survey on the genetic resources of the two taxa using mitochondrial 16S rDNA nucleotide sequences.

Fig. 1. *F. glaber* distribution in Mediterranean and Black Sea. In inlaid map of Greece the *F.* 

These commercial scallops are major target species due to their high demand in the national and European market. Nevertheless, the species seems to be overexploited, as the annual Hellenic production from over 20 t between mid 1970s and late 1980s, was reduced to 5 t from the late 1980s to 1990s (Koutsoubas et al., 2007). However, *Flexopecten* scallops fishing is forbidden in the Thessaloniki Gulf since 2002, due to the presence of high concentrations of heavy metals (Cd), while the stocks in the central Aegean Sea have rather collapsed in

The two forms of *F. glaber* and *F. proteus* are also exploitable in Adriatic Sea (Pujolar et al., 2010). Besides the fishing, *Flexopecten* scallops having high growth rate, high demand and

Mitochondrial DNA (mtDNA) has been shown to be useful for analyzing relationships among bivalve populations (Hare & Avise, 1996; Rawson & Hilbish, 1998; Katsares et al., 2008), due to its maternal inheritance, its haploid nature and the fact that its effective population size is the one fourth of that of the nuclear DNA. The invertebrate mitochondrial 16S rDNA gene has been largely used for studying the population structure and the levels of genetic variation in many Pectinidae taxa (Kong et al., 2003; Mahidol et al., 2007; Yuan et al., 2009; Pujolar et al., 2010). As the Aegean populations of *F. glaber* and *F. proteus* are the main commercial stocks of these bivalves in Greece, the main objective of our study was to conduct a survey on the genetic resources of the two taxa using mitochondrial 16S rDNA

*proteus* distribution is denoted, according to Zenetos (1996).

good price/kg, are also potential species for aquaculture.

2003 (Koutsoubas et al., 2007).

nucleotide sequences.

*Chlamys proteus* or *F. proteus* Dillwyn has been considered since long, as a species of the bivalve family Pectinidae (Cossignani et al., 1992; Delamotte & Vardala–Theodorou, 1994; Doneddu & Trainito, 2005; Repetto et al., 2005; Zenetos et al., 2005). The majority of these sources mention that *F. proteus* is another similar species to *F. glaber*. The main systematic characteristic for the recognition of the two pectinids, is the difference in the number of major and dominated ribs which are 9-12 in *F. glaber*, but only five in *F. proteus* (Fig. 2). On the other hand, according to Poppe & Goto (1993), CLEMAM & ERMS, *F. proteus* is accepted as a subspecies or a form of *F. glaber*. Also, Raines & Poppe (2006) underline that *F. proteus* "is treated only as a synonyme" of *F. glaber.*

Fig. 2. Fished scallops in the study area of the two *Flexopecten* forms *proteus* and *glaber,* with epibiots on their left valves

Many biologists have argued that the future of descriptive taxonomy will depend on successfully embracing new techniques. Many ideas have been proposed and much progress has been achieved by using molecular data that provide a complementary approach to discriminate species separated by subtle morphological characters (Knowlton, 1993; Avise, 1994; Chan & Chu, 1996; Sarver et al., 1998; Mathews et al., 2002; Goetze, 2003). The invertebrate mtDNA 16S rDNA gene has been relatively well studied due to availability of universal primers (Kocher et al., 1989; Palumbi, 1996) and was used to resolve taxonomic problems in the family Mytilidae (Rawson & Hilbish, 1995), Veneridae (Canapa et al., 1996) and Pectinidae (Canapa et al., 2000a; Saavedra & Pena, 2004; Pujolar et al., 2010).

Taking into account all the existed considerations and the uncertain systematic status of these two common *Flexopecten* "forms", another aim of our work was an attempt to solve the identification problem of the two Aegean taxa, using the sequence analysis of the mtDNA 16S rDNA gene. A parallel and similar study (Pujolar et al., 2010), was also made for the Adriatic populations of the *Flexopecten* complex.
