Assessing the spawning season in common dentex (Dentex dentex) using microsatellites Yaisel J Borrell 1 , Gloria Blanco 1 , EmiliaVa Ł zquez 1 , Jorge A Pin ì era 1 , Gemma Gimenez 2 , Alicia Este¤ vez 2 & Jose A Sa Ł nchez 1 1 Laboratorio de Gene¤ tica Acu|¤ cola, Departamento de Biolog|¤a Funcional, Universidad de Oviedo, IUBA, Oviedo, Spain 2 Centro de Acuicultura-IRTA, Sant Carles de la Ra Ł pita,Tarragona, Spain Correspondence: J A Sa Ł nchez, Laboratorio de Gene¤ tica Acu|¤cola, Departamento de Biolog|¤a Funcional, Universidad de Oviedo, IUBA, 33071 Oviedo, Spain. E-mail: jafsp@uniovi.es Abstract A set of ¢ve variable microsatellite markers was used for the genetic characterization of two common dentex ( Dentex dentex ) broodstocks from an experimental hatchery and for the screening of the egg batches spawned during the complete spawn season in 2006. After parentage assignment, simulations were per- formed for the hatchery 1 broodstocks; the microsatel- lite set correctly assigned over 93% of descendants to parents when one parent was known and 80% when neither parent was known. Of the 261 eggs that the DNA was correctly ampli¢ed from, 254 were success- fully assigned to a parental couple. More than one female or male took part (at the same point in time) in the spawning season. However, we observed ‘domi- nant’ individuals that produced high proportions of the descendants (unequal reproductive success) in all the sampling periods, although the contributions of these dominant individuals could change over time. This phenomenon reduces the e¡ective breeding num- bers, and could lead to inbreeding if this factor is not taken into account when the next parental generation is obtained. This factor should also be considered in aquaculture selection programmes because the dominant breeders may not be the most interesting individuals for commercial or productive schemes. Keywords: common dentex, aquaculture, microsa- tellite markers, mass spawning, parentage, inbreeding Introduction Fish are highly fecund, and there is a great tempta- tion to spawn as few ¢sh as possible in order to save money and labour in hatcheries. However, this strat- egy may increase the probability of inbreeding, and it may reach levels that signi¢cantly decrease growth rates or other production phenotypes (Kincaid1976, 1983; Gjerde, Gunnes & Gjedrem 1983; Sbordoni, De Matthaeis, Cobolli Sbordoni, La Rosa & Mattoccia 1986; Su, Liljedabl & Gall 1996). In addition, the loss of genetic variation (genetic drift) can make future selective breeding programmes ine¡ective (Bartley 1998; Tave 1999). The construction and maintenance of pedigrees have been di⁄cult to achieve in both wild and captive ¢sh populations. Until recently, in order to produce pedigree ¢sh progeny, the progeny groups had to be reared separately until they were large enough to be tagged using physical methods. This approach is cost-, space- and labour-intensive. However, several cultured ¢sh (e.g. sparids ¢sh) exhi- bit mass spawning events where the spawning dynamics (e.g. the critical number of ¢sh involved to induce the process, as well as the potential range of individual contributions to the spawning event) are unknown (Brown, Woolliams & Mcandrew 2005) and thus it is not possible to obtain pedigrees. Parentage assignment using microsatellites has been very useful previously in aquaculture. DNA microsatellites can be used for retrospective parental assignments and comparisons of the viability of o¡- spring with di¡erent parental origins without bias caused by unknown variations in laboratory systems or farm environments. Moreover, microsatellites make it possible to estimate the relatedness between pairs of individuals of unknown origins (Estoup, Gharbi, Sancristobal, Chevalet, Ha¡ray & Guyomard 1998; Norris, Bradley & Cunningham 2000; Selvamani, Degnan & Degnan 2001; Jackson, Martin-Robichaud Aquaculture Research, 2008, 39, 1258^1267 doi: 10.1111/j.1365-2109.2008.01988.x r 2008 The Authors 1258 Journal Compilation r 2008 Blackwell Publishing Ltd