Gonad histological observation and multilocus microsatellite analysis in a sample of Mediterranean sea bass Dicentrarchus labrax (Linnaeus, 1758) intended for breeding: a preliminary study

To evaluate gonadal differentiation and multilocus microsatellite variability, 13 Dicentrarchus labrax (S1-S13) intended for breeding were sampled at 290 dpf (day post fertilization) and sacrificed for gonad and muscle sampling. On gonad samples, sex differentiation was assessed by histological analysis. On muscle samples, nine microsatellite loci (DLA0008, DLA0119, DLA0016, DLA0020, DLA0105, DLA0145, DLA0248, DLA0228 and DLA0244) were analyzed. The histological analysis showed a full gonadic differentiation in ovary in 3 fish, gonad at early sexual differentiation towards the male line in 1 fish, gonads fully differentiated in testis in 7 fish, gonads with intratesticular oocytes in 2 fish. Microsatellite analyses revealed the existence of 10 different genotypes. Diversity index of each locus varied from 0.61 for the microsatellite DLA0020 to 0.88 for microsatellite DLA0008. By combining the 9 microsatellite markers, a high discriminatory power (ID = 0.95) was found making this method useful to differentiate among the samples and to detect genetic micro variations. Further insights into a greater group of subjects and a larger number of molecular markers are worth exploring in cultured Dicentrarchus labrax in order to develop more quantitative trait loci to establish genetic linkage maps and correlate the genetic variability with the gonad differentiation of this fish species.