CYTOGENETIC ANALYSIS OF GILTHEAD SEABREAM SPARUS-AURATA (PISCES, PERCIFORMES), A DELETION AFFECTING THE NOR IN A HATCHERY STOCK

We have cytogenetically characterized a hatchery stock of gilthead sea bream, Sparus aurata. The study included larvae, juveniles and adults. In S. aurata (diploid chromosome number 2n = 48), a pair of NORs is l ocated at the ends of the short arms of the first submetacentric pair of chromosomes. In this stock we discovered a polymorphism which affec ts the NORs, and, by means of several cytogenetic and molecular techni ques, we demonstrate that this polymorphism is due to the complete del etion of one of the two NORs in a high number of individuals. The sign ificance of these cytogenetic characteristics for this species are dis cussed since they may be the source of aquaculture problems.