Chromosome description and localization of NucleolusOrganizing Regions (NORs) by Ag-staining Technique inAlburnus filippii (Cyprinidae, Cypriniformes) in Anzali LagooNorth Iran

The silver staining procedure is commonly used to visualize the activity of ribosomal RNA genes, since it has been established that only those NORs of metaphase chromosomes that are functionally active during the preceding interphase are capable of staining (Galetti et al., 1984; Schmid et al., 2006). Nucleolus organizer regions (NORs) are used as markers to indicate intra- and inter-species chromosomal polymorphism in many groups of fish (Ra´b et al., 2008). There are no available reports specifying the activity of nucleolus organizer regions location in Kura bleak (A. filippii) chromosomes by silver staining. The aim of this paper is to present the chromosome complement, number and location of the nucleolar organizer regions (NORs) of A. filippii (Kessler, 1877), commonly known as Kura bleak from northern Iran, a survey initiated by Gul et al. (2006). The samples (six females and four males) were collected in 2006 from Anzali Wetland (37?28ʹN, 49?27ʹE) Guilan, Iran. The fish were alive transported to the laboratory and were kept for 72 h prior to processing (Pourkazemi et al., 2010). The preparation of chromosomes was performed according to Collares- Pereira et al. (1998) but reducing the colchicine incubation time. Detection of the nucleolus organizer regions (NORs) was done following the silver staining method of Howell and Black (1980) with slight modifications to reveal the presence of active rDNA clusters. In the present study the number of diploid chromosomes were 2n=50, of which six pairs were metacentric (M), 9 pairs were submetacentric (Sm), 4 pairs were subtelocentric (St) and 6 pairs were acrocentric (a). The chromosomes are arranged in decreasing size. In this metaphase the fundamental number (number of chromosome arms) was therefore 88 and no heteromorphic sex chromosomes were observed. Nucleolar organizer regions (NORs) were observed at the end of the short arms of one pairs of medium-sized subtelocentric chromosomes. NOR locations in A. filippii are presented in Figure1.