No abstract

Specimens from two freshwater populations of the ninespine stickleback Pungitius pungitius in Poland showed morphologically differentiated sex chromosomes. A heteromorphic pair of chromosomes appeared only in male diploid cells. The Y chromosome was the largest chromosome in the P. pungitius karyotype.

The aim of the present study was to produceAcipenser baeri  (Huso huso  Acipenser ruthenus) hybrids in a diploid and triploid state and to study their viability in comparison with the A. baeri from the ¢sh farm stock. A heat shock (37 1C) in the 18th minute after fertilization was applied to induce triploidy. The survival rate and the ploidy level of the hybrids obtained were studied. The mortality of triploid hybrids was approximately twice as high as the mortality of diploid hybrids. No signi¢cant di¡erence in the survival rate between Siberian sturgeon and their diploid hybrid with bester was noted. Cytogenetic analysis was performed by preparing chromosomes from the gill epithelium. The results showed that all studied ¢sh from the heat-shocked group were triploid.

During the last 10 years, the stickleback has emerged as a promising model system in several biological fields. In particular, it is one of the most investigated fish groups by evolutionary biologists, as a model for understanding the genetic and molecular basis in processes of adaptive radiation, microevolution and development, as well as the genetic basis of sex determination. To provide karyological information about stickleback fish we performed cytogenetic analysis of the threespine stickleback (Gasterosteus aculeatus L.) and the ninespine stickleback (Pungitius pungitius L.). Diploid chromosome number in both species equalled 42; however, the chromosome arm numbers were 62 and 70, respectively. In the threespine stickleback, multichromosomal location of silver (AgNO 3 ) and chromomycin A 3 (CMA 3 ) positively stained Nucleolar Organizer Regions (Ag/CMA 3 -NORs) was observed. The number of silver-stained chromosomes varied among different individuals from two to six. The Ag/CMA 3 -NORs covered almost entire short arms of one pair of middle-sized submetacentric chromosome pairs in the ninespine stickleback. In one male, the only Ag-NOR was situated telomerically on the long arm of the Y chromosome. The 5S rDNA clusters were observed on short arms of one pair of subtelocentric chromosomes in the threespine stickleback and four pairs of subtelo-acrocentric chromosomes in the ninespine stickleback of both sexes. Chromosome rearrangements responsible for the stickleback karyotype polymorphisms did not leave any internally located telomeric sequences. The results obtained in two stickleback species are therefore of considerable interest and further karyological studies should be carried out on the other populations of the wide species range in order to provide a more general picture of karyoevolutive trends in Gasterosteidae.

Chromosome preparations and assay of the microsatellite locus Afu-68 were used to determine ploidy in Siberian sturgeon (Acipenser baeri Brandt) and F 1 hybrids of Siberian sturgeon and Russian sturgeon (Acipenser gueldenstaedti Brandt). The chromosome number and microsatellite locus Afu-68 were compared and these analyses were used for identi¢cation of 'haploid', 'diploid' and 'triploid' progeny of the studied cross of A. baeri  (A. baeri  A. gueldenstaedti).