Cytogenetic characteristics of the round goby Neogobius melanostomus (Pallas, 1814) (Teleostei: Gobiidae: Benthophilinae)

Abstract

Karyotype and cytogenetic characteristics of the invasive round goby (Neogobius melanostomus (Pallas, 1814)) from the population inhabiting the Gulf of Gdansk, Baltic Sea, Poland were investigated using conventional and molecular cytogenetic techniques. The diploid chromosome number of all samples was 2n = 46 and the karyotype consisted of subtelo-to acrocentric chromosomes that gradually decreased in size. Analysis of chromatin resistance to restriction enzymes (Alu I and Dde I) showed pericentromeric and telomeric blocks of heterochromatin. Nucleolus Organizer Regions (NORs) were observed in the pericentromeric regions of two medium-sized chromosomes. Sequential staining (DAPI, CMA3 and AgNO3) showed that the NORs are DAPI-negative and CMA3-positive in round goby chromosomes. Additionally, DAPI-negative and CMA3-negative chromatin was identified in the interstitial position of two chromosomes. Fluorescent In Situ Hybridization (FISH) with a telomeric probe did not reveal any Interstitial Telomeric Repeat sequences (ITRs). No morphologically differentiated sex chromosomes were found in the round gobies studied. Considering the increased numbers of bi-armed chromosomes to be a derived condition in some ‘neogobiin’ species, the round goby karyotype of 46 mono-armed chromosomes, which are similar in both female and male cells and have GC-rich NOR-related regions located on the single chromosome pair, fits as an ancestral Neogobius karyotype pattern.