Chromosomal fusion in Brazilian populations of Trinectes inscriptus Gosse, 1851 (Pleuronectiformes; Achiridae) as revealed by internal telomere sequences (ITS)

• We provide the first cytogenetic report about Trinectes inscriptus.
• This is a rare example of detailed cytogenetic studies in marine fish populations.
• Internal telomere sequences were observed, evidencing chromosomal rearrangements.

Flatfish (Pleuronectiformes) are one of the few examples of marine fish with remarkable chromosomal variation. Nonetheless, cytogenetic data in species of this order are still scarce and population approaches have been neglected. Therefore, a detailed karyotypic survey was carried out for the first time in Trinectes inscriptus along northeastern and southeastern Brazil. All specimens shared 2n = 42 with a karyotype composed of eight metacentric/submetacentric and 34 subtelocentric/acrocentric chromosomes, differing from the basal condition of marine teleosteans (48 acrocentric chromosomes). Heterochromatin was restricted to the pericentromeric region of most chromosomes, short arms of a few pairs and coincident with GC-rich sites at NORs. Fluorescence in situ hybridization (FISH) using 18S and 5S rDNA probes revealed synteny between both rDNA classes at pair 5 in all samples. Telomeric sequences were mapped at terminal sites of most chromosomes as well as at centromeric region of the second pair. The derived karyotype macrostructure reported in T. inscriptus (low 2n, presence of large biarmed chromosomes) has probably evolved from chromosomal fusions, as reinforced by the presence of internal telomere sequences (ITS) in a large metacentric pair, besides inversions and heterochromatin accumulation. Since this pattern of genomic organization was stable among collection sites (up to 1000 km apart), we suggest these rearrangements have taken place in the beginning of species diversification.