The first chromosome analysis and nucleolar organizer region (NOR) pattern of the humpback cardinalfish (Fibramia lateralis) were studied. Samples from 10 male and 10 female fish were collected from the Andaman Sea and Gulf of Thailand. Mitotic chromosome preparations were prepared directly from kidney tissues. Conventional and Ag-NOR staining techniques were applied to stain the chromosomes. The results showed that the diploid chromosome number of F. lateralis was 2n=46, and the fundamental numbers (NF) were 54 in both sexes. The karyotype consisted of 8 large acrocentric, 12 large telocentric, 24 medium telocentric and 2 small telocentric chromosomes. Moreover, the results indicated that the region adjacent to the telomere of the short arm of the second acrocentric chromosome pair showed clearly observable nucleolar organizer regions (NORs). Strange size chromosomes related to sex were not observed. The karyotype formula for F. lateralis is as follows: a t t t 8 12 24 2 2 (diploid) 46=L +L +M +S n

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Summary This is the first heteromorphic nucleolar organizer regions (NORs) and chromosome analysis of Rolland s demoiselle (Chrysiptera rollandi). Kidney cell samples were taken from five male and five female fish. Mitotic chromosome preparations were prepared directly from kidney cells. Conventional and Ag-NOR staining techniques were applied to stain the chromosomes. The results showed that the diploid chromosome number of C. rollandi was 2n=46, and the fundamental number (NF) was 50 in both males and females. The types of chromosomes were 2 large submetacentric, 2 large telocentric, 2 medium acrocentric, 32 medium telocentric, and 8 small telocentric chromosomes. In addition, the short arm of acrocentric chromosome pair 2a and the long arm of telocentric chromosome pair 6a (non-homologous chromosome) showed clearly observable NORs heteromorphic (2a6a) in both sexes and chromosome size was not related to sex. The karyotype formula for C. rollandi was:2n (