The first chromosomal characteristics of nucleolar organizer regions (NORs) and karyological analysis of triangle butterflyfish (Chaetodon triangulum) and yellow butterflyfish (C. andamanensis) from Andaman Sea, Phuket and Phang Nga Province, Thailand, were studied. Kidney cell samples were taken from five male and five female fish. Mitotic chromosome preparations were conducted using standard squash technique as well as taken directly from kidney cells. Metaphase spreads were performed on microscopic slides and then airdried. Conventional and Ag-NOR banding techniques were applied to stain the chromosome. The results showed that the diploid chromosome number of C. triangulum and C. andamanensis was 2n=48, and the fundamental numbers (NFs) were 48 and 52, respectively. Karyotpes were present as 46 large telocentric and two medium telocentric chromosomes in C. triangulum; and 2 large metacentric, 8 large telocentric, 34 medium telocentric, 2 medium acrocentric, and 2 small telocentric chromosomes in C. andamanensis. No strange sized chromosomes related to sex were observed. After the Ag-NOR banding technique, one pair of NORs was observed on the long arm centromeric region of large telocentric chromosome pair 21 in C. triangulum and on the long arm subcentromeric region of the largest metacentric chromosome pair 1 in C. andamanensis. The karyotype formulas are as follows:

We report the first chromosome analysis in the Indian vagabond butterflyfish (Chaetodon decussatus) and lined butterflyfish (C. lineolatus) from Andaman Sea, Phuket Province, Thailand. Kidney cell samples were taken from four male and four female fishes. The mitotic chromosome preparation was directly prepared from kidney cells. The chromosomes were stained with conventional and Ag-NOR staining techniques. The results showed that the diploid chromosome number of C. decussatus and C. lineolatus was 2n=48, and the fundamental number (NF) was 48 in both males and females. The chromosomes were present as large telocentric and medium telocentric chromosomes in numbers of 24-24 and 22-26, respectively. There was no observation of strange size chromosomes related to sex. After Ag-NOR banding technique, a single pair of nucleolar organizer regions (NORs) was observed on the long arm centromeric region of medium telocentric chromosome pair 18 in C. decussatus and on the long arm subcentromeric region of medium telocentric chromosome pair 17 in C. lineolatus. The karyotype formulas could be deduced as: