Comparative cytogenomic analysis of Cardinal fishes (Perciformes, Apogonidae) from Thailand

Cardinal fishes (Apogonidae) belong to the numerically dominating reef fish families. Many species are kept in the aquarium and are popular as small, peaceful, and colorful fish. The taxonomic status of this family remains debatable. Up to the present, there are 366 valid species. However, only 15 species were studied cytogenetically including one by molecular cytogenetics. Here we report characterization of four cardinal fishes, namely Fibramia lateralis , Pterapogon kauderni , Sphaeramia nematotera and S. orbicularis from the Gulf of Thailand using different cytogenomic approaches. Chromosome preparations from kidney were studied by conventional staining, Ag-NOR banding and molecular cytogenetics by fluorescence in situ hybridization (FISH) using 18S rDNA and microsatellite d(CA) 15 probes. Whereas, all species had the same diploid chromosome number as 2 n = 46, but there were differences in the fundamental number (NF) and chromosome structure: F. lateralis (NF = 54; 8a + 38t), S. nematotera (NF = 74; 14sm + 14a + 18t), S. orbicularis (NF = 68; 8sm + 14a + 24t) and P.kauderni (NF = 92; 4 m + 14sm + 28a). In all four species, NORs and 18S rDNA signals were detected adjacent to the telomere on the short arm of an acrocentric chromosome pair, but on different chromosome pairs, as 2, 10, 7 and 13 in F. lateralis , S. nematotera , S. orbicularis and P.kauderni , respectively. Also, microsatellite d(CA) 15 sequences showed specific hybridization patterns along the chromosomes of the four studied species. Accordingly, all four Apogonidae species studied were clearly distinguishable by cytogenetic and molecular hybridization procedures. Further studies with more species are needed to explore their systematic status in the family