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We constructed a second-generation linkage map of tilapia from the [F.sub.2] progeny of an interspecific cross between Oreochromis niloticus and Oreochromis aureus. The map reported here contains 525 microsatellite and 21 gene-based markers. It spans 1311 cM in 24 linkage groups, for an average marker spacing of 2.4 cM. We detected associations of sex and red color with markers on linkage group 3. This map will enable mapping and selective breeding of quantitative traits important to the economic culture of tilapia as a food fish and will contribute to the study of closely related cichlids that have undergone explosive adaptive radiation in the lakes of East Africa.

The genetic relationships of two subspecies of striped field mice of Korea are discussed. The two species, Apodemus agrarius coreae and Apodemus agrarius chejuensis, are morphologically distinct. A. agrarius coreae was found to have more genetic diversity than the other species. Data do not support the concept that the two morphotypes are two species. The two morphotypes do not share mitochondrial haplotypes. Likely little gene flow between the two exists. The subspecies might have been separated at the time of separation of islands from the mainland. Wan Island A. agrarius coreae with large body size cluster with the large-bodied A. agrarius chejuensis based on phylogenetic analysis.

We have constructed a genetic map for a tilapia, Oreochromis niloticus, using DNA markers. The segregation of 62 microsatellite and 112 anonymous fragment length polymorphisms (AFLPs) was studied in 41 haploid embryos derived from a single female. We have identified linkages among 162 (93.1%) of these markers. 95% of the microsatellites and 92% of the AFLPs were linked in the final map. The map spans 704 Kosambi cM in 30 linkage groups covering the 22 chromosomes of this species. Twenty-four of these linkage groups contain at least one microsatellite polymorphism. From the number of markers 15 or fewer cM apart, we estimate a total map length of [approximately]1000-1200 cM. High levels of interference are observed, consistent with measurements in other fish species. This map is a starting point for the mapping of single loci and quantitative traits in cichlid fishes.

The determination of the complete sequence of the mitochondrial genome of the sea lamprey, Petromyzon marinus reveals that it consists of genes for 13 proteins, 22 tRNAs and two rRNAs. The genome is 16,201 bp in length. The transcriptional polarities of the genes that code the 13 proteins are identical to those of the polarities of chordate mtDNAs.

We obtained 282 base pairs of sequence for the mitochondrial control region of 70 individuals of Korean striped field mice Apodemus agrarius coreae and Apodemus agrarius chejuensis to determine the levels of genetic divergence between these morphologically distinct taxa. The DNA sequences showed more genetic diversity (π) in A. agrarius coreae (2.98%) than in A. agrarius chejuensis (1.86%). Our data do not support the current concept that the two morphotypes are different species, but phylogenetic analysis indicates that animals of A. agrarius coreae with large body size from Wan Island cluster with the large-bodied A. agrarius chejuensis, and should be included in that taxon. As currently accepted A. agrarius coreae is not strictly monophyletic, because the large-bodied samples cluster within the range of mitochondrial variation of A. agrarius chejuensis. The fact that the two morphotypes do not share mitochondrial haplotypes (χ2=66, P < 0.001) suggests that there is little gene flow between them. A molecular clock estimate suggests that the two subspecies might have been isolated at the time of separation of the islands from the mainland. [ABSTRACT FROM AUTHOR]

Edwardsiella (E.) ictaluri is a major bacterial pathogen that affects commercially farmed striped catfish (Pangasius hypothalamus) in Vietnam. In a previous study, 19 strains of E. ictaluri collected from striped catfish were biochemically identified with an API-20E system. Here, the same 19 strains were used to assess the ability of matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS; applied using a MALDI Biotyper) to conduct rapid, easy and accurate identification of E. ictaluri. MALDI-TOF MS could directly detect the specific peptide patterns of cultured E. ictaluri colonies with high (＞ 2.0, indicating species-level identification) scores. MALDI Biotyper 3.0 software revealed that all of the strains examined in this study possessed highly similar peptide peak patterns. In addition, electrophoresis (SDS-PAGE) and subsequent immuno-blotting using a specific chicken antibody (IgY) against E. ictaluri revealed that the isolates had highly similar protein profiles and antigenic banding profiles. The results of this study suggest that E. ictaluri isolated from striped catfish in Vietnam have homologous protein compositions. This is important, because it indicates that MALDI-TOF MS analysis could potentially outperform the conventional methods of identifying E. ictaluri., Competing Interests: There is no conflict of interest.