There are numerous means to improve the tilapia aquaculture industry, and one is to develop disease resistance through selective breeding using molecular markers. In this study, 11 disease-resistance-associated microsatellite markers including 3 markers linked to hamp2, 4 linked to hamp1, 1 linked to pgrn2, 2 linked to pgrn1, and 1 linked to piscidin 4 (TP4) genes were established for tilapia strains farmed in Taiwan after challenge with Streptococcus inae. The correlation analysis of genotypes and survival revealed a total of 55 genotypes related to survival by the chi-square and Z-test. Although fewer markers were found in B and N2 strains compared with A strain, they performed well in terms of disease resistance. It suggested that this may be due to the low potency of some genotypes and the combinatorial arrangement between them. Therefore, a predictive model was built by the genotypes of the parental generation and the mortality rate of different combinations was calculated. The results show the same trend of predicted mortality in the offspring of three new disease-resistant strains as in the challenge experiment. The present findings is a nonkilling method without requiring the selection by challenge with bacteria or viruses and might increase the possibility of utilization of selective breeding using SSR markers in farms.

In this study, genetic characteristics of four tilapia strains including NOVIT4, 13th GIFT generation, China and Philippine were investigated by analysis the genotype at 6 microsatellite loci. It was found that all loci showed high polymorphism with 51 identified alleles, in which GM139 and UNH995 loci were the highest polymorphism with the appearance of 14 and 11 alleles, respectively. Deficiency of expected heterozygosity occurred in all tilapia strains, the Ho value of which was lower than the He one. Besides, 17/24 loci were significantly different from the Hardy-Weinberg principle (P < 0,05). The Fst ranging from 0.012 to 0.025 indicated that the genetic difference among populations was small. However, the analysis of molecular variance (AMOVA) showed that the genetic diversity at the molecular level among individuals within the same population and among individuals were high, corresponding to 36.69% and 61%, respectively. The findings of this study are useful in term of giving the genetic information of four Nile tilapia strains for the selective breeding program.

The genetic diversity of five natural populations of milkfish (Chanos chanos) collected in Nghe An, Quang Binh, Binh Dinh, Phu Yen, Khanh Hoa provinces in Vietnam was examined using COI gene sequence analysis. Twelve haplotypes were noted from a total of 50 sequences along with 12 variable sites and 6 parsimony informative sites. The Quang Binh milkfish population had the highest haplotype (0.889 ± 0.060) and nucleotide diversities (0.00301 ± 0.00049). Overall, haplotype and nucleotide diversities were 0.804 ± 0.036 and 0.00212 ± 0.00026, respectively. Genetic differentiation (FST) was high between the milkfish populations of Nghe An – Quang Binh (0.21744) and Nghe An - Phu Yen (0.26215). Haplotype network analysis indicated that milkfish populations shared common haplotypes and each population had its own private haplotypes. Population structure and demographic expansion were not evident for all populations except for Quang Binh. This is the first principal endeavor to understand genetic information of milkfish in Vietnam, thereby providing information for scientists, managers, and the general public to establish timely strategies to explore, protect, and develop milkfish genetic resources in the future.