Abstract:“Yuemin No.1” is a novel holandric species of tilapia, which was bred with Oreochromis niloticus and O. aureus. In order to reveal the genetic characteristics of tilapia “Yuemin No.1,” the genetic diversity, genetic structure, and genetic relationships among groups of tilapia “Yuemin No.1” and its breeding populations were studied by isozyme electrophoresis and sequence analysis of the D-loop region of mtDNA. The results of isozyme electrophoresis showed that the zymogram of esterase (EST) and lactate dehydrogenase (LDH) were population- and tissue-specific in tilapia. The expression level of EST in the muscle and spleen was extremely low, whereas that in the liver was high. LDH was highly expressed in all the tissues, as revealed by the different zymograms. Ten bands of EST and five of LDH were detected in tilapia “Yuemin No.1” and its breeding populations. The proportion of polymorphic loci (P) ranged from 12.50% to 71.43%, the average observed heterozygosity (Ho) ranged from 0.0417 to 0.6143, and the Hardy-Weinberg genetic deviation index (D) ranged from ‒0.2347 to 0.9072. The result of sequence analysis of the D-loop region of mtDNA revealed that no significant difference occurred in base composition, and that A+T content (63.39%) bias was widespread in all the populations. There were 20 haplotypes in tilapia “Yuemin No.1” and its breeding populations. The nucleotide diversity index (Pi) ranged from 0 to 0.0519. The Pi value of WY1, XX, XY2, and XY populations (0.0440~0.0519) were significantly higher than that of YY1, YY2, and WZ populations (0~0.0009). The genetic differentiation index (FST) among populations ranged from ‒0.0115 to 0.9963. There was no significant genetic differentiation (FST<0.05, P>0.01) between the XY2 and WY1, XX and XY, and WZ and YY2 populations. The average genetic distance between XY2 population and O. niloticus (XX and XY populations) was 0.0639, whereas that between the XY2 population and O. aureus (WZ population) was 0.0695. Cluster analysis revealed two clusters; one cluster included XY, XX, YY1, and XY2 populations, and the other cluster included WY1, WZ, and YY2 populations. This study revealed the biochemical and molecular genetic features of tilapia “Yuemin No.1,” and provide research data for germplasm identification, establishment of breeding populations, and maintainence of stable inheritance of desirable traits.
