White trevally Pseudocaranx dentex is a high-value carangid fish species that is only cultured in Japan under full lifecycle aquaculture conditions. To make the reproductive process successful and efficient, sexual phenotyping of broodstock is essential, and this has conventionally been practiced via examination upon abdominal compression. However, in certain cases, sexual phenotyping is not successful due to unsuccessful sperm or semen collection, which leads to misclassification of the phenotype. This study identified the male characteristic DNA sequence of P. dentex. The pectoral fins of eight male and eight female 6-year-old F3 generation broodstock fish were utilized for male sex hormone quantification to determine each sex phenotype. The same fish DNA samples were subjected to bulked-amplified fragment length polymorphism (AFLP) screening, and a male characteristic AFLP DNA fragment of 227 bp in size was identified. A male characteristic fragment was also confirmed by second amplification when it was performed individually. All eight males used for screening carried the AFLP fragment, while none of the eight females did. AFLP was conducted for all 40 broodstock, and it was determined that all 24 putative males were AFLP positive, and 4 of the 16 putative females were AFLP positive. These results indicate that P. dentex may have a male characteristic DNA polymorphism. The nucleotide sequence of the male characteristic fragment showed high homology to Atlantic horse mackerel Trachurus trachurus chromosome 5, and the sequence did not have clear homology to known coding genes. Further studies are required to identify the sex-determining gene of P. dentex in the vicinity of the DNA sequence identified in this study.
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