Multiple spawning of captive Pacific bluefin tuna (Thunnus orientalis) as revealed by mitochondrial DNA analysis

Sequence analysis targeting the hypervariable mitochondrial DNA-D-loop region was performed to survey spawning patterns of captive Pacific bluefin tuna (Thunnus orientalis). The broodstock consisted of approximately 100 individuals. Sampling of fertilized eggs was conducted for ten days within three weeks in 2007. Among 236 eggs and 31 juveniles analyzed, 25 unique haplotypes were detected, indicating that more than 25 female parents participated in reproduction in the fish cages. Among the 25 haplotypes, 10 were found at relatively high frequencies. Some of these haplotypes were observed to occur at 2 to 3 consecutive days, indicating that the captive bluefin tuna females were capable to consecutively spawn multiple times.