Anecdotally, it is considered that there are several populations for the cultured tiger pufferfish, Takifugu rubripes, in Japan; however, strict pedigree managements are not undertaken in hatcheries. To understand the genetic diversity and relationship among broodfish used in Nagasaki Prefecture, where the majority of aquaculture seedlings of this species are produced, genetic analysis was conducted using 12 microsatellite markers. DNA samples and pedigree information of each broodfish used for production in 2015 and 2016 were collected from private hatcheries. Samples from a total of 56 broodfish including 15 wild females were obtained. The artificially raised broodfish were grouped into three putative populations, Population A-C, based on pedigree records. The results of several genetic statistics showed significant genetic divergence from wild individuals among the populations. Population structure analysis revealed genetic independency of Population B and Population C, while it was implicated that Population A was occasionally interbred and crossbred with wild individuals, suggesting the susceptibility of population loss of Population A. Moreover, discordance in population assignments was observed between pedigree records and what inferred from molecular markers. These results indicated the necessity of pedigree managements with the aid of molecular markers for the sustainable use of these populations.

In salmonids, hybrids derived from three -species or subspecies may be new breeding resources because hybrids between two salmonid species have been observed to reach maturity. However, the characteristics of three -species or -subspecies hybrid are unknown. Thus, we produced four families of three -subspecies F₂ hybrids by artificially crossbreeding F₁ hybrids (amago salmon (Oncorhynchus masou ishikawae) × biwa salmon (Oncorhynchus masou subsp.)) and F₁ hybrids (amago salmon × masu salmon (Oncorhynchus masou masou)). We bred the three -subspecies F₂ hybrids in fresh water for two years and we investigated their survival, growth, and fertility. The survival rates at hatching and from 5 to 12 months after fertilization were from 84.1 to 95.1% and from 97.2 to 98.8%, respectively, for four families of the three -subspecies F₂ hybrids. The body weights and body lengths 12 months after fertilization were from 214.8 to 248.2 g and from 23.4 to 24.1 cm, respectively, for four families of the three -subspecies F₂ hybrids. The percentage of mature individuals 24 months after fertilization were from 97.6 to 100.0% for four families of the three -subspecies F₂ hybrids. Furthermore, we produced three -subspecies F₃ hybrids by crossing four families of the three -subspecies F₂ hybrid female and male with more than about 1.5 kg or 1.0 kg body weight, respectively. These results indicate three -subspecies hybrids will be useful as new salmonid breeding resources.

Chub mackerel (Scomber japonicus) and blue mackerel (Scomber australasicus) are important commercial fishes around the coastal waters of Japan. In this study, a novel polymerase chain reaction (PCR)-based species identification method was developed and used to discriminate between these two species and their hybrids. In this PCR method, a species-specific insertion or deletion marker is used to enable the amplification of the same locus in two Scomber species with one set of primers. The size difference in the amplified DNA fragment was approximately 300 bp, and the fragments could be separated using standard agarose gel electrophoresis. To validate the effectiveness of the method, the two mackerel species were sampled in various areas of Japan and identified using PCR. In 208 chub mackerel and 118 blue mackerel, PCR-based identification was 100% consistent with external morphology-based species identification. Moreover, in DNA samples of F1 hybrid larvae obtained via artificial insemination of the two mackerel species, hybrids were identified with 100% accuracy using the PCR method. Chub mackerel, blue mackerel, and their hybrids are typically difficult to identify by their morphological characteristics. Thus, our PCR method will help in identifying these fishes and will contribute to assessing mackerel stocks in Japan.