In order to examine the stock management unit of the slime flounder Microstomus achne, this study estimated the population structure of this species on the basis of sequence variations of 480 base pairs of the mitochondrial control region and morphological variations in three meristic counts of dorsal, anal, and pectoral fin-rays. High genetic diversity of this species in the mitochondrial control region was observed, but no genetic differentiation was detected between individuals from the Sea of Japan and the Pacific Ocean. On the other hand, the number of dorsal and anal fin-rays differed significantly between individuals from those two regions, with Pacific individuals having a higher number of fin-rays. The pelagic larval period of this species is very long (about 85 days), and although dispersal in the early life stage has resulted in gene flow between the Sea of Japan and the Pacific Ocean, the migration range after settlement is relatively limited, suggesting that migration between the Sea of Japan and the Pacific Ocean is restricted. Thus, these results suggest that it is necessary to distinguish between the Sea of Japan and the Pacific Ocean as a stock management unit for this species.

　This study examined the use of defatted black soldier fly Hermetia illucens (BSF) meal as a fish meal substitute at high dose. Six-week feeding trials were conducted on juvenile red sea bream Pagrus major using experimental diets in which half or all of the fish meal in the control diet was substituted with defatted BSF larvae or prepupae meal. The larvae-fed groups showed higher feed efficiency, apparent protein retention and apparent fat retention than the control group. The group fed the diet containing younger larvae tended to have higher feed efficiency, apparent nutrient retention and apparent digestibility of protein and fat compared to fish fed aged larvae. However, daily feed intake was lower in several larvae-fed groups than in the control group. Lower concentration of total protein, blood urea nitrogen and total cholesterol in the plasma was observed in the larvae-fed groups than in the control group.

　We investigated the occurrence of the harmful dinoflagellate Karenia mikimotoi and environmental factors affecting red tide occurrence. The study was conducted in southern Harima-nada, eastern Seto Inland Sea, Japan from June to August 2022. K. mikimotoi red tide developed rapidly after a temporary increase in the DIN concentration below 10 m due to stratification caused by strong southeasterly winds in late July and rainfall in early August. The high-density area of K. mikimotoi red tide expanded from the eastern Shodoshima sea area, where higher cell densities were first recorded, to the aquaculture fishing grounds along the Shikoku coast due to wind and residual tidal currents. In Matsubara-Ura, K. mikimotoi reached densities of up to 7,233 cells/mL, resulting in the death of 19,900 tiger puffer fish Takifugu rubripes aged 1 to 2 years.

　The main taxonomic categories of species released, and habitat into which species were released, for each of 470 inland water fishery cooperatives (IWFCs) throughout Japan were extracted and categorized from IWFC business reports for 2017. IWFCs for which a high ratio of their total income was generated from recreational fishing license fees were extracted from these 470 IWFCs. Of these, 47 (10%) were identified as high-ranking, for which we analyzed the characteristics of their recreational fisheries. Compared with other IWFCs, these 47 highest-ranking IWFCs mainly released Japanese smelt Hypomesus nipponensis or Japanese crucian carp Carassius cuvieri into lake and marsh habitats. Many (85.1%) of these 47 IWFCs were located within or adjacent to heavily populated prefectures, or they were located in prefectures that were easily accessible from some heavily populated prefectures.