Seasonal dynamics of the profundal zone（3.1-5.8 m depth）fish assemblage in Lake Kasumigaura, a large shallow inland-sea lake（220 km ²）in Ibaraki Prefecture, eastern Japan, were examined by monthly bottom trawl-net（mouth size 5.5 m and mesh size 3 mm）sampling from January 2014 to December 2015. A total of 14,840 individuals（mainly late juvenile and adult stages）representing 30 species in 12 families, including 3 commercially important and 2 threatened species, were collected throughout the study period. The mean number of fish species per haul varied from 6.7 to 12.7, with no apparent seasonal tendencies. Considerable seasonal fluctuations in mean numbers of individuals were found in each year（peak abundances > 400 ind. ⁄ haul in summer and winter seasons）, with species composition differing significantly between the two seasons. The most abundant species were Tridentiger brevispinis, Salangichthys microdon, Hypomesus nipponensis, Gnathopogon elongatus elongatus, Ictalurus punctatus, Carassius sp., Cyprinus carpio, Pseudorasbora parva, Acanthogobius lactipes, Gymnogobius urotaenia, Rhinogobius sp. and Squalidus chankaensis biwae, accounting for 98.3% of the total number of individuals. Seasonal changes in abundance and body size of each of the above species suggested that the profundal zone of Lake Kasumigaura is inhabited throughout almost the entire life history of some fishes（e.g., S. microdon and H. nipponensis）, being a dispersal area for early life stages from spawning and nursery grounds in littoral and riverine habitats, as well as an overwintering habitat for other species.

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Using data collected from 2004 to 2018, the relationships between fluctuation in water quality and river loads were analyzed in eight areas within Osaka Bay, comprising the A-, B-, and C-type areas as designated by the chemical oxygen demand（COD）environmental quality standards. Different trends were confirmed in each area, related to their location in the bay. Decreasing COD concentrations were observed around the Muko River mouth, while concentrations near the Yodo River mouth, near the Yamato River mouth, and in areas at the center of the bay remained unchanged. These stable trends might be attributable to the high COD concentrations in the inflow water at the inner part of the bay, as well as the in situ COD production in the center of the bay. In summary, changes in water quality reflecting river loads were observed in the inner part of the bay, but the effect decreased toward the center of the bay where in situ production might be greater. Therefore, for the future restoration plan in Osaka Bay, different approaches will be required, depending on the characteristics of the individual sea areas.

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The clupeid fishes, Konosirus punctatus and Sardinella zunasi, are dominant in the larval ichthyofauna of Ariake Sound, Shimabara Bay, where they spawn in spring and spring to summer, respectively. The distribution of two species larvae partly overlapped in the inner estuaries in spring. To clarify the early life histories of both species, the pelagic, demersal and immigrated stages were collected with larva nets, a beam trawl and a seine net, respectively, in Ariake Sound in May 2006 and 2019. While egg and larva distribution of both species spatially fluctuated between two years, both larvae were fundamentally observed to aggregate in the inner parts of the sound. K. punctatus and S. zunasi used the littoral zone and the inner estuaries as their nursery grounds, respectively, but they overlapped to inhabit some estuaries. Then, the vertical distributions of larvae in the estuary showed that K. punctatus was aggregated in the surface layer, and S. zunasi was dispersed during all tidal phases. Thus, there is likely less serious competition of larval niche during early larval period between two species in the estuaries.

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The occurrence patterns of the larval and juvenile gluttonous goby, Chaenogobius gulosus in Omori Furusato-no-Hamabe Park in the innermost portion of Tokyo Bay were investigated by monthly sampling. Four types of gear were used: a small seine net towed off the sandy beach and over the tidal flat between January 2015 and December 2018; basket nets placed at a wharf with a vertical seawall between January 2016 and December 2018; a hand net used at the wharf between January 2016 and December 2016; and a set net placed on the tidal flat and in the waterway from the tidal flat to a tidepool between January 2016 and December 2018. Ontogenetic intervals were determined from the morphometric characters of 274 specimens（3.93–41.7 mm body length［BL］）and the osteological characters of 92 cleared and stained specimens（3.93–25. 5 mm BL）. In total, 124 individuals（3.78–30.3 mm BL）were collected from the sandy beach, 447 （3.98–72.9 mm BL）from the tidal flat, 239（22.8–107 mm BL）from the wharf using basket nets, 221（6.30–45.2 mm BL）from the wharf using a hand net, two（17.3 and 30.4 mm BL）from the tidal flat using a set net, and one（4.50 mm BL）from the waterway. Based on morphological development, the developmental stages of the larvae and juveniles were divided into four phases each of swimming and feeding functions and five phases of relative growth. The occurrence patterns and ontogenetic intervals imply that hatched larvae are transferred to the sandy beach or tidal flat by flow, occupy these habitats while their swimming and feeding functions develop, then begin migrating to the wharf at 8–9 mm BL. Subsequently, juveniles settle on the seafloor; they then migrate and settle at the wharf until ~35 mm BL. C. gulosus utilizes different habitats in this artificially established seaside zone depending on the developmental phase from hatching to immature individuals, although the distribution of mature individuals remains unclear.

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