Growth and reproductive characteristics of yellowtail, Seriola quinqueradiata, collected off western Kyushu from February 2003 to April 2007 were determined based on vertebral centrum readings and gonad histology. The formation pattern on the centrum surface was distinct, and opaque zones (annuli) were visible. There is no significant difference in the von Bertalanffy growth parameters between males and females, and the combined growth model was FL_t=1042 [1-exp {-0.311 (t+0.988)}], where FL_t is the fork length (mm) at age t (years). The spawning period was estimated from March to May in the study area based on the results from monthly changes in the gonadosomatic index and maturity stage composition. Maturation body size (FL) and age were estimated to be 605 and 632 mm for male and female, respectively, and 2 years old for both sexes.

Primary productivity in the Shitaba Bay of Uwa Sea was measured by the in situ ¹³C tracer method one to three times a month for three years from February 2002 to January 2005, together with the hydrographic observation and chlorophyll a and nutrients analysis. The depth-integrated primary productivity ranged from 0.11 gCm^-2 day^-1 to 1.83 gCm^-2 day^-1 during the observation, and the annual primary productivity was estimated to be about 193 gCm^-2 year^-1. The productivity was highest in summer (0.82 gCm^-2 day^-1) throughout the year, followed by that of autumn (0.68 gCm^-2 day^-1), spring (0.44 gCm^-2 day^-1), and was lowest in winter (0.18 gCm^-2 day^-1). There was a correlation (r=0.77, p<0.01) between the primary productivity and depth-integrated chlorophyll a (mgm^-2) throughout the year, and high correlation (r=0.96, p<0.01) was found in autumn but no correlation was found in summer. The chlorophyll a specific productivity generally tend to increase with the surface irradiance, but in summer the chlorophyll a specific productivity was considerably variable, probably due to the different nutrient availability. High chlorophyll a specific productivity may be linked to the intrusion of bottom water, which may play an important role in supporting the biological productivity of Shitaba Bay.

In order to reveal vertical distribution patterns of two mysid species, Neomysis, we collected the mysids from surface, middle and bottom layers in Hiroura Lagoon located in the estuary of Natori River, twice in spring and neap tides, 1994. N. awatschensis and N. japonica coexisted in the lagoon. Although both species distributed mainly in the bottom layer, they occurred in the surface and middle layers in night time. Through correlation analysis, negative effect of illuminance on the density of mysids was found. Their distributions would be expanded to the surface due to their swimming activities enhanced in night. Relationship of stomach fullness and maturational condition with the diel vertical distribution of N. japonica was not significant; however, juvenile N. awatschensis and the mysid without full stomach contents tended to distribute in the middle and surface layers. N. japonica often disappeared from the bottom layer, while N. awatschensis stayed there almost all the time. Behavioral differences were shown between these species.