Abstract
The spawning characteristics of the konoshiro gizzard shad Konosirus punctatus in Tokyo and Sagami Bays, including spawning grounds, periods, water temperature and salinity, and relationship of egg distribution with environmental conditions were studied. Shifts in the main spawning grounds and environmental changes in water temperature and salinity during spawning in each bay were observed. It was found that: (i) the spawning period in both bays was from April to July; (ii) the main spawning peak periods and grounds were May in outer Tokyo Bay, June to July in inner Tokyo Bay, and April in Sagami Bay, off Hayama; (iii) spawning grounds in Tokyo Bay dispersed northward from the outer to the inner bay after May, and in Sagami Bay, westward from Hayama after April; (iv) these shifts correlated with environmental changes, from colder to warmer temperature, from higher to lower salinity, and from heavier to lighter specific gravity; (v) water temperature and salinity for major spawning ranged from 16 to 19°C and 31.5-34.5 p. s. u. with resulting specific gravity of 23.0-25.0 kg/m3. The spawning grounds and periods of this species appeared to be decided by definite spawning temperature and salinity, which are fundamental ecological factors.
