Temperature impacts on reproductive parameters for Japanese anchovy: Comparison between inshore and offshore waters

Batch fecundity and spawning frequency data for Japanese anchovy Engraulis japonicus, as well as sea surface temperature (SST) data, derived from the recent literature, were compared between inshore samples (Sagami Bay) and offshore samples (western North Pacific) of anchovy. The offshore anchovy were heavier in body weight and had heavier ovaries than the same-size inshore anchovy. Relative batch fecundity was positively related with gonadosomatic index (GSI) and SST for both the inshore and offshore anchovy; however, the relationships with GSI and SST differed between these two groups. The relative batch fecundity of the inshore anchovy rapidly decreased as SST decreased, while that of the offshore anchovy decreased rather gradually. Although the level of spawning frequency seemed similar between the two groups, the positive relationships to sea temperature differed: the offshore anchovy would spawn at temperatures ca. 5 °C lower as frequently as would the inshore anchovy. Comparison of temperature impacts on reproductive parameters suggested the existence of differences between the inshore and offshore anchovy in their specific spawning ecology.