Abstract Some areas of the spawning and nursery grounds of Japanese anchovy ( Engraulis japonicus ) and Japanese sardine ( Sardinops melanostictus ) overlap both spatially and temporally. The sardine's spawning ground overlap ratio is greater than that of the anchovy. Many sardine larvae inevitably share their habitat with anchovy larvae. However, the interspecific interaction is found only from sardine to anchovy. The focus was on overlapping suitable nursery grounds to explain this unidirectional interspecific interaction. Suitable nursery grounds are defined as the areas where larvae grow faster. If an area with both anchovy and sardine has a specific environmental condition suitable only for sardine growth, sardine will survive there more easily than the anchovy. Suitable conditions based on growth rates were obtained from a combination of otolith analyses and backward particle tracking experiments were estimated. The sizes of suitable areas for each species and both species were estimated considering the ideal conditions for both species. The overlap ratio for suitable anchovy nursery grounds was higher than for sardine during the overlapping spawning period. Based on these results, the following hypotheses were proposed. Although anchovy and sardine larvae occur in the same area, the area is often suitable only for sardine larvae growth. Rapid growth works advantageously regarding interspecific competition as long as food resources are limited. This hypothesis can explain the one‐way interspecific interaction from sardine to anchovy.