Faculty of Fisheries, Kagoshima University, Kagoshima 890-0056, Japan
The timing of mating related to ovarian maturation was examined for a natural population of the open-thelycum penaeoid shrimp Solenocera melantho. Inseminated females were found only during the spawning season with its peak in October. Judging from the histological observations of ovaries of the inseminated females, males mated with females having prematuration-stage oocytes with cortical crypts in the peripheral part of the cytoplasm. The attached spermatophore came off from the open-thelycum shortly after spawning. Percentage occurrence of inseminated females increased from 06：00 until 12：00. All inseminated females collected before noon had prematuration-stage oocytes, whereas, in the afternoon most of the inseminated females had maturation-stage oocytes. In S. melantho, mating occurred during the period between immediately before the sunrise and noon, then the mated females spawned before the sunrise of the following day.