Ovarian maturation, size at sexual maturity, and spawning season of jack-knife shrimp Haliporoides sibogae (Decapoda: Solenoceridae) in Kagoshima Bay, southern Japan

Jack-knife shrimp Haliporoides sibogae is a target species for boat seine fishery in the waters off south-western Kyushu, Japan. Reproduction, including ovarian maturation, size at sexual maturity, and spawning season of this species were studied using females collected from Kagoshima Bay, southern Japan. The present study also explored an alternative maturity index by conducting a microscopic examination of oocytes. Histological analysis of the ovaries validated six oocyte developmental stages. Ovarian development was asynchronous, indicating multiple spawning throughout a reproductive season. On the basis of the developmental stage of the most advanced oocytes, ovarian maturity was categorized into three stages: immature, maturing and mature. Females containing oocytes exhibiting cortical crypts were defined as mature. The gonadosomatic index (GSI) significantly increased as ovarian maturation progressed, and all females with a GSI of ≥ 6% were determined to be mature. The minimum size at sexual maturity was estimated to be 24.0 mm in carapace length. The spawning season extended from November to May, with February being the peak. Moreover, microscopically, the oocytes with spherical bodies on the periphery all had cortical crypts. Therefore, observation of oocytes using a microscope was considered an effective method to easily identify mature females.