Aspect of reproductive ecology of Caridina typus and Caridina sakishimensis were studied in six headwater streams in Kikai-jima Island, Southern Japan. Monthly surveys were conducted from June 2005 to June 2008. Shrimp specimens were collected with a hand scoop net. The population size of C. typus was lowest during high precipitation periods but showed immediate recovery attributed to successful recruitment and increased following the major spawning activities, while that of C. sakishimensis remained stable throughout the study period. The breeding season of C. sakishimensis was estimated to extend from March to November, with a main breeding season lasting from June to September, while that of C. typus lasted from March to December. Overall ovigerous females comprised 50% to 80% of mature females of C. sakishimensis during the main spawning season, which indicated that this species remained and spawned mainly in the headwaters. Both C. sakishimesis and C. typus carried a large number of small sized eggs. This study revealed that the spawning season, egg size, and brood size are similar in both species; usage of headwater streams was different between C. sakishimensis and C. typus. Caridina sakishimensis employed these water bodies as spawning ground while C. typus used them as nursery ground.
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Vol. 31 • No. 1