Shimonoseki University of Fisheries, Shimonoseki, Yamaguchi 759-65, and, 1Faculty of Agriculture, Kyushu University, Higashi-ku, Fukuoka 812, Japan
The Japanese atyid shrimp, Caridina japonica De Man, spawns small eggs, measuring 0.50×0.31 mm at spawning. The larvae show optimum growth under rearing conditions of 16.9‰ salinity, 25°C water temperature and by feeding an artificial diet, used in fish aquaculture, mixed with a small amount of rice bran. The hatched larvae develop to juveniles through nine zoeal stages, without a megalopa, over about one month. Zoeal stages and the first juvenile are described and illustrated in detail; these are compared, morphologically and ecologically in some important characters, with those of several atyids reported previously. The present species shows the typical larval development of the group of atyids characterized by small eggs. Like C. weberi, the number of zoeal stages is nine, which is larger than that for other members of the same genus and smaller than that for Atya innocous and Micratya poeyi. The stalked eye appears in the second zoeal stage as in almost all atyids bearing small or medium sized eggs. The first pereopod is completed morphologically in the third stage and all pereopods in the seventh stage. The pleopods are first recognized as buds in the sixth stage and the uropod is completed in the fourth stage.