POPULATION ECOLOGY OF NEOCARIDINA DENTICULATA(DE HAAN, 1849) (CARIDEA, DECAPODA) IN THE SUGOW RIVER, JAPAN

Abstract

Three types of the life cycle of the atyid shrimp Neocaridina denticulata were observed in the Sugow River, Japan. A short generation cohort (type I) showed high growth at the high water temperatures occurring after hatching in early June ; many ovigerous females were observed subsequently in early and middle August and they died. A long generation cohort (type II) hatched in mid July and large females incubated eggs during late August and late September but they grew little at low water temperature from November to the following March and ovigerous females appeared again in May. Hatching of another long generation cohort (type III) occurred in late August ; growth recommenced after the months which of low water temperature ; and females incubated eggs during early June and early August. The population were consisted of two groups which took the same cyclic change of generation types, I→III→II→I→III→II→I→(continued), with time lag of a year each other. Growth equations over the life cycle for types I→III, including seasonal variation, ate described. The influence of mest size selection, by sweep nets, on sample size frequency distributions in also discussed.