抄録
Freshwater shrimp, Macrobrachium nipponense, were collected in summer from an artificial brackish-water lake, Lake Koj ima, in Okayama Prefecture, western Japan. Their hatched larvae were reared in the laboratory at 25°C in different salinities ranging from 0 to 32 ‰. The pelagic larvae successfully metamorphosed to the 1st postlarva only in salinities of 4 and 16 ‰ with survival ratios of 15 to 20 %. In the laboratory, an increase in salinity from 4 to 16 ‰ accelerated the settlement of middle-stage pelagic larvae. This, however, resulted in a shorter larval period and smaller 1st postlarvae than those obtained in 4 ‰. A field survey in late summer showed an aggregation of 7th-to 9th-stage zoeae and 1st post larvae in more saline (1-20 ‰) deep water, while 1st- to 3rd-stage zoeae were distributed in the less saline (0-1 ‰) surface water. Thus, both the laboratory experiment and field observation indicate that high salinity water induces larval settlement of M. nipponense in this brackish-water lake.
