The methods of juvenile production of Udang Galah (Macrobrachium rosenbergii) have been documented by several workers (Ling, 1969; Ling and Costello, 1976; Fujimura 1966, 1967', 1968, 1972; Fujimura and Okamoto, 1970; Sandifer et al., 1976). The methods given by these workers involve intensive hatchery management such as frequent water change and cleaning of larval tanks to ensure good sanitation. Such a technique would involve wastage of seawater and at the same time is labour intensive. To overcome the above mentioned problems a study was conducted at the hatchery of the Faculty of Fisheries and Marine Science, Serdang} to produce “Udang Galah” juveniles without water change and by using “green water3 at salinities 6-8°foo and 12-14° joo respectively. Previous studies by Cohen et al. (1976) have conclusively shown that ‘green water3 is an efficient system to remove toxic metabolites such as ammonia from the culture medium. The ‘green water3 which mainly consists of unicellular algae such as Chlorella is produced by exposing water of salinity 6°loo which contained Sarotherodon mossambicus to sunlight (Fujimura, 1966).