Alaboratory study was carried out to examine the effectiveness of juvenile freshwater prawn, Macrobrachium rosenbergii (De Man, 1879), as a planktonic crustacean predator.
The results showed that large juvenile prawns (body length 4.5-4.8 cm) ingested significantly more zooplankton than did smaller ones (1.1-1.5 c,) when zooplankton density was 5.3 prey /ml . The large juvenile specimens consumed 2705 zooplankton on average, after 12 h, while the medium sized prawn (3-3.5 cm, body length) , medium small (2.1-2.4 cm) and small (1.1-1.5 cm,) size groups ingested 1570, 1440 and 1258 zooplankton respectively. Large prawn consumed prey of larger body size than did smaller prawn .More zooplankton were consumed by the prawn when the zooplankton density was high (8.45-9.8 prey/ml.). The clearing rate (no of zooplankton ingested /no. of zooplankton offered) was, however, lower (69%) when the zooplankton density was high. The results indicate that juvenile M. rosenbergii can effectively ingest zooplankton which play an essential role in the food web of the prawn.