The rotifer, Brachionus rotundformis along with a smaller strain were isolated for the first time from Cochin backwater. The newly isolated B, rotundformis has a length range of 98-210 microns showing a modal size of 168 microns, while in the smaller strain the length ranged from
70-168 microns with modal size at 140 microns. The lorica width to length ratio for B. rotundiformis is 0.7 and that for smaller strain 0.8. The smaller strains are of much use for feeding fish larvae especially those having small mouth size
