UNPALATABILITY OF A COLONIAL ROTIFER, SINANTHERINA-SOCIALIS TO SMALL ZOOPLANKTIVOROUS FISHES

Colonies of Sinantherina socialis (phylum Rotifera) form conspicuous m asses that should make them extremely vulnerable to fishes capable of ingesting small live prey (<3 mm in length). To test this hypothesis w e offered rotifer colonies as prey to 14 species of small-mouthed, pre datory fishes, alternating with small cladocerans. Most rotifer coloni es (71-100%), but few cladocerans (0-14%) were rejected after capture. Fish feeding behavior on rotifers followed a consistent pattern: loca te, approach, attack, mouth repeatedly, and reject (spit out). Except for loss of a few individuals, rotifer colonies that had been repeated ly rejected remained undamaged. This is the first evidence for unpalat ability of rotifers to zooplanktivorous fishes.