HOW THE GRASS CARP(CTENOPHARYNGODON-IDELLA) CHOOSES AND CHEWS ITS FOOD - SOME CLUES

Grass carp were allowed to feed on a variety of plants, presented one species at a time. They were filmed and their faeces collected. Canadian pondweed, a grass and a filamentous alga were readily taken; greater duckweed, shining pondweed and the leaves of reedmace were not so acceptable. Limiting factors in feeding seem to vary: with the two pondweeds foraging is limiting, probably because the leaves make it difficult for the fish to extract a single, manageable stem. Transport is limiting with the grass-the fish cannot swallow it quickly enough. Chewing is limiting with reedmace leaves (they are too tough) and the filamentous alga (for no apparent reason). Duckweed is rejected, probably because it has an unpleasant taste. All plants are chewed at the same frequency of jaw movement, independent of the texture of the plant.