The digestive efficiency of the chaetognath Sagittacrassa Tokioka, with observations on the feeding process

The chaetognath Sagitta crassa Tokioka, which is abundant in Tokyo Bay, may seize and ingest several copepods within the space of a few minutes under laboratory and natural conditions. This chaetognath consumed about a third of its daily ration within 2 h after receiving a supply of food. After partial ingestion of a copepod, S. crassa occasionally relinquished its prey, which was immobile and appeared to be paralyzed. Large numbers of bacteria were found on the exoskeleton of a released copepod, instead of the expected holes from piercing by chaetognath teeth. S. crassa had a mean digestion time of 2.2 and 2.8 h for Acartia clausi Giesbrecht and Tigriopus japonicus Mori, respectively. The digestive efficiency of Sagitta crassa was determined gravimetrically and it ranged from 56 to 93%, depending on the food items, with a mean of 83%.