Fish can generally continue to feed after the tags are inserted into the stomach according to some studies.  These devices can be expelled via regurgitation (vomiting) or egestion (defecation).  The expulsion rate depends on the species of fish and the device size relative to the size of the fish.  In general, larger tags are more likely to be regurgitated whereas smaller tags are more likely to be defecated.  The coating and/or shape of the device may also influence retention.  Some researchers place rubber bands or surgical tubing rings around the transmitter package to increase the “roughness” and reduce regurgitation.  It is always a good idea to assess the retention rates of devices that will be used by conducting preliminary laboratory studies prior to launching a large scale field study.  Retention rates can be affected by the stress in fish resulting from the capture method.  It is therefore important to minimize capture and handling stress.

This tagging method is probably the least invasive, in terms of handling and injury to the fish, when it is done properly.  Tagging induced mortality is quite low for this procedure.  The plungers used are tube-like structures (usually a tube within a tube) that are smooth and sometimes lubricated to aid in the insertion.  It is possible to insert a transmitter with an antenna without having to use an actual plunging device.  The antennas either trail out of the mouth, and bent to be positioned alongside the fish, or they exit through the operculum.  The antennas are sometimes sutured to the roof of the mouth or to the wall of the body.  This minimizes the abrasion and subsequent infections in the corner of the mouth or along the gill arch as a result of antenna movement.

Transmitters can be ingested voluntarily when they are embedded or wrapped in bait.  When this happens, data collection can be commenced immediately since there is no time spent for handling and tagging.  In addition, transmitter retention rates may be higher when the transmitters are ingested voluntarily as compared to those when transmitters are inserted manually.