An esophageal implant transmitter with a trailing antenna is implanted into the stomach using an esophageal insertion tube. The antenna exits the fish from the corner of its mouth. This method is primarily used on salmon that enter fresh water to spawn and no longer ingest food. This attachment minimizes changes in the behavior of the fish. Good field range is obtained through the trailing whip antenna, and even better range will be realized if the enhanced range option (models with "B" suffix) is chosen.

Series	Weight (grams)	Life (days)	Description
F1405	.50-.85	20-51	Smallest sizes, reduced power output for longer life, minimum potting for lowest weight., silver oxide battery, cylindrical shape. Limited frequency availability.
F1400	1.0-2.1	7-83	Small size, standard power output for normal life, normal potting for durability, silver oxide battery, cylindrical shape.
F1700	1.4-3.4	2-37	Small size, cylindrical shape, stacked silver oxide batteries (2).
F1800	2.5-130.0	10-1095	Medium to larger sized, cylindrical shape, lithium battery. Enhanced range option available.