Radio tagged juvenile coho salmon 120 days post surgery. (USFWS photo: G. Stutzer)

Gross anatomy internal view juvenile coho salmon wth radio transmitter 120 days following surgery. (USFWS photo: G. Stutzer)

Gross histology of tissue encapsulating a radio transmitter 120 days post surgery. (USFWS photo: G. Stutzer)

by Gregory Stutzer, Arcata FWO
Biologists examined the effects of surgically implanted radio transmitters on survival, growth, and tissue response of 100 Trinity River Hatchery juvenile coho salmon Oncorhynchus kisutch (126-203 mm fork length) to measure negative effects and determine if long-term retention of transmitters occurred.  Transmitters represented between 0.8 – 2.5 % of test fish body weight.  Growth did not differ significantly between control and surgery groups having radio transmitters surgically implanted over a 120-d study period.  An unexpectedly high number of both control (12) and surgery (21) fish died during the experiment.  Post-mortem workup of these fish by the California Nevada Fish Health Center revealed a high level of infection of Renibacterium salmoninarum, the causative agent for bacterial kidney disease (BKD).  No fish lost transmitters during the course of the study.  All transmitters retained by fish were completely encapsulated in a dense layer of connective tissue by day 120.  With proper surgical procedure, intraperitoneal implantation provides a suitable method for long-term attatchment of radio transmitters for biotelemetry studies of juvenile coho salmon greater than 126 mm fork length.  However disease prevalance should be determined prior to performing studies of survival in natural systems.