Northwest Fisheries Science Center

Instream Monitoring Systems for the Passive Integrated Transponder Tag

Instream Fish Monitoring Systems for the
Passive Integrated Transponder (PIT) Tag

Sandra L. Downing, Earl F. Prentice, Bruce F. Jonasson, and Gabriel T. Brooks

These pages provide an overview of issues relevant to the successful design, installation, and deployment of instream monitoring systems for fish based on the passive integrated transponder (PIT) tag. 

Topics covered here are applicable to either full– or half–duplex PIT systems or to fish telemetry monitoring in general.  These include assessing the biological questions to be answered by the research, evaluation of potential stream–monitoring sites, and managing permission and permit requirements.

Photo of two instream PIT-tag monitoring antenna arrays in the Methow River near Twisp, WA.Two arrays of detection antennas monitor PIT–tagged fish in the Methow River near Twisp, Washington. 

We systematically detail the design considerations for each system component:  the transceiver and instrument box, method of data collection, and power system.  A comprehensive overview of potential antenna designs is provided, along with methods for dealing with electromagnetic interference (EMI).  Finally, we discuss future research and development needs for instream monitoring. 

What is an Instream PIT–tag Monitoring System?

Instream PIT–tag monitoring systems use immersed antennas to record the presence of fish in their natural environment without any further handling or recapture after initial tagging of the fish.  Detection records help researchers to evaluate fish movement, migration timing, growth, and survival. 

These system are composed of a transceiver, one or more antennas, and PIT tags, along with a method of data collection and a power system.  In general, they are divided into two categories based on mode of operation:  full duplex FDX and half–duplex HDX

In either mode, the transceiver is cabled to an external antenna and decodes tag information received by the antenna.  Passive tags do not contain an internal battery, but obtain power inductively from the electromagnetic field generated by the antenna. 

In our examples, we refer mainly to FDX systems because these are the most widely used systems throughout the Pacific Northwest, where the majority of instream monitoring systems are deployed.  Specifically, we reference the FDX-B 134.2-kHz system, whose technologies are based on ISO standards 11784 and 11785

At times, we may also refer to a specific manufacturer.  However, these references are not intended as product endorsements or to inform the reader in making a choice between HDX and FDX systems. 

Who Uses Stream Monitoring Systems?

Fisheries applications for the passive integrated transponder (PIT) tag have been growing since the early 1990s (Prentice et al. 1990a,b,c; Achord et al. 1996; Downing et al. 2001).  In the Columbia and Snake River Basins, PIT–tag data are used extensively to inform management decisions for recovery of endangered salmonids.  Over one million juvenile salmon are PIT-tagged annually in the Columbia and Snake River Basin (Skalski et al. 1998; Muir et al., 2001; Ryan et al. 2003)

A shared database containing tagging and detection records for salmonids throughout the region is maintained by the Pacific States Marine Fisheries Commission (PSMFC 1996).  The PIT Tag Information System for the Columbia River Basin (PTAGIS) is widely used by fisheries researchers and resource managers. 

Inriver PIT-tag detection antenna being deployed off pile dyke in the Columbia river estuary.An array of PIT–tag detection antennas for deployment on a pile dyke in the Columbia river estuary. 

Instream monitoring of PIT–tagged fish is possible in part because of the longer reading range produced by substantial improvements to both the tag and system components.  Other technological advances have reduced the installation and maintenance cost of these systems. 

Today, researchers are using PIT tag technology in streams, small rivers, and sections of larger rivers to monitor fish presence and behavior, evaluate the effectiveness of stock restoration projects, and address various other research objectives (Connolly et al. 2005, 2008; Zydlewski et al. 2006; Wigington et al. 2006; and Horton et al. 2007). 

Our goal is to assist these researchers and their students by sharing the lessons learned during more than two decades of research and development of the PIT–tag and its applications. 


We thank Jim Simonson and Bill Wassard of the Northwest Fisheries Science Center for their help in the design, construction, and installation of of PIT–tag interrogation systems in a number of small streams within the Columbia River Basin. 

Thanks also to Don Warf, Dave Marvin, Darren Chase, and Scott Livingston of the Pacific States Marine Fisheries Commission for providing expertise on remote data transfer and communications. 

Patrick Connolly and Ian Jezorek of the U.S. Geological Survey provided assistance during the deployment and operation of the first stream interrogation system at Rattlesnake Creek. 

Funding for instream monitoring system research and development was provided by the Bonneville Power Administration. 

Finally, we extend posthumous thanks and deep appreciation to Brad Peterson for his work developing the multiplexing transceiver. 

† Reference to trade names does not imply endorsement by the National Marine Fisheries Service, NOAA.