November 1, 2026
A PIT tag is a Passive Integrated Transponder: a small electronic identifier that receives power from a compatible reader and returns its identification code. It has no internal battery. In fish and wildlife work, the transponder is often enclosed in a glass capsule, allowing an individual animal to be identified again over time.
For example, a fish study may need to identify the same fish several months after its first capture. An aquaculture team may need to connect every length and weight measurement to the same individual. Reading that fish’s PIT code again gives the team a consistent reference for its records, making growth or other changes easier to follow over time.
At DO RFID, we supply PIT tags for fish and animal identification. This guide explains the technology so you can distinguish the tag itself from the equipment and data needed around it.
What does “PIT tag” mean?
Passive means that the tag does not use its own battery to transmit. Integrated transponder describes the electronic circuit that responds when interrogated by suitable equipment. A typical glass transponder contains an integrated circuit and a small antenna coil, protected inside the capsule.
PIT technology belongs to the broader family of radio-frequency identification, or RFID. “Microchip” is a common name for an animal identification transponder, while “RFID” describes a much wider range of tags and systems. A warehouse UHF label, an NFC label read by a phone and an animal PIT tag should therefore not be treated as interchangeable products.
Nor does “PIT” describe every possible attachment method. Glass tags may be implanted under an approved animal protocol, while some projects use an externally attached tag. The Smithsonian’s explanation of bird PIT tagging, for example, includes tags carried on leg bands. The identification principle remains the same; the way the tag is carried depends on the application.
How a PIT tag works: from energy to an identification record
A low-frequency PIT reader produces an alternating magnetic field through its antenna. When a suitable tag enters that field, energy couples into the tag’s coil. The electronics can then respond with the tag code. This is why a battery-free tag can still be read, and why a compatible reader must be close enough to establish communication.
1. Reader and antennaCreate the interrogation field
2. Passive tagReceives energy and returns its code
3. Reader outputDisplays or transfers the ID
4. Project recordConnects that ID to observations
Consider a hypothetical hatchery record. At the first measurement, an operator reads the fish’s tag and records its length against that ID. At a later measurement, the same ID is read again. The software can connect the two observations because the identity matches. The tag has not measured the fish’s growth; the measurements were collected separately and associated through the code.
A fixed antenna can perform a different task. Rather than bringing a scanner to an animal, the system records a tag when it moves through the detection area. That event can contain the ID and time, together with the reading location or equipment identity. For a real example of the data structure, PTAGIS interrogation records identify the site, timestamp, tag message and detecting equipment. Other projects may use different software and fields.
The four parts of a useful PIT system
| Part | What it does | What to decide |
|---|---|---|
| Tag | Provides the electronic identity | Size, supported protocol, encoded format and packaging |
| Reader | Powers and decodes compatible tags | Handheld or fixed operation, supported formats, display and data output |
| Antenna | Creates the useful interrogation area | Geometry, position, installation environment and intended tag path |
| Records | Connect the identity to observations | How IDs, measurements, events and corrections will be stored |
A handheld device often combines the reader and antenna in one housing. A fixed installation may have a separate reader, antenna, power supply and logging equipment. Knowing this distinction prevents an expensive mismatch: a pocket scanner can be useful for checking a tag in hand without being a substitute for an unattended stream-monitoring station.
What are PIT tags used for?
Fish identification and repeated measurements
In a fish project, a stable ID lets staff associate measurements or observations with the same individual. Possible records include length, weight, stock group, treatment or breeding information. The value comes from maintaining the relationship between the tag code and the fish’s record, rather than trying to recognize the individual by appearance alone.
Movement through known reading points
Antennas at suitable locations can record passage events without requiring a manual scan on every occasion. Researchers can relate those events to the questions their study was designed to answer. Detection coverage still matters: an animal outside the reading area has not been located simply because it carries a tag.
Wildlife and managed-animal observations
A reader at a feeder, nest entrance or other predictable access point can connect an individual identity with a visit. During manual examinations, a scanner can connect the animal with its existing record. These are different workflows, and the equipment should be chosen around the intended observation.
For a fuller explanation of how fish observations become study data, see our fish PIT monitoring guide.
What information does the tag contain?
For basic identification, the essential output is the tag code. The animal’s name, weight history, study group or owner details are normally held in an external record. A scanner reading an ID does not automatically retrieve every piece of information about that animal: the record must exist, the ID must match, and the operator must have access to the relevant system.
Some transponders support configurable memory or sensing functions. Those features belong to particular chips and implementations. They should not be inferred from the words “PIT tag” alone. Likewise, a reader that supports ordinary identification is not automatically able to obtain temperature from every chip.
What PIT tags can and cannot do
The absence of a battery is a practical advantage for long-term identity: the tag does not need routine battery replacement. Compact construction also allows projects to consider animals and life stages that would be difficult to equip with a larger powered transmitter.
However, the reader must be able to detect the tag. A PIT tag does not independently send its position to a phone or satellite. An event recorded at one antenna tells you that the code was detected there at that time; it does not reveal every movement between antennas.
“Long-lasting” also has several meanings. The electronics may remain functional while the animal leaves the monitored area. An observation can be missed even though the tag is present. An old tag may be readable while the associated record has been lost. Our PIT tag lifespan and retention guide separates those questions.
Are PIT tags and readers all compatible?
No. Frequency is only one part of compatibility. The tag’s communication format and encoded data must match what the reader supports. Low-frequency animal systems can use FDX-B or HDX, and readers may support one format or both. A shared nominal frequency is not enough to establish that a particular pair will work.
Start with the exact tags and infrastructure already used in the project. If the project will share detections with another program, that program’s requirements also matter. Selecting equipment around an established detection network is a different decision from choosing a small, self-contained system for manual identification.
The practical reading distance is equally specific to the combination. For the difference between a close-range scan and a fixed detection area, read our PIT tag read-range guide.
DO RFID PIT tag sizes and product options
Our individual glass transponder range includes the following six capsule sizes. G-001 through G-006 use EM4305 with 134.2 kHz FDX-B identification. The table provides a starting shortlist; the project’s animal size, tagging procedure and reading equipment determine which option is suitable.
| Product option | Capsule diameter × length | Needs to discuss |
|---|---|---|
| G-001 · 7 mm FDX-B PIT tag | Ø1.25 × 7 mm | Small-fish studies or projects evaluating a very compact capsule where implantation space is limited |
| G-002 · 8 mm FDX-B PIT tag | Ø1.4 × 8 mm | Juvenile-fish or small laboratory-animal projects assessing compact identification tags |
| G-003 · 12 mm FDX-B PIT tag | Ø2.12 × 12 mm | Routine individual-animal identification where the project can accommodate a 12 mm capsule |
| G-004 · 13 mm FDX-B PIT tag | Ø3 × 13 mm | Projects comparing a 3 mm diameter capsule with the narrower 12 mm option |
| G-005 · 15 mm FDX-B PIT tag | Ø3 × 15 mm | Projects specifying a 15 mm capsule; this size is also available in a preloaded injector configuration |
| G-006 · 32 mm FDX-B PIT tag | Ø4 × 32 mm | Projects whose animals and tagging procedure can accommodate the largest capsule in this range |
| G-007 · Temperature-sensing glass tag | Ø2.12 × 12 mm | Animal ID plus tag-measured temperature, using a reader that supports EL9265 temperature data |
Length alone does not define a tag: the 12 mm and 13 mm options above also differ in diameter. A smaller capsule should be evaluated with the intended reader and handling method. Our PIT tag size guide for fish explains those tradeoffs.
Loose glass tags or preloaded injector sets?
- Individual glass tags: G-001 through G-006 are supplied without injectors, in bags of 100 tags. This format suits projects that already have appropriate implantation equipment and a defined preparation procedure.
- Preloaded injector sets: options include Ø1.4 × 8 mm tags in G-101 or G-103, Ø2.12 × 12 mm tags in G-102, G-106 or G-107, and Ø3 × 15 mm tags in G-105. Each set contains one tag in a single-use injector, a barcode sticker and individual paper/plastic packaging. Injector designs differ between models.
G-105 offers either an EM4305 FDX-B or SIC7999 HDX configuration at 134.2 kHz. Specify the required version when ordering; the two formats are separate choices. An injector set supplies the tag and applicator, while a complete project kit may also need reading equipment, recording tools and other consumables.
Three practical ways to choose and buy a PIT configuration
1. You already have a reader and need compatible tags
Confirm first: the reader’s exact model, supported protocol, expected ID format and the tag dimensions used in the project. If detections must enter an established network or database, include its tag-code requirements.
What to order: replacement tags in the matching configuration, supplied loose for an existing applicator or preloaded when a new injector is needed. For an FDX-B system, the G-001–G-006 range gives six capsule sizes to assess. For an HDX requirement, the G-105 SIC7999 option is a different configuration to evaluate.
The project’s part: check sample tags with the actual reader before a larger order, verify that IDs reach the records correctly, and confirm that the selected capsule and applicator fit the approved tagging procedure.
2. You are starting your first PIT tagging project
Confirm first: which animals will be identified, their size or life stage, whether scans will happen during handling, and how staff will record each observation.
What to order: a suitable tag configuration, a compatible reader and an implantation tool. Preloaded G-101/G-103, G-102/G-106/G-107 or G-105 sets combine tags with injectors; choose the reader separately for the selected protocol and required data output.
The project’s part: arrange animal-care approval and trained operators, prepare records and consumables, and test the complete scan-to-record workflow. Our PIT reader selection guide covers equipment choices, while the project cost guide helps budget beyond the tags.
3. You need a fixed antenna for fish-passage monitoring
Confirm first: the channel dimensions, intended detection area, existing network protocol, site power and how detection events will be collected. Define whether the study needs a passage record at one point or a sequence of detections across several locations.
What to specify and buy: compatible tags plus a fixed reader, antenna, suitable power supply and data-logging arrangement. Select tags against the system specification. A handheld scanner can help check tags, but the fixed installation needs equipment designed for its detection area.
The project’s part: have the project team or system integrator design and install the antenna arrangement, assess site noise and water conditions, test detection performance, and maintain the records. Buying tags or preloaded injectors alone does not provide that installation.
Explore DO RFID PIT tags for your project
Ready to compare supply options? Visit our PIT tags for fish and animal identification page. Use the size and packaging choices above to prepare your enquiry: include the proposed model or capsule dimensions, reader model or required protocol, quantity, and whether you need individual tags or preloaded injector sets.
Frequently asked questions
Does a PIT tag need a battery?
No. A passive PIT tag receives operating energy from the compatible reader’s field.
Can a phone read an animal PIT tag?
A phone’s built-in NFC function does not replace the compatible low-frequency reader used for typical animal PIT tags. A phone can participate through supported external reading equipment and software.
Can a PIT tag track an animal anywhere?
It provides an identity when detected by suitable equipment. Locations between detections are not automatically recorded by the tag.
Is 12 mm the only PIT tag size?
No. Multiple lengths and diameters are used. The appropriate configuration depends on the animal, study, reading equipment and other project conditions.
Does reading an ID prove that the animal is alive?
The detection proves that a tag code was read. Interpreting that event as an observation of a live animal requires the study context and any supporting evidence.
Do RFID is a leading China-based manufacturer with over 15 years of experience. We specialize in customized RFID readers, tags, and cards, delivering high-quality, tailored solutions that meet your unique business needs and drive seamless, efficient identification.
