Visible Implant Elastomer (VIE) Tags are colored fish tags. They are also used to tag crustaceans, cephalopods, gastropods, reptiles, amphibians, small mammals, arachnids, and other animals. The elastomer is injected as a liquid that cures into a pliable solid. The tags are implanted beneath clear or translucent tissue and remain externally visible. Visible Implant Elastomer tags are small, flexible, and bio-compatible. This makes them useful for a wide variety of species (click here for some examples) and in animals smaller than most other tags can accommodate.
Visible Implant Elastomer comes in 10 colors. Red, pink, yellow, green, orange and blue are fluorescent. Black, purple, brown, and white are not. The fluorescent colors are highly visible in ambient light and provide the option of greatly enhanced tag detection when fluoresced with the VI Light. Fluorescing the tags is especially helpful when tagging under pigmentation or when recovering tags in the dark. This video about tagging glass eels to evaluate dam passage shows how effective the fluorescence can be.
VIE color selection can be tricky and getting it right is an important part of your experimental design. Your choice depends on how much contrast you need with the background pigmentation, how many different colors you require, and the type of light you will use to fluoresce the tags.
- Exhaust all possibilities with fluorescent colors before using non-fluorescent colors. Maximum tag detection is obtained by fluorescing tags with the VI Light.
- Use non-fluorescent colors only when there is no potential for the tag to become obscured and when all tag detection will occur in bright light.
- When using the VI Light, we recommend that the first four colors selected be red, yellow, orange, and blue.
- Test the product under field conditions before beginning large-scale projects.
Colors that may be confused when using the VI Light:
- Green and yellow appear nearly identical.
- Red and pink look similar but can be separated if the VIE Color Standard is used and if the samplers are trained. We recommend that you test these two colors in your animal and with the samplers who will recover the tags.
Colors that may be confused in Ambient Light:
- Black and brown appear nearly identical.
- Brown and purple look similar. With the VI Light, purple will appear much lighter while brown does not change. This feature may be used to help distinguish these colors.
Generate a Coding Scheme
While VIE is primarily used for batch identification, you can generate a VIE coding scheme by combining multiple tags, tag locations, and colors. For example, researchers tracking seahorses used this method to distinguish more than 500 individual seahorses at one time.
Six fluorescent colors (red, yellow, blue, orange, green, and pink) and four non-fluorescent colors (black, brown, white, and purple) constitute the only intrinsic VIE codes. If you use just one tag per fish, the number of unique codes is simply the product of the numbers of colors used and the number of tag locations.
However, if you inject two or more tags in each animal, in combination with several different locations and colors, you can generate an extensive VIE coding scheme. In any tagging program, it is important that all of the study animals have the same number of tags. That way, there can be no confusion between animals which lost tags and those which began with fewer tags.
How many codes?
Calculate the number of unique codes you could create using the formula:
Where: C= Number of colors used, L= Number of body locations and N = Number of tags per animal.
For example, three body locations used with four colors (C = 4, L = 3, N = 3) would provide: (3!/0!3!)43 = 64 unique codes. Recall that 0!=1.
There’s an app for this! NMT’s VIE Color Code Generator quickly calculates and lists the unique codes available for a given combination of body locations, tags and colors. You can download a free copy.
If you are tagging reptiles or amphibians, you may also like to check out Salamarker – another VIE code generator created at Purdue University.
VIE Tag Detection
A powerful feature of Visible Implant Elastomer tags is that red, pink, yellow, blue, orange, and green can be fluoresced for enhanced detection. When fluoresced, a small spot of VIE can be seen at considerable distance and in the dark, and tags obscured by pigmentation are often detectable. However, color perception can vary among samplers. Tags of different colors can generally be distinguished in ambient light in clear tissue, but those same colors may be confused if the marks are poor or are placed under pigmented tissue. Fluorescing the tags greatly enhances tag detection, but red and pink, and green and yellow, look similar when fluoresced.
Maximize Tag Identification
- Choose distinct colors for tagging.
- Tag in clear tissue whenever possible.
- Train your samplers – let them practice with the tag colors they will encounter before they start collecting data.
- Use the VIE Color Standard to correctly identify colors.
- Use the VI Light to fluoresce poor or obscure tags.
VIE Color Standard
NMT’s VIE Color Standard presents the ten VIE colors on a clear card. This allows the sampler to place the color sample directly beside a tag for comparison, either under or over the tagged tissue.
Customized color standards can be made at the time of tagging by dispensing some tags onto clear stiff plastic and then covering them with clear packing tape after the marks have cured. Labeling the colors is helpful.
Test the VI Light with the VIE Color Standard to ensure that the tags are adequately fluoresced. Shine the light directly on the area where the tag is thought to be. If you are working in direct sunlight, you will need to fluoresce the tags in the shade – even the shade of your body is probably enough. Very faint tags are best seen when fluoresced in darkness.
CAUTION! Our VI Lights are very bright, but you can hardly see their light. They do not trigger the eye’s normal defense mechanisms against bright light. Never stare directly into any light used for fluorescing VIE tags, and keep these lights out of the reach of children.
For manual tagging, VIE is sold in kits suited for all sizes of projects. The kits are easily transported into the field. Very large projects may benefit from using our Air Driven Elastomer Injection System.
We can help you decide whether VIE is suitable for your species, provide you with relevant publications, suggest which colors may work well for you, help you choose the best tagging locations, and estimate how much elastomer you will need. Please contact NMT with any questions.