The VIE tagging method depends upon implanting material beneath transparent or translucent tissue. The fluorescent elastomer material is injected as a liquid that soon cures into a pliable, bio-compatible solid. Tests conducted by NMT and others have clearly demonstrated that VI Alpha shedding is exacerbated with decreasing fish size and by relative stiffness of the tag. The contrasting texture of VIE, the small volume of material required, its tendency to occupy available space rather than displace and irritate surrounding tissue, combine to make VIE more useful in smaller specimens. This enabled Frederick (in press) to mark reef fishes as small as 8 mm standard length.
The VIE colors facilitate visibility under normal lighting conditions and provide the option of greatly enhancing visibility under ultra-violet light or with other fluorescence enhancing techniques (see figure 3). This feature was used to advantage by Buckley, et al. (1994) in recovering small tagged reef fishes using ultra-violet underwater lights; and similarly, by Bonneau, et al. (1995) in enumerating tagged trout in streams.
Four colors (red, yellow, green, and orange) constitute the only intrinsic VIE codes. If only one mark per fish were used, the number of potential unique marks is simply the product of the numbers of colors used and the locations. However, if two marks are used in each specimen, in combination with several different locations, a surprising number of unique codes can be devised. The following formula relates to determining the number of unique codes that can be devised utilizing two marks per individual:
Number of Unique Codes = L x (L - 1) x C x (C - 1/2)
Where C = no. of colors used, and L = no. of body locations. For example, six body locations used with four colors, would provide: 6 x 5 x 4 x 3 1/2= 420 unique codes.
Figure 4: Elastomer tagging a coho salmon using the hand injection method
Advantages of the VIE tags: