Hallprint's range of body cavity internal external anchor tags (type IEX) provide the researcher with an option that is really worth contemplating if extremely long term tag retention is desired, such as for population size or exploitation rate estimates. These tags, developed by Michael Hall and Dr Mark Mattson in the early 1990s, have now been successfully applied to a number of freshwater and saltwater fish and show excellent tag retention properties while having minimal apparent impact on fish behaviour and condition.
IEX tags provided an excellent internal anchor in the abdomen while requiring only a needle prick in the body cavity wall to accommodate the tag. The tag is designed such that the anchor lies parallel with the inside abdomen wall and the external marker lays backwards along the line of the fish.
The IEX tag may take a longer time to apply than the T-bar or dart tags, are more expensive and may be less suitable for high volume tagging operations, especially when holding time is critical. It is favoured by some researchers tagging finfish species for the following reasons -
- Tag retention appears to be excellent in most species;
- Algal growth on the tag may be reduced through the ventral positioning of the tag which reduces light exposure levels; and
- There is usually minimal damage to edible muscle tissue.