Scientists have been tagging individual whitebait in an effort to re-introduce the disappearing species to Auckland waterways.
Thirty giant kokopu, which in their juvenile form are one of the five Galaxid species which comprise whitebait, have been released into a stream at Orewa, just north of Auckland.
It's thought the fish were once common in Nukumea Stream but none have been seen since 2002.
The three-year-old fish were bred from eggs and mini tags to trace them inserted in October.
A culvert has removed to restore access from to the sea, and antennae placed at the top and bottom of the stream monitor their movements and what habitats they prefer.
If they do well, between 500 and 1000 will be released at a later date.