A small but mighty freshwater fish
Words by Callie Shelley
An adult īnanga, Galaxias maculatus, (photo: Shaun Lee).
During the late summer and early autumn months, a special congregation of tiny but mighty fish takes place in the Kohuroa awa (stream).
Īnanga (Galaxias maculatus) are a specialized freshwater fish that migrate between freshwater and marine habitats during different stages of their development. As baby fish, they spend their time in the ocean. As they grow into juvenile fish (commonly called whitebait), they slowly find their way to an estuary where freshwater and saltwater mix to continue growing into adults.
Adult īnanga are known to live in fully freshwater environments but once they are ready to reproduce, something fascinating happens. During February to May, īnanga return to the brackish (slightly salty) section of the estuary and make their way just above the water line to lay their eggs within the stream vegetation. Of the five whitebait species, īnanga is the only one with this unique ability.
“Inanga return to the brackish (slightly salty) section of the estuary… to lay their eggs within the stream vegetation.”
Potential spawning habitat within Kohuroa awa (photo:Benthics).
The Egg Hunt
Last year, an observation of adult īnanga was made in the Kohuroa awa at a community Spotlighting event. This raised the question as to whether the Kohuroa awa could provide essential habitat for the īnanga life cycle, and so further investigation of the stream banks was planned.
In May 2025, Hana Aickin and her colleague Sarah Dimitrijevic (Mountains to Sea Conservation Trust) set up a two part process to search for evidence of īnaga breeding around the time of the spring tides, when eggs are normally laid. The first step was to carry out a saline wedge survey to identify the upper limit of saltwater in the estuary and narrow down the search area. Once this was established, Hana and Sarah went about scouring the riverbank to look for signs of īnanga spawning and reproduction.
To their surprise, the survey was successful and an egg patch (1m x 0.65m) of approximately 8,500 eggs was found within the vegetation overhanging the awa (stream).
An īnanga, ‘egg patch’ found at Kohuroa awa (photo: Hana Aickin).
When asked if the Kohuroa awa (stream) had ever been checked for eggs before, Hana said, “The stream has never been on our radar, really. It was our first investigation. We knew there were adult īnanga in this space, just through fish trapping and finding gravid īnanga.”
The team was able to confirm that the eggs were alive by taking a closer look and identifying tiny eye spots. “Even the first time we went out,” Hana said, “we found the eggs, and they had eye spots. I was holding it on my finger, and the eye spots moved.”
“we found the eggs, and they had eye spots. I was holding it on my finger, and the eye spots moved.”
A single īnanga egg, positioned on Hana’s gloved fingertip (photo: Hana Aickin).
A significant discovery
The presence of viable eggs at Te Kohuroa is important because īnanga are known to return to the same place to lay eggs year after year, suggesting that Kohuroa awa (stream) is critical habitat for the species. This finding also emphasises the importance of continued monitoring for the stream habitat and raising awareness about vulnerable native species.
Currently, īnanga has a national threat status of “At Risk - Declining”, primarily due to the loss of spawning habitat through changes in land use and increased rural and urban development. Another risk to the survival of the eggs is nearby dog faeces, which can instantly kill the eggs.
Future action
Due to the valuable support of Mountain to Seas Conservation Trust and their Whitebait Connection program, Te Kohuroa Rewilding is now looking into strategies to protect local īnanga breeding sites including:
blocking off the area during spawning season (to prevent from dogs and humans)
increasing pest control measures
ongoing habitat maintenance and planting native vegetation along the awa (stream)
providing information and signage to educate locals and visitors about this unique species.
We will also continue to work with the Mountains to Sea Conservation Trust to bring community engagement events such as freshwater spotlighting to our community, and build our volunteer action groups for water quality and biodiversity monitoring to give our community a chance to get involved with īnanga conservation.
By protecting their spawning habitat, future generations can continue to appreciate this amazing fish at Te Kohuroa Matheson Bay.
Resources
Would you like to learn more about the lifecycles, habitats and breeding patterns of īnanga? Are you interested in surveying for this species within your local catchment? Then check out the amazing online resources from MTSCT
HERE.
About the Author
Callie Shelley is the Events and Engagement Coordinator for Te Kohuroa Rewilding and a passionate conservation advocate. She has worked within Aotearoa supporting community volunteer programs and holds a Masters in Marine Science. Callie has a special interest in fish species that reproduce above the high tide water line such as the [name of fish] which she studied.