Tagging of Hatchery Fish

November 30, 2023

Question: What’s the purpose of putting tags in salmon that are released from hatcheries?

Answer: CDFW implants millions of fish each year with tiny metal tags engraved with codes indicating when and from which hatchery a fish was released into the wild. When the salmon return to their release location a few years later, CDFW scientists collect that important information.

The fish are about five months old, living and growing in a hatchery raceway, when they’re brought in for tagging. The adipose fin on the fish (between the dorsal fin and tail fin) is also clipped, which is a visual indicator of which fish have the metal tags, and which ones do not.
The tagging happens at several CDFW hatcheries each year. At the Nimbus Fish Hatchery, east of Sacramento, about a million fish are tagged annually. The fish are about three inches in length when tagged. At roughly the six-month mark, the fish are released.

CDFW Interpretive Services Supervisor Laura Drath explained the importance of tagging salmon.
“The information on the Coded Wire Tag allows us to assess the success of our practices,” said Drath. “We're seeing not only how many hatchery-bred fish are returning, but also which of our release sites are most successful.”

The information retrieved from the tags helps CDFW monitor and adjust management techniques if needed. If a release site is not yielding a good return that site may not be used in the future. CDFW’s goal is to keep the fish population sustainable by using these tools and strategies.