Algonquin Adventures / Determining the age of Lake Trout

**Posted by Treater** 9/01/2015 12:14 pm

We caught a couple of beauties last weekend and my son asked how old these fish were. Dads are always supposed to have an answer. And telling him to google it didn't seem right sitting in the park at the time.
I know that there are some trout experts on here so..... How do you determine, or is there a way to determine the age of an AP lake trout? Is there a correlation between length and age, or weight and age. Or is it something else?

**Posted by RobW** 9/01/2015 12:47 pm

If you just want a ballpark, then a 1 - 1 1/2 lb trout is probably 2-3 years old. The growth rate slows down as the fish get older so the bigger the fish, the less meaningful a guess will be.

There may be an update to this, but way back when I was taking my Ichthyology (study of fish) course at university, the way to age trout was by counting the rings on the ototliths which are parts of the inner ear. They grow rings kind of like trees do.

For some other fish you can count lines on the scales, but I don't think that applied to trout.

**Posted by frozentripper** 9/02/2015 7:58 am

There is a table showing "average" length at age several pages down at this link... many of the LT caught in APP will be <10 years old, so could be a rough guide. Length at age will vary from lake to lake (eg. Louisa LT growing more slowly due to planktivorous diet), genetics and variation in individuals.

http://www.bucklake.ca/misc/FishBiology.pdf

The oldest LT I've seen was one from Temagami about 35 years old caught during the eighties sometime... I can't remember the length and weight but it was a large trophy-sized fish. Aged by means of the otolith method described by Rob which involves lab preparation and time.

A quicker way to get an idea of fish age is to examine the flat opercular bone (the gill cover - cleithrum). It may need to be cleaned in boiling water first. Holding it up to the light should show some of those growth rings (annuli) that indicate age. Below is a cleithrum from a four-year-old-plus yellow perch. LT annuli may be less distinct, still, worth a look if you've caught a large one and not releasing.

PS... scales will also show annuli but since they're small, may need a hand lens or microscope. LT scales are very small and difficult to age but the annuli are there esp in younger fish.

Last edited by frozentripper (9/02/2015 8:02 am)

**Posted by Treater** 9/02/2015 4:15 pm

The only measurements we got were length. Too bad I didn't know the gill cover thing.
Thanks for the info!