Determining Age Of Fish??

[ladystrange]

this is a question posed to the Gurus of our sport, fish biologists and those with photographic memories who have read it in an article god only knows how long ago.

 

 

a friend asked me last week, how do you determine the correct and exact age of a fish and does it differ between species? is there a scientific way to tell how old a fish is?

 

i thought it over, rummaged through my copious books and the only thing i could come up with was the approximate average of 2 inches per year. and specifically that referred to the trout and char in Alberta.

 

he was more asking about Pike and walleye. he's a taxidermist and generally gets the big fish but all he does is form them and paint.

[Flytyer]

If memory serves me right most can be aged by examining the scales in some way.....can't be positive on this but think it has to do with rings in the scales?

[Guest tallieho]

I'd heard that they estimate there age by measuring the rings in there otelith [inner ear].It's a shame they have to kill them to do it thou.

[monger]

There is a few ways to age fish. Growth rings occur on otiliths (inner ear bone), scales and opercular bones. Different methods are used depending on the species of fish.

Growth rates are determined by food availablilty, water temperature and quality and other factors. Cold water really slows down the biochemistry in the body so fish in the far north tend to grow at a much slower pace than fish in more temperate water.

[sirocco]

Barry Mitchell's Trout Highway has a section on fish growth. I can't remember any details though.

[Taco]

general rule of thumb for troot in Ab- 2"/yr and 50% natural mortality

[ladystrange]

i was actually looking for the specific method

 

like counting rings of a tree. of course depending on the weather each season will depend on how big the rings are, but each ring represents a year.

 

since he is a taxidermist, the fish come to him dead anyway and he has to skin them so accessing the inner ear is possible for him. just wondering how to go about actually doing this.

 

monger, what method would you use for say Pike and true trout vs. char

[monger]

Miss strange, here are some useful links

 

http://www.fishsa.com/Age-Of-Fish.php

 

http://www.floridamarine.org/features/view...le.asp?id=21978

 

Aging Pike

 

http://www.for.gov.bc.ca/hfd/library/documents/bib103875.pdf

[rhuseby]

The method used by fisheries biologists for accurate determination is otolith sectioning. The otoliths are essentially small spherical bones in the fish's ear. They are removed , slices, stained and the rings counted. The method becomes less accurate on extremely long-lived fish. Fish ages vary widely from species to species, as do growth rates. For example browns and rainbows in the lower Bow will grow much more rapidly than fish in the upper Bow, due to access to more optimal water temps and much larger food supply. Because of where they evolved, these two species prefer warmer water, and can tolerate greater levels of pollution, than the native cutts and bulls, which need very cool and pure water. A highly interesting topic to discuss with a biologist.

[Harps]

There are varing method, how well each works is dependant on the type of fish.

 

Scales are excellent for aging trout (even long lived Ferox trout of Scotland can be aged with scales).

Easy to collect!! You have to be familiar with fish in an area to be good at aging scales...

 

Fin rays (cut like trees and viewed like rings) are non leathal for spiny rayed fish like walleye and perch.

 

Odoliths are very great and lethal... very common aging technique.

They have to be dried properly and then split... can be frustrating to get them perfect.

 

Vertabrae collections are also lethal to fish.

 

Cleithrum are used for pike and Opercular bones are good for pike.

 

The trouble is sorting out the real annuli from the false annuli (bad summers of no growth, etc).

Scales and operclum both have flase annuli that cn be confusing, even to experienced viewers.

 

Ladystrange,

If you have a scale sample, try scanning it and blowing it up (or take a picture through a dissecting scope) and posting a picture online. You could also take the scale to a F&W office to look through their dissecting scope (if you ask nice).

 

 

[SilverDoctor]

You could also apply these scientific rules.

 

Didn't feel it on my line - fingerling

Cool little fight and tremors - juvenile.

Good fight with a bit of line taken - nice trout.

Took me out to a bit of my my backing - wily big old trout.

Almost to the end of my backing - Ole mossback.

Snapped the leader - dam crafty trout (making long, motion with hands).

Wrapped around a rock - smart old Trout"

Snapped fly line - walk trembling away from river saying "Wholly *% bloody #@*& Trout" with glazed eyes

 

I believe these rules will quickly verify the age of any trout.

[ladystrange]

nice doc. that was funny.

 

thanks for all the help. i will pass on the information. since the fish end up with my taxidermist - already dead, i'm not too concerned about how lethal it is to the fish. but the scale idea might be more helpful to him.

 

i will take a look at those links too.

 

as always - the information and help is very appreciated

[rusty]

Harps,

 

A buddy and I have taken a bit of interest in the age of pike with all of the rhetoric floating around about killing large females. We fish Badger and Newell and Keho quite a bit and have kept and dried a few cleithrums (I'm assuming that's the bone directly in front of the pectoral fin, shaped like an L).

 

Most of the bones have a wide variety of bands with a few very dense markings. Do you just count these dense bands, or are you counting every single mark?

 

We have a cleithrum from a 43" pike that looks to be between 8 and 10 years old. That's quite a bit less than most info I found on the internet - is it realistic? The cleithrum from a 37" fish counted 7 as far as I could tell.

 

How old do you figure your standard mid February southern Alberta 20 pound gator would be?

 

If I had that 60mm f2.8 Nikon Macro I wanted I'd post some pics.

 

And, before anyone gets excited about smacking the occasional big pike on the head, please direct your passion and enthusiasm to the folks who make the regulations.

[dryfly]

If we are talking pike. The smaller (of the big ones) are males and no one cares how old males are.

 

The really big ones are females and I sure as hell will not get into a discussion about the age of females and the fact that they may be 'heavy" .. talked about double-edged sword. That's a lose-lose situation for a guy. :P

[dryfly]

Seriously..

 

rusty..just saw your question, "How old do you figure your standard mid February southern Alberta 20 pound gator would be?"

 

From ACA study in 1999. For Badger Lake....the 9 and 10-kg pike netted were 10 and 11 years old.

 

For Keho the 6 to 8 kg pike were 8 and 9 years.

 

A mid February female would likely be heavier than summer (netted) pike since it would be laden with roe.

 

Clive