Aging Fish: Scales and Otoliths

[BeeGuy]

Well,

I haven't done this in many years, but we caught a sizable RMWF the other day and I figured I'd try and age it based on the scale annuli.

Anyone ever do this?

I have a dissecting scope at home with max mag of only 24x, but we'll see how she goes. I'll try and post some pics if it works out.

Aging based on the otolith is beyond my kitchen table science bench, and my little lady's fish stink tolerance.

[The Fisherman Guy]

I have seen it done on salmon on the west coast. Split the head with a very sharp knife directly down the middle from the top, between the eyes. Using tweezers, pull out the Otoliths out with tweezers and examine the lines using a microscope or magnifying glass.

Like counting the rings on a tree, although I am not a biologist, and could very well be mistaken.

Keen to know how it turns out BG, if you can post pictures of the process, I am sure many people would be interested to see how it's done.

[WayneChristie]

Id be interested in seeing the process too. both of them!

[Guitarplayingfish]

I also read that it is counting the rings, similar to a tree but on the scales.. good luck!

[WayneChristie]

Originally Posted by BeeGuy

Well,



Aging based on the otolith is beyond my kitchen table science bench, and my little ladies fish stink tolerance.

little old ladies or just ladies in general?

[BeeGuy]

Looks like about 5.5yr old female to me. Now for the second one.

Otoliths are a mission for another (spring) day.

[BeeGuy]

Interestingly, the much smaller bodied male seems to be from the same age class.

Sorry no pic.

[BeeGuy]

Originally Posted by BeeGuy

Looks like about 5.5yr old female to me. Now for the second one.

Otoliths are a mission for another (spring) day.

On second thought, given that the fish spawn in the fall, this fish is likely right at year 6.

Kinda cool.

I wonder how old they get.

[BeeGuy]

Table 4. Mean length at age for selected BC populations of mountain whitefish.

..........Age..0..... 1..... 2....3... 4..... 5.... 6.... 7.... 8... 9... 10
River
Columbia.138 210 270 304 341 355 370 375 373 401 432
Nechako....91 175 232 250 281 300 319 336 349 360
McGregor..63 102 156 191 210 229 247 269 284 309 312
Peace........93 172 220 249 273 295 323 342 365 369
Liard..........52 110 168 227 278 314 336 354 394 421 426

Taken from:
The mountain whitefish (Prosopium williamsoni ): a potential
indicator species for the Fraser System.

J.D. McPhail and P.M. Troffe




Our population is closest to the Columbia.

[goldscud]

We used to get otoliths from the bottom side (above first couple of gill arches). Once removed, we "sanded" them on a wetstone to get a flat surface before counting the rings. Sure helps if they are not too cloudy

[TyreeUM]

awesome post! Thanks for putting this on the forum. Are you retired?

[The Fish King]

I have had to do a couple hundred otoliths in the last year as part of a research project. They were rainbow, cutties, and brookies but the method should be similar for any fish species.
WE used the break and burn method...basically once you remove the otolith, take a scalpel and slice the otolith in half width ways.

Take an oil lamp or something with a small flame and lightly pass the otolith through the flame until it turns a dark brown. Dont overdo it or the otolith basically becomes charcoal and you cant read a damn thing.

Next, place the otolith in some clay so it can stand up under the scope for you. Finally, put a small amount of glycerol on the otolith. This clears the otolith and makes it about a million times easier to read the annuli rings. Some people get away with just using water but I find that it is much easier to read with glycerol.

Cheers and happy counting!

Scales are a very poor choice for whitefish. Otoliths are the only way you'll get a good reading as scales are tough to read (though the rings may seem obvious). There's a great Alberta fish aging book available, check you're local library, I can't remember the authors.

[Gust]

Originally Posted by TyreeUM

awesome post! Thanks for putting this on the forum. Are you retired?

I think the two of you are twins seperated at birth. Seriuosly, you two bio-dudes have special horseshoes up your arsenal. By the way Beeguy fishes, I would say he is of the Freedom 30 club.

[BeeGuy]

Originally Posted by GustavMahler

I think the two of you are twins seperated at birth. Seriuosly, you two bio-dudes have special horseshoes up your arsenal. By the way Beeguy fishes, I would say he is of the Freedom 30 club.

I tried Freedom 25, but it didn't last long. When freedom comes easily, it is easily lost.

Pretty much lookin down the barrel now.

[Fishtech1986]

The Fish King I have had to do a couple hundred otoliths in the last year as part of a research project. They were rainbow, cutties, and brookies but the method should be similar for any fish species.
WE used the break and burn method...basically once you remove the otolith, take a scalpel and slice the otolith in half width ways.

Take an oil lamp or something with a small flame and lightly pass the otolith through the flame until it turns a dark brown. Dont overdo it or the otolith basically becomes charcoal and you cant read a damn thing.

Next, place the otolith in some clay so it can stand up under the scope for you. Finally, put a small amount of glycerol on the otolith. This clears the otolith and makes it about a million times easier to read the annuli rings. Some people get away with just using water but I find that it is much easier to read with glycerol.

Cheers and happy counting!

Great Post, exactly how its done. Here are some pictures of some cracked and roasted walleye otiliths, see if you can figure out the age...

[BeeGuy]

7 years

[Fish-killer]

I would say 7 as well.

[Fishtech1986]

they are 3 different fish with 3 different ages

[BeeGuy]

Originally Posted by fishtech1986

they are 3 different fish with 3 different ages

7, 6, 11

[hl649]

BeeGuy said:

Table 4. Mean length at age for selected BC populations of mountain whitefish.

..........Age..0..... 1..... 2....3... 4..... 5.... 6.... 7.... 8... 9... 10
River
Columbia.138 210 270 304 341 355 370 375 373 401 432
Nechako....91 175 232 250 281 300 319 336 349 360
McGregor..63 102 156 191 210 229 247 269 284 309 312
Peace........93 172 220 249 273 295 323 342 365 369
Liard..........52 110 168 227 278 314 336 354 394 421 426

Taken from:
The mountain whitefish (Prosopium williamsoni ): a potential
indicator species for the Fraser System.

J.D. McPhail and P.M. Troffe

Our population is closest to the Columbia.

I believe that a large number of the fish referred to in these studies were caught by myself. We used to work quite a bit with McPhail back in the old days. I spent the better part of 5 years on the Peace and Columbia rivers. I tagged over 200,000 fish in the Columbia River alone with 250 of them getting radio transmitters implanted.

Goldscud said:

We used to get otoliths from the bottom side (above first couple of gill arches).

When I started with DFO in Nanaimo I showed this to a few of the folks there and they were absolutely amazed how easy it was to get them out from the bottom. They had never seen this before.

Jrs said:

Scales are a very poor choice for whitefish. Otoliths are the only way you'll get a good reading as scales are tough to read (though the rings may seem obvious). There's a great Alberta fish aging book available, check you're local library, I can't remember the authors.]

The book you mention is titled "Fish Aging Manual of Alberta". It is authored by a large number of people. I had a reasonable contribution to the rewrite of the 2nd version and contributed quite a few pictures for the final print.

Fishtech1986 said:

Great Post, exactly how its done. Here are some pictures of some cracked and roasted walleye otiliths, see if you can figure out the age...

Try using fin rays for Walleye. They are easier to read than the otoliths.


Just my $0.02

[jstelfox]

Originally Posted by BeeGuy

I wonder how old they get.

If harvest rates are high, very few mountain whitefish survive more than 10 years. However, in Spray Lakes Reservoir, where exploitation rates for mountain whitefish are quite low, I found that about 25% of the mountain whitefish that we gill netted were older than 18 years (the previously recorded maximum age for this species), with the oldest being a remarkable 29 years old. If you were to have tried to age this fish with scales, you wouldn't have seen more than about 7 or 8 annuli, which is why otoliths are better for ageing than using scales.

[BeeGuy]

Originally Posted by jstelfox

If harvest rates are high, very few mountain whitefish survive more than 10 years. However, in Spray Lakes Reservoir, where exploitation rates for mountain whitefish are quite low, I found that about 25% of the mountain whitefish that we gill netted were older than 18 years (the previously recorded maximum age for this species), with the oldest being a remarkable 29 years old. If you were to have tried to age this fish with scales, you wouldn't have seen more than about 7 or 8 annuli, which is why otoliths are better for ageing than using scales.

Thanks for that. I'll pull some otoliths out of the larger individuals and compare the results to the scale annuli.

I suspect that the 1-5 yr age classes should be fairly easy to age based on the scales and length measurements.

[Speckle55]

I agree with John Stelfox on using otoliths.. both my World Record Pike(ice fishing) and Brook Trout(line class) were age by David Donald Canadain Fisheries using otoliths.. pike 25 years old 32# 5 oz .. Brook Trout 13 years old 12# 13 oz

[BeeGuy]

It is certainly the case, and clearly identified in the literature, that when aging old fish, scales are not appropriate.

[cube]

Originally Posted by jrs

Scales are a very poor choice for whitefish. Otoliths are the only way you'll get a good reading as scales are tough to read (though the rings may seem obvious). There's a great Alberta fish aging book available, check you're local library, I can't remember the authors.

For those that wanted to know the URL for “Fish Aging Methods for Alberta” is
http://www.google.ca/url?sa=t&rct=j&...57LTMQjEVYJyTA
Isn’t the internet great? You don’t have to drag your lazy duff off to some library that probably does not have what you’re looking for anyway.

Perfect. Yeah, its a good resource. I did lots of fish ageing a few years ago and have a hard copy here somewhere. I remember checking a bunch of pike (struggling) then seeing I should try cleithrum, worked like a charm. I definetly found otoliths could be tricky for trout, even when burnt sometimes. One stream in particular comes to mind, a very, very cold stream, where rings were not even visible on many otoliths. Length frequency gave us a good idea but it was amazing how hard aging became. We had a very very experienced biologist check them as well. Wasn't the first time he'd seen "opaque" otoliths so it happens. And bee guy, comparing is a good idea. We tried scales and otoliths from rainbows and found scales generally underaged any fish over 2 or 3. Was fun to play with.