Pond Boss Forums INTRO Questions & Observations Calling Dr. Willis

Dave,

Here's a northern pike vetebrae that when severed with a strong pair of scissors (when skinning one out for taxidermy purposes) shows distinctive rings. I've noticed this on all the musky and pike that I cut the vetebrae on. Think this could be indicative of annuli similar to otoliths? The vertebrae are almost impossible to cleanly severe, so one has to use a twisting motion to severe them, which results in this.

HI Cecil. I don't know the answer off the top of my head. Let me do some checking. Some of the marine fishes are indeed aged by cross-sections of vertebrae, as are some mammals. I just don't know if anyone has looked into their reliability for aging of pike and muskies.

OK, I did some searching around and could find no reports of vertebrae aging for musky or pike. That doesn't mean it hasn't been done, just that I couldn't find any reports on a quick search.

My search turned up pretty much what my feeble brain remembered. Lots of uses of vertebrae for marine fishes (sharks and tunas were especially common), but not much else.

I did send Cecil a paper that compared spines and vertebrae for aging channel catfish. I also sent him an overview paper that discusses the problems with accurate fish aging from all types of structures. If anyone else wants those, just let me know and I can email a copy.

My guess is that the rings probably do indicate age, Cecil. However, as you can see if the Campana overview paper that I sent, some validation would be necessary before we accepted those ages. It's still an art!!

Sounds like a good topic for a Masters Thesis or something!

Speaking of academia, I saw your quote in Outdoor Life Magazine. It is always fun to say "Hey, I know that guy!"

Dr. Willis,

Thanks for the information! One factor I could see on why there are no studies to validate vetebrae aging on pike and musky is it would require the killing of these highly prized game fish.

Thanks!

Svo - yes, it would make a great study topic. It would be a good training exercise for a young student, too. However, as Cecil noted, I suspect that Muskies Inc. might not want to pay for it given the lethal nature of the work.

I was a little nervous about the Outdoor Life article. We really don't need to recruit a bunch of people into the profession. We're like the marines: we need a few good men and women. However, I do know that they quoted me accurately. I use that same tired joke all the time, so there's no doubt that I said it.

P.S. Great picture, Cecil!!

Pardon my ignorance on the subject, but do pike and musky have otoliths that can be reliably aged? Perhaps a sufficient sample population could be obtained from taxidermists and anglers willing to donate carcasses? The student could then cross reference the vertebrae with the otoliths to attempt to find a correlation.

Just thinking out loud.

I would be glad to save vetebrae and corresponding fish board lengths and certified weights if anyone is intersted. And of course the otoliths for comparison. I get in about a dozen northern pike and musky per year. Mostly northerns as the musky purists usually release everything.

SVO -- do you want my job?? Man, what a thinker! Pike otoliths are small and crumbly, and we used to think they weren't good for aging because of that. One of my students recently imbedded them in clear plastic cement, and then sectioned them. It worked pretty darn well. Probably the most commonly used structure (a lethal one) is the cleithrum. That's the bone that supports the gill arch. We found them a little hard to age, and I've wondered about sectioning them for aging.

I've never worked with muskies, but I assume they would be similar to the pike.

Back in my days as a technician for the Department of Fisheries and Oceans, in the Canadian Arctic (89-92) I was ageing fish structures that had accumulated in their research facility of Yellowknife, NWT.

In cold climate (north of 60) where normal fish growth can slow to almost nothing, where fish can live for dozens of years, Cleithrum bones were proven ineffective to accurately age northern pikes.
I use to embed the otoliths in epoxy and slice them up with an Isomet Saw, mount the thin slices and read them with microscope. The comparison showed that cleithrums were under aged for that latitude. Pikes from Lake Winnipeg were, on the other hand correctly aged by the cleithrum as it read the same in the otoliths.

Lakers (lake trouts) from Great Bear Lake, NWT were aged often in the 50 to 95 years of age. (20lbs to 50lbs). And Lake Whitefish (Coregonus clupeaformis)from that lake were surprisingly under aged using scales as their otoliths shows ages almost double those read from scales. Oldest I read was 63 years old!

The back log was over 30,000 fish and by the time I left it was all aged, and DFO headquarters decided to not use scales anymore for whitefish and to double age pikes with cleithrums and otholiths just in case.

If your fish are in fairly warm water and life expectancy is no more than 15 years, I would trust the bone rings, as they are correlated to the overall growth. If you catch a huge, old, northern pike, then the bones might not be a good indicator.
And Dave, I did test with cleithrums in epoxy, sliced them and found them to be hard to read when they got too old. My understanding is that the otoliths' structure adds a layer of calcium each year, even if the fish is not technically growing physically anymore. Some kind of one way permeable membrane protects the otoliths from calcium depletion as very old fish have been known to regress in length and shrink somewhat (like we do…)

The very old trout we aged were always smaller than younger ones and had lost or not achieve the capacity for reproduction. In most cases fish die in those circumstances, but up there, they remained half frozen in time, becoming very old as no predators hunted them. Of course, these were not common.

For your information here is what a cleithrum looks like when you read the age:
http://www.suomenhaukiseura.com/kuvat/hauki/biologia/ika_cleithrum1.jpg

MP - thanks for posting! I guess that I'll give up my thought of sectioning the cleithra. We'll stick to the otoliths, as we are doing more and more of them all the time, and less of the other structures. We still use some scale analysis to get a general picture of growth over the first few years of life (3-4, perhaps). When we need to know age structure, we almost always have been using otoliths.

30K fish aged is one heck of a job! I suspect you've got more skill than nearly anyone else based on that background.

We too use that Isomet saw. Great tool.

Dave

I was digging in my old files of Yellowknife and found that picture showing me sampling northern Pikes. that was in September 91 and the ducks were in full migration at the same time... Ahh the good old days!

Mario -- great picture, both in the foreground and the scenery in the background. We don't see bedrock in most of the locations where I have worked in my career! Would I be right in guessing that some of your shift in location is a result of the shift of Canadian fisheries responsibilities from the government to some of the private consulting companies?

Dave, my time up north was over when my wife became pregnant and since her family was in Ontario and mine in Quebec, we decided that the northern adventures were over for us. We moved to Quebec and started into pond management instead and never looked back!

Indeed the private sector was taking more and more space into the government. In the end all my years upthere were term positions, contracts and sub-contracts and mostly fun and exciting!

Cecil, the really nice picture of the severed spine doesn’t look like bone to me, but I know less than nothing about what a section of a fish vertebral body would show. Not being one to let ignorance stand in my way, I will ask if, since you twisted the spinal column to get the separation to occur, could it have happened through an intervertebral disk? The center looks mushy. In a mammalian intervertebral disk, there is a central “nucleus pulposis” which looks and feels just as you would expect from that name. It is surrounded by dense fibrocartilage, the “annulus fibrosis,” which is not quite as well organized as the structure your section shows, but is oriented in the same way. (A “ruptured disk” in humans occurs when the soft center protrudes through a defect in the ring of fibrocartilage.) If this is a disk we are looking at, maybe the number of rings would not relate to age but to ?species or ?maybe they get more distinct with increasing size. Just a thought.
Lou

Sounds plausible heronblu considering I know almost nothing about the subject.

The number of rings does roughly correspond with what the potential age of a northern pike of that size taken in Canada would be though. But of course that could be coincidental. I think the only way to know would be to save otoliths and vertebrae of these fish and do a comparison. Perhaps do this on 50 or more fish?