Cleithrum Removal

What is a cleithrum? The cleithrum is a calcified bone structure located on either side of the opercula (pectoral girdle; see pictures). As fish grow, calcium deposits from each year of growth are laid down and begin forming distinct, viewable lines (growth annuli) similar to growth rings on tree trunks. While scales can also provide age data, they are much harder to accurately assess and become even harder with older fish.

Drs. John Casselman and Ed Crossman helped pioneer the use of muskellunge cleithrum bones to assess age and growth relationships across its distribution. This undertaking began in 1979 and is known to many as "The Cleithrum Project". Taxidermists probably contribute the largest number of cleithrum bones to the project, but anglers do as well after harvesting a fish or finding one dead. It is important information that can shed light on the potential maximum size or general growth rates a given body of water may have.

As part of the necropsy we performed last week, I was given a tutorial on cleithrum removal by (my partner in crime) Hedrik. He's well known within muskie circles, and perhaps to the chagrin of his partners (haha), for plunging his hands into a well decomposed, dry-heave-inducing dead muskie to remove its cleithrum bone for aging. I was excited to give it a shot!

Removing the bone is much easier than I expected, and becomes easier the longer the fish has been dead for. The procedure is simple: find the cleithrum bone at the edge of the gill opening, use your thumb to pry the bone loose from the connective tissue beginning from the bottom edge and moving towards the top, repeat until all connective tissue has been severed, pull the cleithrum down exposing the bottom/front tip, and continue pulling (if it does not come with relative ease some of the connective tissue may still be intact) until the bone lifts free from the flesh. Go slowly, if need be, to prevent breaking the bone.

For more pictures and more detailed step-by-step procedures visit: http://www.mnr.gov.on.ca/en/Business/LetsFish/2ColumnSubPage/STEL02_168800.html

Necropsy Notes: Injuries From Single-Hook

The last two posts and accompanying pictures were from a necropsy of muskie that succumbed to its injuries during our live-bait study. We used the necropsy to determine the extent of those injuries and where they occurred. The following are our findings.

It took just three minutes for this 38 inch muskie to swallow the sucker. Upon hookset, the 8/0 J-hook tore a roughly one inch hole in the esophagus. As the hook continued to move towards the mouth and through the esophagus it also nicked the liver which would have resulted in a fair amount of bleeding. The injuries did not stop there, however. The hook ruptured the coelom (membrane) and penetrated the pericardial cavity where the heart is located. The hepatic portal vein (delivers "dirty" blood to the liver where it is detoxified, and then to a set of capillaries that distributes it to the heart) was also nicked. The latter would have caused a great deal of bleeding, probably the bulk of bleeding we noticed. The hook finally settled just outside the esophagus

Nearly all major vital organs are located just below the esophagus. Had the hook turned the other way as it moved through the muskie's body it is possible the damage may not have been as severe. Nevertheless...

Picture 1: The scalpel is inside the pericardial cavity and is pointing to the tear in the coelom. Just left of the scalpel is the tip of the tong that was inserted down the muskie's esophagus to show the hole created by the hook.

Picture 2: Close up of picture 1.

Picture 3: The tweezers are inserted in the hepatic portal vein which was nicked by the hook. To the right is the tear in the coelom where the hook penetrated the pericardial cavity.

Picture 4: Pooled blood inside the pericardial cavity perhaps a result of nicking the hepatic portal vein or the atrium.

Necropsy Notes: General Anatomy

The heart, housed inside the pericardial cavity, is located between the pectoral fins and between each operculum (a.k.a. gill flaps). Fish hearts are two chambered compared to the four chambered hearts of humans.

Interestingly, powerful swimming fish (e.g., tunas, salmon, sharks, muskies) are not necessarily a result of their musculature make-up, but the amount of coronary circulation provided by small arteries that wrap the heart. However, not all fish have this type of circulation. Also, remember that arteries deliver oxygenated blood to the heart, whereas veins deliver DEoxygenated blood to the heart (where it can be reoxygenated). So, the coronary arteries that deliver oxygen to the heart muscle are IMPERATIVE to the performance and activity level of a fish. If these arteries become compromised (e.g., blocked) then cardiac arrest can insue. Hedrik pointed out that perhaps in warm water there is so little oxygen in the water and even less afforded to the fish during the angling event that mortalities at in warm water may be caused by heart attacks. This is purely conjecture, but is worth investigating next summer.

Fish livers are generally large (in sharks they may constitute over 1/3 of their total body weights), and the muskie's is no exception. A muskie's liver is located just below the esophagus and running along the stomach. [Far right, picture 1 and 2]. The dark colored object just left of the liver is the gall bladder.

Fish gonads are located along the top of the fish and below the backbone. In these pictures you can see this muskie is a female and full of eggs! [Update. Hedrik took a small portion of the ovaries and counted the number of eggs then extrapolated the total number of eggs using the length of the ovary. There were 606 eggs in a 29 mm/1.1 in segment of one of the ovaries. The total length of the removed ovary was 43.5 cm/17.1 in. I will forego reporting all the calculations, but there were an estimated 18,180 eggs (give or take) in this 38 in female. Scott and Crossman (1983) reported a range of 6,000 to 265,000 eggs in adult muskellunge. Hedrik's estimate falls well within the reported range!]

The creamy white tissue below the ovaries and lining either side of the pink tissue (intestine) are fat deposits.

When we caught the fish I noticed a bulge in its stomach, and during the necropsy had a chance to find out what was inside it! Perhaps not surprisingly, it was another white sucker of nearly identical size as the one we used to catch the muskie with. The sucker already in its stomach appeared to be extremely fresh, with hardly any signs of decomposition.

Necropsy Notes: Swim Bladder

This post is mostly for those from MuskieFIRST who read or participated in the "fizzing a musky" thread, but this is also meant as an educational tool for all muskie nuts.

Physoclistous: swim bladder has NO direct connection to the outside world.
Physostomous: swim bladder DOES have a direct connection to the outside world.

Muskies are physostomous (as Tfootstalker pointed out) and, as such, have an OPEN swim bladder system (as opposed to closed). In this type of system it is possible to obtain gases from above the surface, and may be one reason (in my opinion) why muskies porpoise.

So, where is the swim bladder in a muskie? It is located ABOVE most major organs (e.g., liver, stomach) and just below the kidneys and backbone. The swim bladder has a very thick membrane that was even difficult to cut with a scalpel.

Picture 1: The swim bladder is the white strip running horizontally and located just below my left thumb. You can see how high in the body it is located. Also, those are the ovaries I am holding back.

Picture 2: Close up of the swim bladder.

For those that thought they were expelling gases from the swim bladder by puncturing a small hole in the belly of the fish or near the pectoral fin, this is wrong. Perhaps there was some excess gas built up inside the intraperitoneal cavity and this method happened to work, but poking around AT ALL is a bad idea. Because these fish are physostomous, LIKE HUMANS, they can be burped. As Tfootstalker noted, gently rub their bellies from the rear (genital opening) toward their gills. This will cause any excess gas to be pushed through the pneumatic duct - which connects the swim bladder to the esophagus and is in turn connected to the outside world - and out the mouth.

Again though, please DO NOT attempt to fizz a muskie.

Electrofishing Muskies

The original project boat has since been converted into a smaller utility boat, but its main function now serves as an electrofishing boat (albeit on the small side). One of Dr. Cooke's other grad students, Chris Pullen, was able to fabricate a safety cage and all the associated rigging for the anodes. It came out looking very professionally done and I've been eager to get out and use it.

Today was my chance to see if we could electrofish a few muskies. There is a project being conducted by another member of Dr. Cooke's lab, Alison Colotelo, which involves heavy sampling across many different sites looking for four species of concern. Although most of the sampling has been completed, Alison agreed to help me try to shock a few muskies.

For those not familiar with electrofishing it involves sending rapid pulses of electricity into the water to temporarily stun fish. It is a very safe method of sampling when done properly, and is extremely efficient.

Why are we trying to electrofish muskies? We are interested in getting controls and "baseline" physiology from muskies NOT captured via hook-and-line. It is impossible to get true control fish as any method of capturing fish causes some deviation from homeostasis (normal resting physiology).

We decided to sample a smaller stretch of the Rideau River with a good population of muskies. Most of the morning was spent sifting through lots of different species - including walleye, bluegill, pumpkinseed, smallmouth bass, largemouth bass, yellow perch, rock bass, and smaller minnow species. However, the muskies evaded us... for a bit. Finally, after switching to our third location, a nice 34 inch male was shocked and quickly brought aboard. Within 15 more minutes we had another smaller muskie at 30 inches. These were the only two we took blood from, but we did manage to shock a small YOY (young-of-the-year) and another about 20 inches in length.

So how did these control fish compare to those C&Red? Their glucose and lactate levels were much lower than those that were angled. This shows that the angling event does impose some degree of stress on the fish, but the magnitude is still unclear and will require more controls to compare.

Bittersweet Day...

The sweet: We finally boated a fish in the live-bait study.

The bitter: It died.
Using a J-hooked sucker with a 3-minute time-to-hookset, the fish we caught today succumbed to its injuries. It was hooked just outside the esophagus, but I suspect the hook tore through tissue deeper within the fish.

No doubt some of you are reading this and screaming, "WHY ON EARTH ARE YOU USING J-HOOKS? THEY HAVE BEEN PROVEN TO KILL MUSKIES!" This is true (see Terry Margenau's "Effects of angling with a single-hook and live bait on muskellunge survival" published in 2007. There was also an article on the study in the August/September 2002 issue of Musky Hunter). However, muskies in that study were allowed to swallow suckers for an average time of 17 minutes and a range of 4-37.

In this study we are attempting to find a) alternatives to using J-hooks and b) ways to use J-hooks that still hook muskies but without them swallowing the bait. Therefore, we are testing using quick-strike rigs, circle hooks, and J-hooks with 1-minute and 3-minute times-to-hookset (times less than those used in Margenau's study).

Let me return to why we are using J-hooks at all. GENERALIST anglers (and perhaps some specialized) still use J-hooks. They are so pervasive that regulations banning their use are unlikely and would likely be nearly impossible to enforce. Therefore, changing angler behavior (through showing anglers there are better, safer ways to use live-bait that minimize injury and mortality) may be a better alternative to outright banning J-hooks.

So far we have hooked three muskies using quick-strike rigs. We could not boat all three, but did note that they were all hooked in the corner of the mouth.

The passing of this fish may provide additional evidence that using live-bait should be done actively (i.e., setting the hook immediately) to avoid deep-hooking and subsequent mortality. We have had other muskies pick-up suckers on J-hooks and have given them one or three minutes before setting the hook, but in all instances we could not hook any. This might suggest that the only effective way of using J-hooks is to let the muskies swallow the bait, something that Margenau showed causes significant mortality (83% over a one-year period), and something that he considers (as do I) "unacceptable for trophy muskellunge management".

Wanted!

The following is directed to the angler(s) that removed the transmitter from one of this study's fish:

If you removed the transmitter from the fish but released it, please contact me via email. By removing the transmitter you saved us $200 since it can be reused again. We got enough data from the fish before the transmitter was removed, but it would be helpful to know WHY the transmitter was removed.

PLEASE contact me if you have any information. If you'd rather speak by phone my cell is 1-217-649-4449.

Thank you,

Sean Landsman

Size May Not Matter?

I still have not run any statistical analyses on the data we've collected thus far, but today we added another muskie - 31 inch - to the sample which gave us some interesting results. After battling the muskie for four minutes, the blood glucose and lactate levels were almost exactly the same as the 43.5" caught the other day in 11.5C (~52F) water. The fish today was captured from 9C (48F) water and its glucose and lactate values were 3.2 and 7.3 mmol/l as compared to 3.0 and 7.2 mmol/l for the 43.5 incher. The lack of variation could potentially be explained in the water temp decrease, but is interesting to note that there was very little variation in blood glucose and lactate levels despite a size differential of over 12 inches.

"The eternal mystery of the world is its comprehensibility."

The study's largest muskie - a beautiful 52 inch specimen - has vanished.

Fish #1247's transmitter was found on shore. Before we jump to conclusions, let us explore several options that could have transpired...

Perhaps the muskie befriended Rocky the Raccoon and implored him to remove that annoying little transmitter. Is this likely? No.

Or maybe someone caught the muskie, filleted it on shore, and dumped the transmitter. Though the transmitters are light, they do sink when placed in water and thus could not have floated ashore. Furthermore, the backing was still attached - nay, seemingly hung - precariously from one of the two wires protruding from the transmitter. If the transmitter had fallen off the fish, the backing would be missing. Additional evidence pointing toward harvest includes cut marks in the wire and only one wire twist where there were originally five wire wraps used to tighten the transmitter on the fish.

Ah yes, but the plot thickens. This muskie was caught from the Ottawa River - an Ontario water body with a 54 inch minimum size limit. Therefore, at 52 inches this muskie could not have been legally harvested.

Why someone did not dump the transmitter into deep water, or throw it away somewhere far on shore is a mystery. It's as if the person wanted us to find the transmitter, but did not want to reveal themselves for fear of being fined.

One more potential scenario could have been carried out: the fish was caught by an angler(s) who removed the transmitter, released the fish, and put the transmitter on shore. Perhaps this angler(s) did not like someone messing with "their" fish. Perhaps they did not know this study existed? Maybe they did and had qualms with it? Maybe, maybe.

This will remain a mystery. Fish #1247 was tracked to this location a little over two weeks ago and tracked once more yesterday to the same location. When it was first tracked to this site I did not notice a rotting flesh smell or notice remains on shore (wasn't looking). However, had the fish been filleted on shore it is likely raccoons or other creatures would have made quick work of the remains. However, I don't think raccoons could or would have carried off the bones. So why no bones? Did someone remove the bones AND skin? Or did the above more optimistic scenario transpire.

We may never know...

Water Temps, Angling Times, and Stress Levels

I compared the data from yesterday's 43.25 inch muskie to other muskies of similar size (43-45 inches). Just to compare...

Yesterday's muskie caught in 11.5C (52.7F): angling time = 3:40, glucose = 3.0 mmol/l, lactate = 7.2 mmol/l
43 inch muskie caught in 22.5C (72.5F): angling time = 0:55, glucose = 3.7 mmol/l, lactate = 11.1 mmol/l
45 inch muskie caught 18.5C (65.3F): angling time = 0:35, glucose = 2.6 mmol/l, lactate = 6.9 mmol/l

Let's compare one more fish that was given the gentle treatment...

44 inch muskie caught in 20.5C (68.9F): angling time = 0:54, glucose = 3.1 mmol/l, lactate = 7.1 mmol/l

It would appear that cooler water temperatures serve to suppress the stress response (despite long angling durations) given that fish angled in 1/3 or less the time show similar or even heightened levels. This may also be a finding that is independent of air exposure as evidenced by comparing yesterday's fish given air exposure and the above fish without air exposure).

Pretty interesting and some insight into how water temperature may influence your catch's chances at surviving an angling event. Hopefully next summer we will be able to compare stress levels in fish caught from 80+F water. However, my hypothesis would be that we would observe the opposite trend with fish caught from hot water: stress levels would be EXTREMELY elevated when fish are subject to long angling durations rather than seemingly suppressed as shown above.

Word To The Wise...

Check your line for frays. :(

Cold Streak Finally Warms

Last week I was finally able to track down suitable sized suckers for our live-bait study. I traveled 1.5 hours both ways to pick 12 suckers up. When I returned home I dropped them into a large container with water from the baitshop and an air stone pumping oxygen. Got up the next morning and drove to check on them... Half were dead! We fished with six live suckers and six dead ones. The dead ones we rigged on quick-strike rigs and cast, the live ones were put onto a mixture of circle hooks, quick-strike, and J-hook rigs. All our action came on the casted dead suckers now dubbed "Zombies". We had several hits that first day, but nothing could stay connected.

The above scenario has replayed itself several times now. The fish just don't seem to want the live stuff!

Today was a bit different, however. We had four pick-ups, but either the fish dropped the sucker after a short run or we whiffed on the hookset. Two were likely pike picking up the suckers judging by the unknown fish's inability to pull the float beneath the surface. The other two hits had more UMFFF behind them: one hit caused the float to rocket below the water and hang suspended about 2-3 feet down and the other hit sent line peeling from my reel like Jaws plucking a bluegill from beneath a bobber (before deciding the snack wasn't worth the effort).

Despite our failures to connect with any fish using live-bait, we had a bit more luck using artificials. At one point during the afternoon as we drifted a lush weed flat, the Bulldawg Hedrik so kindly lent me was smashed just as it was parting the water. The fish was small (under 30") and promptly got off. We took this as a good sign that the muskies might be starting to turn on. Towards the end of the flat, as I methodically worked Frankenstein (Hedrik inserted two screws into the Bulldawg's head to keep its nose down and prevent it from popping out of the water), I watched as a muskie slowly rose behind the bait, open its mouth, and quickly snapped it shut on Frankenstein. I hammered the hooks home and the fight was on! It was immediately apparent that the fish was hooked well, so I drew the fight out to test the fish's ability to cope with long fight times in cool water (just above 50F). The fight lasted almost four minutes.

What I caught was one of the (no offense to the muskie) gnarliest looking muskies I've ever caught. Skinny, splotched with scars, and weird "cracking" of its slime coat along its body made this one of the strangest fish I've ever encountered. In fact, it was so skinny that it looked much smaller in the water than it actually was. I was guestimating 38-40 inches as I was fighting it, but it taped out at 43 inches. The fish also appeared to be a male. If it's a male then in all likelihood this is an older fish which could explain why it looked so peculiar.

Regardless, it was another fish for the project! For those curious, the fish's glucose values were low and its lactate (7.8 mmol/l) was perhaps slightly above average, but well below the maximum we've seen (10-11 mmol/l) despite an almost four minute battle.

Back at it again tomorrow!

Skyscraper 'Skies... With A Twist!

After making a failed run to find suckers this morning (didn't stop to check store hours... apparently the place is closed on Mondays!), Hedrik and I decided a little fishing somewhere was just what the doctor ordered. The question was, where? We could not find a trolling motor to drift a section of river near downtown Ottawa, so we hooked up the boat and trailered it a block away from Little Italy!

Though the pasta with bolognese and vintage pinot grigio tempted us, the thought of seeing a hungry muskie chase down a lure was even more appetizing! We launched at Dow's Lake which is a 10 minute walk from Carleton University, and the site of many classes that Dr. Cooke teaches.

I started off the outing with a follow from a fish of unknown size on a bucktail. A little while later, Hedrik had another follow on a Bulldawg from a low-30s fish. We proceeded to fish the base of a restaurant where I got a follow from a knee-knocker of a fish (upper 40 inches, pushing 50). After that follow, things slowed for us. So, we returned to the location we began our day at.

I clipped on the same lure that got our first follow and cast it in nearly the same location as said follow, and WHAMMY (that's for all you "Anchorman" fans out there...)! Fish on! As the muskie came in towards the boat, I thought I caught a glimpse of a Floy tag. I didn't say anything because I didn't really believe my eyes, but once the fish was in the net I confirmed my first glimpse. There before us sat a previously tagged muskie! This was a fish from a study by Dr. Cooke and his students on the movements of muskellunge in Dow's Lake. The fish in the study were implanted with internal radio transmitters (as opposed to the external radio transmitters we are using), and hanging from the belly of this fish was a wire antenna protruding from a small incision! DE-CENT (for all you "Trailer Park Boys"/Bubbles fans...)! The fish taped out at 40 inches, and I am in the process of trying to get data on when it was first captured.

Unfortunately, the ramp at Dow's Lake closes at 5PM so Hedrik and I had to leave despite getting two more HOT follows from 42-43 inch fish. I was having an internal battle with myself about whether to go home and walk to Dow's, when Hedrik suggested we move to another stretch of river downstream from Dow's Lake. Obviously, this was a good idea so we trailered the boat again and moved down to Mooney's Bay on the other side of Carleton's campus.

We didn't have much time to fish, so Hedrik took me to one of his best producing spots. I clipped on a Tuff Shad (crankbait) and hoped it would finally catch me a fish (never has). I wasn't let down as at the deepest portion of the bait's dive curve it came to a complete stop! I hammered the hooks home and could feel hard, gut wrenching headshakes. The fish then proceeded to zip around the boat like a torpedo from the USS Viriginia, roll, zip around some more, roll, take another drag peeling run, dive beneath the boat, and roll some more. After all these wild antics, the fish finally rolled so much in the line that it basically entangled itself and I was easily able to guide it into the net. I can honestly say this was the friskiest fish I've ever caught! It wouldn't even hold still in the trough (a rarity)! This fish taped out at just over 40 inches.

All in all, it was a good day! Now if we can figure out where to get those darn suckers... :)

[That's the Dunton Tower (houses a variety of different institutes, schools, and departments) at Carleton in the background of the first picture, and what look to be office buildings in downtown Ottawa in the third picture.]

Tracking Confirmations

There is a fish that has been hanging out next to the ramp on the Long reach of the Rideau River the last several times I've gone to track it. I was getting worried because it seemed to be in the same location, or nearly the same location, each time I'd go to track it. When we stopped at the ramp I turned the receiver on and pointed the antenna in the direction I'd been hearing it. Sure enough, it was still there. We launched the boat and zeroed in on the signal. The water was extremely clear and I could see down to the bottom in 3-4 feet of water. Finally, I got the signal down to its lowest setting and let us drift along slowly. As I scanned the water I noticed movement to my right where the signal was coming from. A puff of silt clouded the water and as I pointed the antenna at the point of disturbance, the signal gradually got quieter and quieter. That was good evidence that our fish was there and, most importantly, alive.

After completing the rest of our tracking on the Long reach we moved to the Eccolands stretch closer to downtown. I picked up the frequency of our first fish from this stretch of river (caught speed trolling a spinnerbait) and tracked it down. When I had the signal at its lowest strength I began scanning the water. It was deeper here so I did not expect to see anything. Just as I was about to turn around and grab the GPS to mark the location, the fish I'd been searching for came cruising RIGHT IN FRONT OF THE BOAT at the surface! I could see the transmitter, backing, and Floy tag clear as day! The fish stayed on the surface for less than five seconds before sounding into the weeds.

I am very pleased as this helps confirm that my tracking accuracy is very good!

The live-bait study will, hopefully, begin sometime this week. We are having troubles getting acceptable sized suckers, but things are progressing nonetheless. Stay tuned...