Help Manage our Muskellunge

Cleithrum Project

How to Submit a Sample


Anyone can participate in the project by submitting the cleithrum bone either in a special envelope (provided by the Cleithrum Project) or in a ziploc bag with a copy of the envelope's form. If a fish is to be killed for eating, the angler can particpate directly; if it's to be mounted, then the angler can request the taxidermist to participate. If the taxidermist requires further information or envelopes, we can provide it. It is possible to make a quality mount from a fish with a cleithrum removed. Samples can be sent individually or in batches; please send in a rigid container to prevent breakage during shipping. The samples should be sent to the address on the form (the address is also available from the contacts section of this page).


If age and growth information of the fish is desired, please print or type a name and complete address on the envelope/form where indicated with "send age"; alternatively, we can send the information to an e-mail address (please still include a name).

Instructions for Removing Cleithral Bones

Text and photos from Casselman, 1979
Cleithra (singular - cleithrum) are paired, crescent shaped, flat bones that are the main supports of the shoulder girdle. They are just visible under the skin, on either side of the head immediately behind the gill covers. They are near the surface of the body and can be easily removed by hand. The step-by-step procedure for removing the cleithrum is detailed and illustrated below. The basic points for removing the left cleithrum by hand are as follows:


  • A. Hold the fish with the head facing left, and grasp the fish behind the pectoral fins with the right hand. Hold the fingers of the left hand over the top of the head.
  • B. Use the thumb of the left hand to lift the opercular flap (gill cover), exposing the cleithrum just posterior (behind) to the gills.
  • C. Push the thumb between the posterior edge of the cleithrum and the connective tissue and muscle.
    D-E. Move the thumb towards the top, and then towards the bottom, to separate most of the inner surface of the bone from the underlying soft tissue.
  • F. Push the thumb or index finger of the left hand through the soft connective tissue in the middle anterior of the cleithrum.
  • G. Hook the index finger from the outside through this hole and firmly pull the cleithrum away from its dorsal connection, exposing the dorsal spine
  • H-I. When the dorsal tip has been released (in very large fish some of the heavy connective tissue may have to be cut away to ease the separation) grasp it between thumb and index finger.
  • J-K. Pull the cleithrum out from the body and towards the anterior (front of the fish). This will expose the anterior tip. It is important during this process to pull the cleithrum strongly away from the body to avoid breaking or tearing the extreme anterior tip and growing edge.
  • L. Push the cleithrum over the thumb of the same hand or the index finger of the other hand to hold back the adhering soft tissue. This peels away the muscle and connective tissue from the outer surface of the cleithrum
  • M-N. A clean cleithrum showing annuli (curved lines) indicating age.



With this method of removal the cleithrum comes away virtually free of soft tissue. If age is to be determined immediately it is sometimes necessary to scrape away any remaining soft tissue with a knife. Otherwise the bone is kept damp until boiling water is available with which to thoroughly remove the soft tissue. Bones must be thoroughly cleaned of muscle and skin before being sent through the mail to prevent putrifcation in transit.


Instructions for Cleaning Cleithral Bones

After one or both of the cleithral bones are removed from the fish the bones should be kept damp until they can be cleaned. If this is to be more than a day, they should be kept frozen. Be sure that the appropriate information remains associated with each cleithrum during this intermediate step.


  • Pour boiling water into a pyrex or other heat-resistant container.
  • Holding the bone with a pair of tongs or forceps, dip the bone into the boiling or near boiling water, and hold it there for approximately 15 seconds. Remove the bone and dip in cool, clear water. Rub off the muscle and other soft tissues with a cloth, paper towel, or tooth brush. If some soft tissue still remains firmly attached, repeat this process until all the soft tissue is removed. Twice is usually adequate except for very large bones, or those on which a lot of connective tissue has been left attached.
  • Then rinse the bone with clean water and wipe dry with a cloth or paper towel.
  • These bones can then be placed directly in the envelopes or ziploc bags. For each fish complete the information on the envelope/form, include the bone and scales, seal, and return to the Royal Ontario Museum.


CAUTION: Do not leave the bones in boiling water for more than 5 minutes or the zones used to determine age will become completely obscured. If processing several fish at one time, be careful to make sure that the bones, scales, and information from one fish are not mixed with those of another fish. If there is any possibility a mix-up has occurred discard both samples. 


Instructions for Taking Scale Samples


  • If the fish is to be mounted remove scales from the side of the fish to be slit.
  • Approximately 10-12 scales from the scale sample area indicated in the figure above are needed.
    Remove scales by lifting the exposed edge and pulling firmly on each scale. Do not remove scales by scraping backwards as in scaling a fish. Scraping breaks the surface of the scales and makes determination of age very difficult.
  • If fewer than 8 scales are removed examine them by eye in front of a light to be sure that at least some of them have complete concentric rings to the very centre. Scales that have been replaced have no rings in the centre area and are useless for age determination
  • No cleaning is necessary. Place the scales directly into the envelope for that fish or wrap them in a small piece of paper and then place them into the ziploc bag for that fish.

Instructions for Completing the Information Part of the Envelope


    Muskellunge or Pike or Hybrid.
    This is a number which will be assigned at the ROM ... do not fill in.
    If you have assigned this fish a number in your records, provide this number.
    Use June 5 or 5 June, '97 or 1997. Do not use 5/6/97. That can be interpreted as 5 June or 6 May '97. Date of Capture helps us determine how much of the latest growing season had passed at the time the scales and cleithrum were taken and/or the fish killed.
    This is the location of capture of the fish. Be as precise as you can. Mention nearest town if the lake or river is small or unnamed. Indicate county or similar geographical subdivision or province or state, since there are hundreds of lakes with such common names as Sand, Deer, Loon, etc.
  • SEX
    If when the fish is eviscerated, enlarged grey-white testes, or obvious flesh coloured or yellowish egg-bearing ovaries are apparent, then record sex by circling the appropriate word. The testes are solid strips of material whereas the ovaries are sac-like, translucent material. If the ovaries are cut crosswise the sac is apparent. It has a central cavity which is either empty or contains eggs in various stages of development. Even when very small, these eggs may be visible on close examination. The testes are solid in cross-section and gelatinous. Do not record sex if you are in any doubt; on gross examination the ovaries of an immature female look quite like the tests of a non-ripe male. If in any doubt, circle the question mark. When sex is included on an envelope, tell us how sure you are, or the reasons why you were unable to be certain. Specimens which have been frozen and thawed present an even greater problem for sex determination.
    If possible, give total length (see the figure in the scale removal section) in inches to the nearest quarter inch or in centimetres.
    Give weight whenever possible in pounds and ounces (or kilograms), but indicate whether it was weighed at time of capture or at time of mounting.
    Statements concerning the general condition of the fish help to interpret the marks on the scales and bones. Was it heavy with fat when eviscerated? Was it short and deep-bodied? Was it long and snake-like, with an overly large head? If scales exist, either loose or on the food fish, remove a few and wrap them in a small piece of paper (3 x 4 inches) and put them in the envelope/ziploc bag. From these scales we can determine the species, age, and approximate size of the fish that have been eaten by the muskie or pike. The reverse side of the envelope/form can be used for any information you think will be useful.
    Somewhere you can write girth in inches if you took it and you wish to include it. It is not a particularily dependable measurement since it is easily affected by time since feeding, time after death, and the treatment the fish received after removal from the water.
    It would be helpful if you could include some information on what the fish has eaten. Record whether the stomach was empty or contained food (Note: If using the form rather than the envelope, please include this information under 'Remarks'). We are interested in the size of the food items muskellunge eat. The ultimate size that muskellunge reach may be related to the size of food available. Help us test this relationship. If identifiable fish-remains exist in the stomach try to describe the number and size that were eaten either in weight (pounds and ounces) or length (inches).
    Complete by printing or typing if the angler or taxidermist wishes to learn our "good as possible" age determination from scales and cleithra. There will be no reply if name or address are not perfectly legible. NOTE: E-mail addresses are acceptable as well.
    Provide a good photograph of the fish if available; it is for scientific purposes and will not be used otherwise unless written permission is obtained.