For a more detailed list of alternatives, see Dr. ![]() However, other approaches work better for some fish. This approach works well for most fish species. store dry in a paper envelope until you're ready to age them.clean off the otoliths with water or your fingers.they won't be attached to anything other than soft tissue.they may or may not be resting inside hollows in the base of the skull.the large pair of otoliths should be visible underneath the rear of the brain, still inside the skull.push the rear of the brain to one side, or cut it out all together.very often, this exposes the otoliths and allows them to be removed immediately.this should snap a portion of the skull, and push the brain and otoliths up.once the brain is visible, expose the brain even more by pressing the nose and body down and towards each other.note that the brain joins the much narrower (but still white) spinal cord at the rear.an ideal cut removes the top of the skull, revealing the full length of the soft white brain underneath.if you haven't, make another slightly deeper cut.check to see if you've cut the top off the skull.for flatfish and some other species, a vertical cut through the top of the skull directly over the preopercle (the curved line 3/4 of the way back on the gill flap) also works well.you should feel the knife cut through the top of the skull.slice back and down about 1 head length. ![]() slant the blade away from you, at about a 30 degree angle.put the knife blade on the top of the fish's head about 1 eye diameter behind the eyes.lay the body of the fish on a counter with the tail pointing away from you.grip the head of the fish by putting your thumb and forefinger in its eye sockets.you'll also need a pair of forceps or tweezers about 10 cm long.the blade should be as sharp as possible.use a knife with at least a 15 to 20 cm blade.Smaller fish, such as minnows, may require the use of a microscope. Marine fish such as cod and haddock have otoliths which are relatively large and therefore easy to find (about 1 cm long in a 30 cm long fish). With a little practice, the large pair of otoliths (the sagittae) can be removed in 15 seconds. Otoliths of adult fish can generally be removed with nothing more than a sharp fish knife and a pair of forceps or tweezers. Even the size of the otolith can be used to indicate the size of the fish that was eaten. ![]() The otolith shape is so distinctive that biologists can use otoliths recovered from seal and bird stomachs and droppings to determine the type of fish they ate. That is, different fish species have differently shaped otoliths. Otoliths have a very distinct shape, which is characteristic of the species of fish. This one-way growth process explains why otoliths can form and retain such delicate structures as daily rings, whereas bone cannot. New otolith material can be (and is) added to the outside surface through time, but existing material can't be removed. The growth of the otolith is a one-way process. This property makes them more durable than bone. However, despite their size, the smallest pair (the lapilli) is most often used for daily ring ageing. The smaller pairs are about the size of the tip of a pin. The largest pair is usually used for determining age. There are 3 pairs of otoliths in each fish, including 1 large pair (the sagittae) and 2 small pairs (the lapilli and the asteriscii). They aren't attached to the skull, but rather float beneath the brain inside the soft, transparent inner ear canals. These pearly white stones are about the size of a pea, and can be found in the fish's skull just below the rear of the brain. Otoliths (ear stones) are found in the head of all fish other than sharks, rays and lampreys. ![]() Otolith definition, how to remove otoliths and determine age.
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