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Published byElla Aubrey Ramsey Modified over 9 years ago
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Catfish otolith preparation for age interpretation One method suited to working with the morphology of the lapillar otolith
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Three paired otolith organs : saccule, lagena, and utricle Usually the largest otolith is from the saccule – the sagitta and is the one preferred for age interpretation In catfish the utricular otolith – the lapillus is the largest of the three and is the one generally used for interpretation 2
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Whole lapillus from a Blue Catfish (BCF) -annuli not discernible - (ventral surface –note opaque macular hump in the center)
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BCF utricular and lagenar otolith - the lapillus and the asteriscus – (shown in “as extracted” condition ) 4
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Flathead Catfish (FCF) lapilli (utricular otoliths) 5
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BCF otolith – ventral/macular surface – cannot see much below the surface 6
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Dorsal surface – some annuli may be visible enough to provide orientation for mounting on glass slide 7
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FCF ventral/macular surface 8
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FCF lapillus - dorsal surface 9
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Options “clearing” -immersion in a medium that reduces opacity can sometimes reveal internal structural patterns (often used for sagittal otoliths that can be read (interpreted) whole “break and polish” – viewing in the transverse plane is often the preferred method for older (and thicker) otoliths thin section - usually with a wafering blade on a low speed isomet saw 10
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Or - find the transverse view (analogous to what is achieved with break and polish method) by grinding away part of the otolith to find--- 11
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Not all otoliths are that “cooperative” with strong, clear annuli The main objective is to determine the best transverse plane which captures a readable transect completely from the core to the outer edge 12
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Next – find a reliable way to get there: Thin sectioning works -but there are other ways that may be useful The lapillus is too “chunky “ to break and too small to hold onto by hand for grinding, so…… adhere the otolith to a glass slide to facilitate holding it reliably for grinding 13
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Mounted on slide 14
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“underside” 15
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BCF lapillus mounted “sideways” on a slide with the rounded (anterior) end hanging over 16
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Mount lapillus “perpendicular” to edge 17
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keep the grinding plane parallel to the edge of the slide 19
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Equipment and Supplies Glass slides – we use Fisher Finest Superfrost with clipped corners Waterproof sandpaper – usually 600 -1200 grit depending on size range of otoliths. Crystal Bond 509 “sculpey” type modeling clay – to hold mounted otolith slide in position for reading with stereoscope hot plate - Stereo microscope - with camera Fiber optic illuminator - and a piece of single strand cable (1.5mm?)we have a new LED one that seems good and was very inexpensive. (*We could still improve on the “adapter” for the piece of fiber optic strand ) Buehler grinder – Metaserv 2000 20
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The grinder 21
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Results vary – sometimes it’s the otolith, sometimes ----? 22 One benefit of the “grinding” method is the ease of monitoring the process and progress as you get close to the core; to be safe, it can be helpful to snap a few photos as you grind away just in case “a little more” grinding turns out to have been a bad idea.
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Transverse view of BCF otolith - 2 year old –note relative size compare to the edge of a glass slide
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3 yr old BCF 24
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1 yr old BCF 25
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4 yr old BCF 26
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4 yr old BCF 27
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7 yr old BCF 28
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9 yr old BCF 29
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4 yr old FCF 30
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11 yr old FCF 31
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11 yr old FCF 32
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17 yr old BCF 33
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Exciting day in the Age and Growth lab
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