Catfish otolith preparation for age interpretation
One method suited to working with the morphology of the lapillar
otolith
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
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Whole lapillus from a Blue Catfish (BCF) -annuli not discernible - (ventral surface –note opaque macular hump in the center)
BCF utricular and lagenar otolith - the lapillus and the asteriscus – (shown in “as extracted” condition )
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Flathead Catfish (FCF) lapilli (utricular otoliths)
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BCF otolith – ventral/macular surface – cannot see much below the surface
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Dorsal surface – some annuli may be visible enough to provide orientation for mounting on glass slide
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FCF ventral/macular surface
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FCF lapillus - dorsal surface
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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
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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---
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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
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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
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Mounted on slide
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“underside”
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BCF lapillus mounted “sideways” on a slide with the rounded (anterior) end hanging over
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Mount lapillus “perpendicular” to edge
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keep the grinding plane parallel to the edge of the slide
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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
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The grinder
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Results vary – sometimes it’s the otolith, sometimes ----?
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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.
Transverse view of BCF otolith - 2 year old –note relative size compare to the edge of a glass slide
3 yr old BCF
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1 yr old BCF
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4 yr old BCF
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4 yr old BCF
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7 yr old BCF
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9 yr old BCF
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4 yr old FCF
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11 yr old FCF
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11 yr old FCF
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17 yr old BCF
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Exciting day in the Age and Growth lab