catfish otolith preparation for age interpretation

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