Catfish otolith preparation for age interpretation

1. Catfish otolith preparation for age interpretation One method suited to working with the morphology of the lapillar otolith

2. 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

3. Whole lapillus from a Blue Catfish (BCF) -annuli not discernible - (ventral surface –note opaque macular hump in the center)

4. BCF utricular and lagenar otolith - the lapillus and the asteriscus – (shown in “as extracted” condition ) 4

5. Flathead Catfish (FCF) lapilli (utricular otoliths) 5

6. BCF otolith – ventral/macular surface – cannot see much below the surface 6

7. Dorsal surface – some annuli may be visible enough to provide orientation for mounting on glass slide 7

8. FCF ventral/macular surface 8

9. FCF lapillus - dorsal surface 9

10. 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

11. 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

12. 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

13. 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

14. Mounted on slide 14

15. “underside” 15

16. BCF lapillus mounted “sideways” on a slide with the rounded (anterior) end hanging over 16

17. Mount lapillus “perpendicular” to edge 17

18. 18

19. keep the grinding plane parallel to the edge of the slide 19

20. 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

21. The grinder 21

22. Results vary – sometimes it’s the otolith, sometimes ----? • 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. 22

23. Transverse view of BCF otolith - 2 year old –note relative size compare to the edge of a glass slide

24. 3 yr old BCF 24

25. 1 yr old BCF 25

26. 4 yr old BCF 26

27. 4 yr old BCF 27

28. 7 yr old BCF 28

29. 9 yr old BCF 29

30. 4 yr old FCF 30

31. 11 yr old FCF 31

32. 11 yr old FCF 32

33. 17 yr old BCF 33

34. Exciting day in the Age and Growth lab