[Histonet] histology of larval fish olfactory apparatus

[Jonathan Shenker]

One of my graduate students is attempting to characterize the ontogeny of the olfactory apparatus of larval fishes, specifically the leptocephalus ("slender head") larvae of tarpon/bonefish/eels, and to develop a comparison with olfactory morphology in larvae of other fishes.

She's interested in using fluorescent staining with confocal microscopy of whole larvae and histological sectioning of the olfactory apparatus and nerve, as well as employing more traditional histological staining techniques to visualize the olfactory pits, sensors, and neurons that innervate the organ.  She'll also use SEM for high-resolution imagery of the physical structures on the surface of the heads of the larvae.

My lab is pretty good with fish biology and ecology, but we're novices when it comes to histological analysis of tissues.  As we got into the literature on fluorescent, visual, and histological stains of neurons in general, we quickly got overwhelmed with variety of stains and techniques that have been used, but the literature seems pretty sparse on olfactory apparatus of fish larvae.

If Histonet folks have any advice on stains and staining protocols that she can use to visualize the components of the olfactory and nervous system of these transparent larvae, we'd be very appreciative of the guidance.



A quick guide to Leptocephali:  these larvae are beautiful, transparent laterally-compressed ribbons, clear as glass, with tiny heads.  They typically hatch into 3-4 mm long larvae, and grow to different sizes (tarpon = about 25 mm; bonefish about 50 mm; an unknown eel species has a larva that reaches nearly a meter in length).



Why are we focusing on leptocephalus olfaction?  Lepto olfactory pits are about as big as their eyes; their early retinas are rod-based w/out cones, so they can't see plankton particles (most higher teleost larvae have densely-packed cones in their retinas that help them visualize planktonic prey, and they have small olfactory pits); leptos have long projecting teeth (fangs) that suggest they "carve" chunks out of mucous aggregates called "marine snow" and gelatinous plankton for food; and the stable isotope signature of their bodies closely mirrors that of marine snow.



How do they find their food?  We're betting on olfaction/chemosensory cues, but we'd like to confirm that hypothesis with morphological and histological characterization of their olfactory apparatus, and hopefully combine it with behavioral analysis of live larvae (if we can get them).  It'll make a very interesting study.

Any suggestions about how to visualize their olfactory apparatus will be greatly appreciated!



Jon



Jon Shenker, Ph.D.
Associate Professor of Marine Biology
Department of Biological Sciences
Florida Institute of Technology
150 West University Boulevard
Melbourne, FL 32904
321-674-8145
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"...a constant stream of eager young folk, men and women, come to me with the same query. 'My present
work is dull.  How do I become an ichthyologist?'"  J.L.B. Smith, 1956 "The Search Beneath The Sea."
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