Re: NANFA-L-- mudminnow fry

dlmcneely-in-lunet.edu
Fri, 13 May 2005 17:29:07 -0500

First, I have never looked-in-a larval, or even adult, mudminnow caudal
fin closely, so this will be somewhat speculative.

In all bony fishes, the terminal vertebra has an extension called the
urostyle. In most fishes, this urostyle continues the vertebral column
along the dorsal edge of the caudal fin, though it is not prominant
(and indeed is substantially shorter than the lobe itself) in those
with a homocercal (equal lobed) tail. In gars, and most others with a
heterocercal tail, this urostyle is quite long as it extends to near
the end of the dorsal lobe of the caudal fin. The caudal fin membrane
is supported by rays that are in turn supported by bones called
hypurals (fused in many into a nearly solid "hypural plate"). These
are the elongated and flattened haemal (ventral) spines of the last
vertebra. There are also epurals, dorsal to the position of the
urostyle, and formed from the neural (dorsal) spines of the last
vertebra. This anatomy may be seen on page 30 of my 1st edition of
Helfman, Collette, and Facey. In most fishes, these epurals make
little contribution to caudal fin support, and indeed, the original fin
membrane dorsal to the urostyle is resorbed as the fin ventral to the
urostyle develops rays, enlarges, and becomes both lobes of the caudal
fin supported by the hypurals. So, perhaps in your mudminnow fry, you
are seeing the remnants of the embryonic fin above the urostyle, not
yet resorbed, and the structure you see as a "spike" is probably the
urostyle extending directly posteriorly-in-this stage, rather than
angling up as is it does in most older fishes. The rays developing
ventral to the urostyle are the beginnings of both dorsal and ventral
lobes of the adult caudal fin.

Remember, I have not seen a juvenile mudminnow develop its caudal fin --
this is based on general developmental features of the caudal fin of
fishes.

Dave

David L. McNeely, Ph.D., Professor of Biology
Langston University; P.O. Box 1500
Langston, OK 73050; email: dlmcneely-in-lunet.edu
telephone: (405) 466-6025; fax: 405) 466-3307
home page http://www.lunet.edu/mcneely/index.htm

"Where are we going?" "I don't know, are we there yet?"

----- Original Message -----
From: Bob Muller <michiganfish-in-wideopenwest.com>
Date: Friday, May 13, 2005 3:26 pm
Subject: Re: NANFA-L-- mudminnow fry

> That was the first impression but mudminnows are not from the
> group that
> have the back bone going into the upper tail lobe. I put the fish
> under my
> microscope to look-in-the tail. On larva fish the dorsal, tail
> and anal fin
> start out as a fleshy membrane that wraps around the end of the
> fish and
> then divide and get fin rays. On the mudminnow the back bone is
> like a
> spike sticking beyond the tail fin. The lower tail fin is getting
> rays but
> the upper still looks like a membrane. Can any of the
> ichthyologists tell
> me what I am seeing.
> ----- Original Message -----
> From: <psalm119.111-in-juno.com>
> To: <nanfa-l-in-nanfa.org>
> Sent: Friday, May 13, 2005 12:53 PM
> Subject: RE: NANFA-L-- mudminnow fry
>
>
> >
> > Bob,
> > Is it like the tail fin of a young longnose gar?
> > Mike Lucas
> >
> > ___________________________________________________________________
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