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Subject: Summary: Otolith Marking Longevity (OTC-vs-Strontium)
From: Paul Brown <[log in to unmask]>
Reply-To:Academic forum on fisheries ecology and related topics <[log in to unmask]>
Date:Fri, 20 Dec 1996 10:56:43 +1100

text/plain (130 lines)

My original posting was as follows:

> There seems to be a wealth of literature concearning the use of chemicals
> such as OTC, alizarin, calcein etc for marking fish otoliths. Most of this
> is published after the techniques are developed for a new species or a new
> chemical and explore the mark-success rate, and associated mortality rate.
> Some even consider detection-rates after a short period of time. However,
> what's lacking is the long-term story. Do these substances provide good,
> long-term marks in otoliths?
> We have an application, in which we wish to batch-mark Australian freshwater
> fish fingerlings 25-50 mm(by immersion) so that we can discriminate between
> wild-recruited, and stocked fish at a later date (i.e. 12 months to a few
> years later).
> Has anyone out there got any case-histories / recommendations /
> horror-stories to tell about the longevity of fluorochrome marks ??

I thank all the respondants for much useful information and look forward to
some further dialogue on this matter. A summary of responses took in both
fluorochrome and strontium marking experiences as follows:

Bruno Schneider([log in to unmask]) Wrote of experience in Switzerland
on brown trout marked with Tetracyclin:

"In the laboratory experiment the visibility of the marks was still good and
no signs of
fading or something like this could be detected...
After my opinion, tetracyclin-mark retention is good enough for studies
with a duration of one year and longer. One major problem I am struggling
with is to control the effects of the marking method. My experiences with
the same marking procedure range from 100 % mortality over no mortality, but
poor marking to no mortality with very good mark quality."

Dave Secor <[log in to unmask]> talked about immersion mass marking of
hatchery-produced larval and juvenile striped bass with oxytetracycline and
described "..retention for a seven
month period.  Since that time we have observed marks in fish up to 4
years in age in the Santee-Cooper system.  The problem is probably not
retention but detection in older fishes due to difficulty in locating
small diameter marks in larger otoliths."

Audrey Geffen, ([log in to unmask]) described two "long-term" validation
studies :

1) Fargo, J. & Chilton, D.E. 1987. Age validation for rock sole in Hecate Strait
British Columbia. Trans Am Fish Soc. 115:34-40

They injected with OTC and recaptured 2-3 years later

2) Leaman, B.M. & Nagtegaal, D.A. 1987. Age validation and revised natural
mortality rate for yellowtail rockfish. Trans. Am. Fish. Soc. 116:171-175.

They also injected with OTC and recaptured up to 4 years later.

Tom Reinert <[log in to unmask]> wrote about a recently
submitted manuscript where OTC marked striped bass were double marked with
coded wire tags.  "Recoveries up to 3 yrs post
stocking has allowed us to evaluate the effectiveness of OTC (we had
already examined retention of CWT).  Retention and detection are
intimately twined. If you do not find an OTC mark, was it not
retained or simply not detected?  With double tagged fish, we were
able to separate the two. In our study, we found ~74% detection with
no correlation to fish age (and hence, otolith size).  All otoliths
required sectioning and polishing.  Detection would undoubtedly be
higher if otoliths were small enough to require no preparation at
all.  Retention was approximately 80%.  All mark loss occurred with
in the first year, according to our models.

Ron Brooks <[log in to unmask]> described the examination of OTC marks in
several  USA,freshwater species...

"Thus, based on what we have seen, it appears that OTC marks should last
at least 5 years in otoliths of freshwater fish with which we have
worked. Illinois is currently involved with several stocking assesment
projects that use OTC as a marking agent."

Curtis Knudsen <[log in to unmask]> brought the discussion around to
strontium marking and described the results of their work on Sr-immersion
marked salmonids.

"This technique has been successfully applied to sockeye salmon, coho
salmon, chinook salmon, Atlantic salmon, brown trout, and chum salmon.
The mark has persisted for at least 21 months and has not produced any
negative side effects."

Curtis went further to say..."In regards to cheap detection:
we've notice in salmonids that the strontium mark is visible using
standard light microscopy.  If you have the fish in your "hands" for a
number of days, preferably a few weeks, you could put down a series of
marks (wide and narrowly spaced) separated by 2 or 4 days between events.
There need to be enough of these visible bands so that it is clear that an
artificial pattern exists on the otolith.  That is, distinguish marked
fish from fish with natural levels of background "noise" banding patterns
due to daily bands, thermal events, stress events, etc.  A consistant
pattern of wide and narrow bands is the key.  We have put down  distinct
multiple strontium bands by immersing fish for <12 hr in <1,000 ppm
SrCl solutions separated by 7 day periods."

Also on strontium marking.. Eric Volk <[log in to unmask]> added.. " I usually
find marks to be so clear that quantitative analysis is unnecessary, and
simple back-scattered electron images are sufficient to detect
differences between disparate treatments.

******************* IN CONCLUSION ********************************
So it seems to me that although fluorochromes such as OTC (the only type
used by respondants) seem to be the more proven long-term markers, strontium
still has a place and in fact may be visualised by light-microscopy or at
least by SEM back-scattered imagery. As far as our work goes we may have to
pursue both methods and do an evaluation.

thanks again to all respondants.
Paul Brown
Senior Scientist, Inland Systems Division
Marine and Freshwater Resources Institute
Snobs Creek
Private Bag 20
VIC 3714

ph: 03 57 742208
fax: 03 57 742659
email: [log in to unmask]

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