Dear Todd,
Sulphur isotope studies have been conducted on fish and other aquatic
animals for at least three decades. Some of the early work was done in
Russia by R.G.Pankina and V.L.Mekhtyeva. One paper by the latter reported on
the S-isotope composition of animal life in reservoirs of different
salinities ;Geokhimia 6,725-30;1971 (Russian).  I am not sure whether the
full paper was translated into English in GeoChem. Int 6, 461 or just the
abstract. There is a translated article by Mekhtyeva et al ,1976 entitled
"Distribution and isotopic compositions of forms of sulfur in water plants
and animals" , Geochem. Int. 13(5), 82-85.
I know that isotopes of sulfur and other elements have been used in at least
one study of fish migration. Salmon which spend their lives in both fresh
water and the ocean are interesting to study in this regard. I heard a
"rumor" of another study where a graduate student was trying to determine
the terrestrial input to a fish diet e.g. insects aliting on the water or
snapped in the air. Perhaps readers can cite some references.
Usually  H, C, N, O, and S  are all  isotopically heavier in marine animals
than in those in freshwater habitats . Exceptions arise in special
situations such as vent communities or where biogenic sulfide is somehow
incorporated into a food web.The trends in the fish reflect  the isotopic
compositions of water and  dissolved species.
Data which I have obtained and published are in a more general context  and
appear in chapters of books ( H.R.Krouse & V.A.Grinenko, Eds., 1991,  STABLE
ISOTOPES;  NATURAL AND ANTHROPOGENIC SULLPHUR IN THE ENVIRONMENT, 440pp,
SCOPE 43;   John Wiley & Sons) and technique-based papers (H.R.Krouse & A.
Ueda, 1987, Sulphur isotope analyses of trace sulphide and sulphate in
various materials using Kiba reagent, in STUDIES OF SULPHUR ISOTOPE
VARIATIONS IN NATURE,  113-121, IAEA, Vienna.).
Generally, fractionation during assimilation of sulfate tends to be small
(an exception being with yeast) with  delta 34S values of S in  organic
products being 2-5 per mil lower than that of  the sulfate. Higher animals
do not assimilate sulfate but can interconvert compounds such as S-amino
acids. S-isotope fractionation during such conversions seems to be very
small but very little has been published on specific reactions. The bottom
line in that  S-isotope shifts are established by bacterial and plant
assimilation  at lower levels in food webs and the shifts in going to
successively higher trophic levels are small.
We have found trace sulfate in fish teeth to be interesting isotopically.
Its delta 34S value is consistant with the oxidation of organic-S and
therefore tends to be a few per mil lower than sulphate in the water.
I hope this brief response answers your questions.
With tongue in cheek, I ask if anyone has considered studying terrestrial
contributions to the diets of Piranha?
In terms of quantities required for analyses, it depends upon whether you
have continuous flow mass spectrometric facilities which can give data with
a few micrograms of sulfur or traditional facilities where about 5 mg S is
desirable. Also the sulfur content of fish varies. It is  dependent upon
concentration of sulfate in water but the relationship is not a proportional
one because individual important bio-organic S-compounds have fixed S/C
ratios.
Roy Krouse



From: "Todd Miller" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Monday, February 24, 2003 9:40 AM
Subject: 34S of marine organisms


> Greetings,
>
> I have several questions regarding use of sulfur stable isotopes,
> particularly in the marine environment.  Understandably, 34S has been used
> on microbial systems (marshes, estuarine and hydrothermal vent
> communities), with the general trend being marine sulfur to be more
> enriched than freshwater/estuarine.  My question is, why has sulfur not
> been applied to marine zooplankton and fish?  To my knowledge, very little
> work has been done on this.  My guess is that once in the marine
> environment, sulfur values vary and are not linked to any particular
> (known) mechanism/process.  Another question is, how much material do I
> need for sulfur analysis of marine zooplankton and fish.
>
> If anyone out there has ideas or thoughts on this (or references!), it
> would be greatly appreciated!
>
> Sincerely,
> Todd