Turnover rates and trophic discrimination factors of δ34s in brook trout, Salvelinus fontinalis

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University of New Brunswick


Stable isotope analysis (SIA) of sulphur, like carbon and nitrogen SIA, can be applied to understand food webs, animal movements, and nutrient dynamics. Sulphur SIA is of particular interest for movement studies of anadromous fishes because of the large variation between freshwater and marine sulphur (δ34S) stable isotope values. The application of this tool is dependent on our knowledge of the isotopic change between a consumer and its diet or the trophic discrimination factor (Δδ34S), and the turnover rate of the element in the organism’s tissues. The objectives of this study were to determine the Δδ34S and turnover rate of sulphur in liver, muscle, blood and caudal fin tissues, of brook trout (Salvelinus fontinalis), using laboratory and field experiments. At the start of the laboratory experiment, brook trout were fed a diet with a δ34S value of 5.8±0.3‰, relative to their previous diet that had a δ34S value of 15.9±0.2‰. For the field experiment, hatchery-reared brook trout were introduced to a New Brunswick stream, where their sulphur turnover rate and Δδ34S were monitored in situ. These trout had an initial δ34S value that was high relative to their natural diet in the stream. Subsequent sampling over several months permitted a comparison of natural and laboratory-derived turnover rates of sulphur in their tissues. The turnover rates from the laboratory results indicated the sulphur turnover was most rapid in liver and caudal fin and was slowest in blood and muscle. Similar turnover results were found in the field experiment. Laboratory measured Δδ34S of those tissues that reached steady state averaged ~1‰ and the average Δδ34S for all the tissues sampled from the Otter Brook resident brook trout in the field experiment was ~ 0 ‰. Results of this study will facilitate the use of sulphur as a third isotopic tracer in food web studies, and to successfully track fish movements.