| Summary: | For many applications and ecological studies in which wild individuals are brought to
laboratory it would be essential to know accurately how fast novel diet is reflected in
composition of different tissues. To study the effects of two different diets on the
stable isotope composition of freshwater crayfish muscle and hemolymph, we conducted a
three month experiment on noble crayfish (Astacus astacus) and signal
crayfish (Pacifastacus leniusculus) by feeding them sweet corn
(Zea mays) or Baltic herring (Clupea harengus membras)
as novel food. During the experiment, the crayfish were given 0.4 g of selected food daily
and the amount consumed was recorded. The samples for the stable isotope analyses were
taken at the commencement of the experiment (initial control) and three times (hemolymph)
or twice (muscle tissue) during the experiment. We found that stable isotope changes can
be similarly, and rather slowly, detected from muscle tissue and hemolymph under studied
conditions. Hemolymph sampling, being non-lethal, can be recommended as a practical
sampling method. Our results confirm earlier reports according to which diet changes
reflect to crayfish isotope ratios slowly implying that isotope ratios indicate long-term
diet.
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