Mean ± SE values of δ¹³C and δ¹⁵N, in muscle (M), blood (B) and fin (F) tissues of European catfish (top) and Northern pike (bottom) at four study sites (Most, Milada, Žlutice and Římov).

Significant differences between offset (means how given tissue is enriched or depleted compared to muscle tissue) of blood and muscle (B) and fin and muscle (F) (paired t-test) were examined. The C:N ratios were measured in three tissues of European catfish (top) and Northern pike (bottom). Asterisks indicate a significance (paired t-test, p > 0.05 = -, p < 0.05 = *, p < 0.01 = **, p < 0.001 = ***).