(1) The crucian carp were captured using baited traps from natural populations in two adjacent ponds in Southern England. The carp were sourced from a local hatchery.
(2) Juveniles of both species were sourced from local hatcheries and released into three adjacent (but unconnected), fishless former aquaculture ponds. The samples of fish fin and macroinvertebrates were taken for extracting stable isotope values.
(3) Four wild ponds located in southern England where fish were sampled by a combination of baited fish traps and rod and line angling during stock assessment exercises, where the species were identified, measured (FL, nearest mm) and scale samples taken (3 to 5 scales per fish) for extracting stable isotope values.