Growth and morphology of an endangered native freshwater fish,crucian carp Carassius carassius,in an English ornamental pond

• 1. Crucian carp Carassius carassius, which is native to south‐east England, has received little previous study in Britain but is threatened by introductions of goldfish Carassius auratus through hybridization and by frequent mis‐identification of brown goldfish as crucian carp. The present study provides the first data on back‐calculated growth, morphology and age‐at‐maturity of crucian carp in Britain.
• 2. The youngest mature crucian were female (age 2+), the smallest mature crucian were male (age 3+), with almost all fish mature at age 3+. Sex dimorphism in back‐calculated standard length at age was not observed except at age 2+ (juveniles longest). Shifts in morphological characters often associated with maturation (dorsal and ventral fin length, dorsal and anal fin depth, pre‐dorsal distance, body width) were observed between ages 4+ and 7+, which (in contrast to the relatively abrupt shift in maturity) suggests that age and size at maturation may not reflect the size and age of active (i.e. real) spawning.
• 3. Back‐calculated standard lengths at age for crucian carp were intermediate relative to other European populations, indicating that environmental conditions in England appear to be well suited to the species despite being at the westernmost extent of the species' native European range. The management of ornamental ponds specifically for crucian carp is discussed.

© Crown copyright 2007. Reproduced with the permission of Her Majesty's Stationery Office. Published by John Wiley & Sons, Ltd.